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<TITLE>Evolution of the eye - Wikipedia</TITLE>

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<H1 id="firstHeading" class="firstHeading" lang="en">Evolution of the eye</H1>			<DIV id="bodyContent" class="mw-body-content">
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<DIV class="thumbinner" style="width:352px;"><A href="/wiki/File:Diagram_of_eye_evolution.svg" class="image"><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Diagram_of_eye_evolution.svg/350px-Diagram_of_eye_evolution.svg.png" width="350" height="488" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Diagram_of_eye_evolution.svg/525px-Diagram_of_eye_evolution.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/b/b6/Diagram_of_eye_evolution.svg/700px-Diagram_of_eye_evolution.svg.png 2x" data-file-width="584" data-file-height="815" /></A>
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Major stages in the evolution of the eye in <A href="/wiki/Vertebrates" class="mw-redirect" title="Vertebrates">vertebrates</A>.</DIV>
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<P>The <B>evolution of the eye</B> is attractive to study, because the <A href="/wiki/Eye" title="Eye">eye</A> distinctively exemplifies an <A href="/wiki/Convergent_evolution" title="Convergent evolution">analogous</A> <A href="/wiki/Organ_(anatomy)" title="Organ (anatomy)">organ</A> found in many <A href="/wiki/Taxon" title="Taxon">animal forms</A>. Complex, image-forming eyes have evolved independently several times.<SUP id="cite_ref-1" class="reference"><A href="#cite_note-1">[1]</A></SUP> The evolutionary geneticist Walter Gering holds a different opinion. According his theory, the genes engaged with photoreceptor cells (so called Pax 6 genes) appeared probably at once in the life history, at a very early stage of the evolution. <SUP id="cite_ref-2" class="reference"><A href="#cite_note-2">[2]</A></SUP> Probably, the complex, image forming kinds of eyes are at least five: Chidaria - lens eye, complex eye; Molluscs - lens eye, everse retina; Annelids- lens eye, everse retina; Arthropods - facet eye; Vertebrate- lens eye, inverse retina <SUP id="cite_ref-3" class="reference"><A href="#cite_note-3">[3]</A></SUP></P>
<P>Complex eyes appeared first within the few million years of the <A href="/wiki/Cambrian_explosion" title="Cambrian explosion">Cambrian explosion</A>. From before the <A href="/wiki/Cambrian" title="Cambrian">Cambrian</A>, no evidence of eyes has survived, but diverse eyes are known from the <A href="/wiki/Burgess_shale" class="mw-redirect" title="Burgess shale">Burgess shale</A> of the Middle Cambrian, and from the slightly older <A href="/wiki/Emu_Bay_Shale" title="Emu Bay Shale">Emu Bay Shale</A>.<SUP id="cite_ref-4" class="reference"><A href="#cite_note-4">[4]</A></SUP> Eyes are adapted to the various requirements of their owners. They vary in their <A href="/wiki/Visual_acuity" title="Visual acuity">visual acuity</A>, the range of wavelengths they can detect, their sensitivity in low light, their ability to detect motion or to resolve objects, and whether they can <A href="/wiki/Colour_vision" class="mw-redirect" title="Colour vision">discriminate colours</A>.</P>
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<H2>Contents</H2>
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<LI class="toclevel-1 tocsection-1"><A href="#History_of_research"><SPAN class="tocnumber">1</SPAN> <SPAN class="toctext">History of research</SPAN></A></LI>
<LI class="toclevel-1 tocsection-2"><A href="#Rate_of_evolution"><SPAN class="tocnumber">2</SPAN> <SPAN class="toctext">Rate of evolution</SPAN></A></LI>
<LI class="toclevel-1 tocsection-3"><A href="#One_origin_or_many?"><SPAN class="tocnumber">3</SPAN> <SPAN class="toctext">One origin or many?</SPAN></A></LI>
<LI class="toclevel-1 tocsection-4"><A href="#Stages_of_eye_evolution"><SPAN class="tocnumber">4</SPAN> <SPAN class="toctext">Stages of eye evolution</SPAN></A>
<UL>
<LI class="toclevel-2 tocsection-5"><A href="#Early_eyes"><SPAN class="tocnumber">4.1</SPAN> <SPAN class="toctext">Early eyes</SPAN></A></LI>
<LI class="toclevel-2 tocsection-6"><A href="#Lens_formation_and_diversification"><SPAN class="tocnumber">4.2</SPAN> <SPAN class="toctext">Lens formation and diversification</SPAN></A></LI>
<LI class="toclevel-2 tocsection-7"><A href="#Other_developments"><SPAN class="tocnumber">4.3</SPAN> <SPAN class="toctext">Other developments</SPAN></A>
<UL>
<LI class="toclevel-3 tocsection-8"><A href="#Color_vision"><SPAN class="tocnumber">4.3.1</SPAN> <SPAN class="toctext">Color vision</SPAN></A></LI>
<LI class="toclevel-3 tocsection-9"><A href="#Polarization_vision"><SPAN class="tocnumber">4.3.2</SPAN> <SPAN class="toctext">Polarization vision</SPAN></A></LI>
<LI class="toclevel-3 tocsection-10"><A href="#Focusing_mechanism"><SPAN class="tocnumber">4.3.3</SPAN> <SPAN class="toctext">Focusing mechanism</SPAN></A></LI>
<LI class="toclevel-3 tocsection-11"><A href="#Location"><SPAN class="tocnumber">4.3.4</SPAN> <SPAN class="toctext">Location</SPAN></A></LI>
</UL>
</LI>
</UL>
</LI>
<LI class="toclevel-1 tocsection-12"><A href="#Evolutionary_baggage"><SPAN class="tocnumber">5</SPAN> <SPAN class="toctext">Evolutionary baggage</SPAN></A></LI>
<LI class="toclevel-1 tocsection-13"><A href="#Footnotes"><SPAN class="tocnumber">6</SPAN> <SPAN class="toctext">Footnotes</SPAN></A></LI>
<LI class="toclevel-1 tocsection-14"><A href="#See_also"><SPAN class="tocnumber">7</SPAN> <SPAN class="toctext">See also</SPAN></A></LI>
<LI class="toclevel-1 tocsection-15"><A href="#References"><SPAN class="tocnumber">8</SPAN> <SPAN class="toctext">References</SPAN></A></LI>
<LI class="toclevel-1 tocsection-16"><A href="#Further_reading"><SPAN class="tocnumber">9</SPAN> <SPAN class="toctext">Further reading</SPAN></A></LI>
<LI class="toclevel-1 tocsection-17"><A href="#External_links"><SPAN class="tocnumber">10</SPAN> <SPAN class="toctext">External links</SPAN></A></LI>
</UL>
</DIV>
<P></P>
<H2><SPAN class="mw-headline" id="History_of_research">History of research</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=1" title="Edit section: History of research">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
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<DIV class="thumbinner" style="width:267px;"><A href="/wiki/File:Eye_iris.jpg" class="image"><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Eye_iris.jpg/265px-Eye_iris.jpg" width="265" height="177" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Eye_iris.jpg/398px-Eye_iris.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/65/Eye_iris.jpg/530px-Eye_iris.jpg 2x" data-file-width="2788" data-file-height="1864" /></A>
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The human eye, showing the <A href="/wiki/Iris_(anatomy)" title="Iris (anatomy)">iris</A></DIV>
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<P>In 1802, philosopher <A href="/wiki/William_Paley" title="William Paley">William Paley</A> called it a miracle of "<A href="/wiki/Design" title="Design">design</A>". <A href="/wiki/Charles_Darwin" title="Charles Darwin">Charles Darwin</A> himself wrote in his <I><A href="/wiki/Origin_of_Species" class="mw-redirect" title="Origin of Species">Origin of Species</A></I>, that the evolution of the eye by natural selection seemed at first glance "absurd in the highest possible degree". However, he went on that despite the difficulty in imagining it, its evolution was perfectly feasible:</P>
<BLOCKQUOTE>
<P>...if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered as subversive of the theory.<SUP id="cite_ref-origin_5-0" class="reference"><A href="#cite_note-origin-5">[5]</A></SUP></P>
</BLOCKQUOTE>
<P>He suggested a stepwise evolution from "an optic nerve merely coated with pigment, and without any other mechanism" to "a moderately high stage of perfection", and gave examples of existing intermediate steps.<SUP id="cite_ref-origin_5-1" class="reference"><A href="#cite_note-origin-5">[5]</A></SUP> Darwin's suggestions were soon shown to be correct, and current research is investigating the genetic mechanisms underlying eye development and evolution.<SUP id="cite_ref-6" class="reference"><A href="#cite_note-6">[6]</A></SUP></P>
<P>Biologist <A href="/w/index.php?title=D.E._Nilsson&action=edit&redlink=1" class="new" title="D.E. Nilsson (page does not exist)">D.E. Nilsson</A> has independently theorized about four general stages in the evolution of a vertebrate eye from a patch of photoreceptors.<SUP id="cite_ref-7" class="reference"><A href="#cite_note-7">[7]</A></SUP> Nilsson and S. Pelger estimated in a classical paper how many generations are needed to evolve a complex eye in vertebrates.<SUP id="cite_ref-Nilsson,_D_1994_8-0" class="reference"><A href="#cite_note-Nilsson,_D_1994-8">[8]</A></SUP> Another researcher, G.C. Young, has used the fossil record to infer evolutionary conclusions, based on the structure of eye orbits and openings in fossilized skulls for blood vessels and nerves to go through.<SUP id="cite_ref-9" class="reference"><A href="#cite_note-9">[9]</A></SUP> All this adds to the growing amount of evidence that supports Darwin's theory.</P>
<H2><SPAN class="mw-headline" id="Rate_of_evolution">Rate of evolution</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=2" title="Edit section: Rate of evolution">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<P>The first fossils of eyes found to date are from the lower <A href="/wiki/Cambrian" title="Cambrian">Cambrian</A> period (about <SPAN class="nourlexpansion plainlinks" style="white-space:nowrap;"><A class="external text" href="http://tools.wmflabs.org/timescale/?Ma=540">540</A> million years ago</SPAN>).<SUP id="cite_ref-Parker2009_10-0" class="reference"><A href="#cite_note-Parker2009-10">[10]</A></SUP> The lower Cambrian had a burst of apparently rapid evolution, called the "<A href="/wiki/Cambrian_explosion" title="Cambrian explosion">Cambrian explosion</A>". One of the many hypotheses for "causes" of the Cambrian explosion is the "Light Switch" theory of <A href="/wiki/Andrew_Parker_(zoologist)" title="Andrew Parker (zoologist)">Andrew Parker</A>: It holds that the evolution of eyes started an <A href="/wiki/Red_queen_hypothesis" class="mw-redirect" title="Red queen hypothesis">arms race</A> that accelerated evolution.<SUP id="cite_ref-parker2003_11-0" class="reference"><A href="#cite_note-parker2003-11">[11]</A></SUP> Before the Cambrian explosion, animals may have sensed light, but did not use it for fast locomotion or navigation by vision.</P>
<P>The rate of eye evolution is difficult to estimate, because the fossil record, particularly of the lower Cambrian, is poor. How fast a circular patch of photoreceptor cells evolve into a fully functional vertebrate eye has been estimated based on rates of mutation, relative advantage to the organism, and natural selection. However, the time needed for each state was consistently overestimated and the generation time was set to one year, which is common in small animals. Even with these pessimistic values, the vertebrate eye would still evolve from a patch of photoreceptor cells in less than 364,000 years.<SUP id="cite_ref-Nilsson1994_12-0" class="reference"><A href="#cite_note-Nilsson1994-12">[12]</A></SUP><SUP id="cite_ref-13" class="reference"><A href="#cite_note-13">[note 1]</A></SUP></P>
<H2><SPAN id="One_origin_or_many.3F"></SPAN><SPAN class="mw-headline" id="One_origin_or_many?">One origin or many?</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=3" title="Edit section: One origin or many?">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<P>Whether the eye evolved once or many times depends on the definition of an eye. All eyed animals share much of the genetic machinery for eye development. This suggests that the ancestor of eyed animals had some form of light-sensitive machinery – even if it was not a dedicated optical organ. However, even photoreceptor cells may have evolved more than once from molecularly similar chemoreceptor cells. Probably, photoreceptor cells existed long before the Cambrian explosion.<SUP id="cite_ref-Nilsson1996_14-0" class="reference"><A href="#cite_note-Nilsson1996-14">[13]</A></SUP> Higher-level similarities – such as the use of the protein <A href="/wiki/Crystallin" title="Crystallin">crystallin</A> in the independently derived cephalopod and vertebrate lenses<SUP id="cite_ref-15" class="reference"><A href="#cite_note-15">[14]</A></SUP> – reflect the <A href="/wiki/Exaptation" title="Exaptation">co-option</A> of a more fundamental protein to a new function within the eye.<SUP id="cite_ref-Scotland2010_16-0" class="reference"><A href="#cite_note-Scotland2010-16">[15]</A></SUP></P>
<P>A shared trait common to all light-sensitive organs are <A href="/wiki/Opsin" title="Opsin">opsins</A>. Opsins belong to a family of photo-sensitive proteins and fall into nine groups, which already existed in the <A href="/wiki/Urbilaterian" title="Urbilaterian">urbilaterian</A>, the last common ancestor of all <A href="/wiki/Bilateria" title="Bilateria">bilateral symmetrical animals</A>.<SUP id="cite_ref-17" class="reference"><A href="#cite_note-17">[16]</A></SUP> Additionally, the genetic toolkit for positioning eyes is shared by all animals: The <A href="/wiki/PAX6" title="PAX6">PAX6 gene</A> controls where eyes develop in animals ranging from octopuses<SUP id="cite_ref-18" class="reference"><A href="#cite_note-18">[17]</A></SUP> to mice and <A href="/wiki/Drosophila_melanogaster" title="Drosophila melanogaster">fruit flies</A>.<SUP id="cite_ref-19" class="reference"><A href="#cite_note-19">[18]</A></SUP><SUP id="cite_ref-20" class="reference"><A href="#cite_note-20">[19]</A></SUP><SUP id="cite_ref-21" class="reference"><A href="#cite_note-21">[20]</A></SUP> Such high-level genes are, by implication, much older than many of the structures that they control today; they must originally have served a different purpose, before they were co-opted for eye development.<SUP id="cite_ref-Scotland2010_16-1" class="reference"><A href="#cite_note-Scotland2010-16">[15]</A></SUP></P>
<P>Eyes and other sensory organs probably evolved before the brain: There is no need for an information-processing organ (brain) before there is information to process.<SUP id="cite_ref-Gehring_22-0" class="reference"><A href="#cite_note-Gehring-22">[21]</A></SUP></P>
<H2><SPAN class="mw-headline" id="Stages_of_eye_evolution">Stages of eye evolution</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=4" title="Edit section: Stages of eye evolution">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
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<DIV class="thumbinner" style="width:132px;"><A href="/wiki/File:Augentierchen_440x600.jpg" class="image"><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/1/17/Augentierchen_440x600.jpg/130px-Augentierchen_440x600.jpg" width="130" height="177" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/17/Augentierchen_440x600.jpg/195px-Augentierchen_440x600.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/17/Augentierchen_440x600.jpg/260px-Augentierchen_440x600.jpg 2x" data-file-width="440" data-file-height="599" /></A>
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The <I>stigma</I> (2) of the <A href="/wiki/Euglena" title="Euglena">euglena</A> hides a light-sensitive spot.</DIV>
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<P>The earliest predecessors of the eye were photoreceptor proteins that sense light, found even in unicellular organisms, called "<A href="/wiki/Eyespot_apparatus" title="Eyespot apparatus">eyespots</A>". Eyespots can only sense ambient brightness: they can distinguish light from dark, sufficient for <A href="/wiki/Photoperiodism" title="Photoperiodism">photoperiodism</A> and daily synchronization of <A href="/wiki/Circadian_rhythm" title="Circadian rhythm">circadian rhythms</A>. They are insufficient for vision, as they cannot distinguish shapes or determine the direction light is coming from. Eyespots are found in nearly all major animal groups, and are common among unicellular organisms, including <A href="/wiki/Euglena" title="Euglena">euglena</A>. The euglena's eyespot, called a <I>stigma</I>, is located at its anterior end. It is a small splotch of red pigment which shades a collection of light sensitive crystals. Together with the leading flagellum, the eyespot allows the organism to move in response to light, often toward the light to assist in <A href="/wiki/Photosynthesis" title="Photosynthesis">photosynthesis</A>,<SUP id="cite_ref-Land1992_23-0" class="reference"><A href="#cite_note-Land1992-23">[22]</A></SUP> and to predict day and night, the primary function of circadian rhythms. Visual pigments are located in the brains of more complex organisms, and are thought to have a role in synchronising spawning with lunar cycles. By detecting the subtle changes in night-time illumination, organisms could synchronise the release of sperm and eggs to maximise the probability of fertilisation.<SUP class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<I><A href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><SPAN title="This claim needs references to reliable sources. (May 2011)">citation needed</SPAN></A></I>]</SUP></P>
<P>Vision itself relies on a basic biochemistry which is common to all eyes. However, how this biochemical toolkit is used to interpret an organism's environment varies widely: eyes have a wide range of structures and forms, all of which have evolved quite late relative to the underlying proteins and molecules.<SUP id="cite_ref-Land1992_23-1" class="reference"><A href="#cite_note-Land1992-23">[22]</A></SUP></P>
<P>At a cellular level, there appear to be two main "designs" of eyes, one possessed by the <A href="/wiki/Protostomes" class="mw-redirect" title="Protostomes">protostomes</A> (<A href="/wiki/Mollusc" class="mw-redirect" title="Mollusc">molluscs</A>, <A href="/wiki/Annelids" class="mw-redirect" title="Annelids">annelid worms</A> and <A href="/wiki/Arthropod" title="Arthropod">arthropods</A>), the other by the <A href="/wiki/Deuterostomes" class="mw-redirect" title="Deuterostomes">deuterostomes</A> (<A href="/wiki/Chordate" title="Chordate">chordates</A> and <A href="/wiki/Echinoderm" title="Echinoderm">echinoderms</A>).<SUP id="cite_ref-Land1992_23-2" class="reference"><A href="#cite_note-Land1992-23">[22]</A></SUP></P>
<P>The functional unit of the eye is the photoreceptor cell, which contains the opsin proteins and responds to light by initiating a nerve impulse. The light sensitive opsins are borne on a hairy layer, to maximise the surface area. The nature of these "hairs" differs, with two basic forms underlying photoreceptor structure: <A href="/wiki/Microvillus" title="Microvillus">microvilli</A> and <A href="/wiki/Cilium" title="Cilium">cilia</A>.<SUP id="cite_ref-Autrum1979_24-0" class="reference"><A href="#cite_note-Autrum1979-24">[23]</A></SUP> In the eyes of protostomes, they are microvilli: extensions or protrusions of the cellular membrane. But in the eyes of deuterostomes, they are derived from cilia, which are separate structures.<SUP id="cite_ref-Land1992_23-3" class="reference"><A href="#cite_note-Land1992-23">[22]</A></SUP> However, outside the eyes an organism may use the other type of photoreceptor cells, for instance the clamworm <A href="/wiki/Platynereis_dumerilii" title="Platynereis dumerilii">Platynereis dumerilii</A> uses microvilliar cells in the eyes but has additionally deep brain ciliary photoreceptor cells.<SUP id="cite_ref-Arendt2004_25-0" class="reference"><A href="#cite_note-Arendt2004-25">[24]</A></SUP> The actual derivation may be more complicated, as some microvilli contain traces of cilia — but other observations appear to support a fundamental difference between protostomes and deuterostomes.<SUP id="cite_ref-Land1992_23-4" class="reference"><A href="#cite_note-Land1992-23">[22]</A></SUP> These considerations centre on the response of the cells to light – some use sodium to cause the electric signal that will form a nerve impulse, and others use potassium; further, protostomes on the whole construct a signal by allowing <I>more</I> sodium to pass through their cell walls, whereas deuterostomes allow less through.<SUP id="cite_ref-Land1992_23-5" class="reference"><A href="#cite_note-Land1992-23">[22]</A></SUP></P>
<P>This suggests that when the two lineages diverged in the Precambrian, they had only very primitive light receptors, which developed into more complex eyes independently.</P>
<H3><SPAN class="mw-headline" id="Early_eyes">Early eyes</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=5" title="Edit section: Early eyes">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<P>The basic light-processing unit of eyes is the <A href="/wiki/Photoreceptor_cell" title="Photoreceptor cell">photoreceptor cell</A>, a specialized cell containing two types of molecules in a membrane: the <A href="/wiki/Opsin" title="Opsin">opsin</A>, a light-sensitive protein, surrounding the <A href="/wiki/Chromophore" title="Chromophore">chromophore</A>, a <A href="/wiki/Pigment" title="Pigment">pigment</A> that distinguishes colors. Groups of such cells are termed "eyespots", and have evolved independently somewhere between 40 and 65 times. These eyespots permit animals to gain only a very basic sense of the direction and intensity of light, but not enough to discriminate an object from its surroundings.<SUP id="cite_ref-Land1992_23-6" class="reference"><A href="#cite_note-Land1992-23">[22]</A></SUP></P>
<P>Developing an optical system that can discriminate the direction of light to within a few degrees is apparently much more difficult, and only six of the thirty-some phyla<SUP id="cite_ref-26" class="reference"><A href="#cite_note-26">[note 2]</A></SUP> possess such a system. However, these phyla account for 96% of living species.<SUP id="cite_ref-Land1992_23-7" class="reference"><A href="#cite_note-Land1992-23">[22]</A></SUP></P>
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The <A href="/wiki/Planarian" title="Planarian">planarian</A> has "cup" eyespots that can slightly distinguish light direction.</DIV>
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<P>These complex optical systems started out as the multicellular eyepatch gradually depressed into a cup, which first granted the ability to discriminate brightness in directions, then in finer and finer directions as the pit deepened. While flat eyepatches were ineffective at determining the direction of light, as a beam of light would activate exactly the same patch of photo-sensitive cells regardless of its direction, the "cup" shape of the pit eyes allowed limited directional differentiation by changing which cells the lights would hit depending upon the light's angle. Pit eyes, which had arisen by the <A href="/wiki/Cambrian" title="Cambrian">Cambrian</A> period, were seen in ancient <A href="/wiki/Snail" title="Snail">snails</A>,<SUP class="noprint Inline-Template" style="margin-left:0.1em; white-space:nowrap;">[<I><A href="/wiki/Wikipedia:Please_clarify" title="Wikipedia:Please clarify"><SPAN title="The text near this tag may need clarification or removal of jargon. (December 2008)">clarification needed</SPAN></A></I>]</SUP> and are found in some snails and other invertebrates living today, such as <A href="/wiki/Planaria" title="Planaria">planaria</A>. Planaria can slightly differentiate the direction and intensity of light because of their cup-shaped, heavily pigmented <A href="/wiki/Retina" title="Retina">retina</A> cells, which shield the light-sensitive cells from exposure in all directions except for the single opening for the light. However, this proto-eye is still much more useful for detecting the absence or presence of light than its direction; this gradually changes as the eye's pit deepens and the number of photoreceptive cells grows, allowing for increasingly precise visual information.<SUP id="cite_ref-ee_27-0" class="reference"><A href="#cite_note-ee-27">[25]</A></SUP></P>
<P>When a <A href="/wiki/Photon" title="Photon">photon</A> is absorbed by the chromophore, a chemical reaction causes the photon's energy to be transduced into electrical energy and relayed, in higher animals, to the <A href="/wiki/Nervous_system" title="Nervous system">nervous system</A>. These photoreceptor cells form part of the <A href="/wiki/Retina" title="Retina">retina</A>, a thin layer of cells that relays <A href="/wiki/Visual_perception" title="Visual perception">visual</A> information,<SUP id="cite_ref-photons_28-0" class="reference"><A href="#cite_note-photons-28">[26]</A></SUP> including the light and day-length information needed by the circadian rhythm system, to the brain. However, some <A href="/wiki/Jellyfish" title="Jellyfish">jellyfish</A>, such as Cladonema, have elaborate eyes but no brain. Their eyes transmit a message directly to the muscles without the intermediate processing provided by a brain.<SUP id="cite_ref-Gehring_22-1" class="reference"><A href="#cite_note-Gehring-22">[21]</A></SUP></P>
<P>During the <A href="/wiki/Cambrian_explosion" title="Cambrian explosion">Cambrian explosion</A>, the development of the eye accelerated rapidly, with radical improvements in image-processing and detection of light direction.<SUP id="cite_ref-29" class="reference"><A href="#cite_note-29">[27]</A></SUP></P>
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<DIV class="thumbinner" style="width:202px;"><A href="/wiki/File:Nautilus_pompilius_(head).jpg" class="image"><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Nautilus_pompilius_%28head%29.jpg/200px-Nautilus_pompilius_%28head%29.jpg" width="200" height="133" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Nautilus_pompilius_%28head%29.jpg/300px-Nautilus_pompilius_%28head%29.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/9c/Nautilus_pompilius_%28head%29.jpg/400px-Nautilus_pompilius_%28head%29.jpg 2x" data-file-width="4272" data-file-height="2848" /></A>
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The primitive <A href="/wiki/Nautilus" title="Nautilus">nautilus</A> eye functions similarly to a <A href="/wiki/Pinhole_camera" title="Pinhole camera">pinhole camera</A>.</DIV>
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<P>After the photosensitive cell region invaginated, there came a point when reducing the width of the light opening became more efficient at increasing visual resolution than continued deepening of the cup.<SUP id="cite_ref-Nilsson1994_12-1" class="reference"><A href="#cite_note-Nilsson1994-12">[12]</A></SUP> By reducing the size of the opening, organisms achieved true imaging, allowing for fine directional sensing and even some shape-sensing. Eyes of this nature are currently found in the <A href="/wiki/Nautilus" title="Nautilus">nautilus</A>. Lacking a cornea or lens, they provide poor resolution and dim imaging, but are still, for the purpose of vision, a major improvement over the early eyepatches.<SUP id="cite_ref-dawkins_30-0" class="reference"><A href="#cite_note-dawkins-30">[28]</A></SUP></P>
<P>Overgrowths of transparent cells prevented contamination and parasitic infestation. The chamber contents, now segregated, could slowly specialize into a transparent humour, for optimizations such as colour filtering, higher <A href="/wiki/Refractive_index" title="Refractive index">refractive index</A>, blocking of <A href="/wiki/Ultraviolet" title="Ultraviolet">ultraviolet</A> radiation, or the ability to operate in and out of water. The layer may, in certain classes, be related to the <A href="/wiki/Ecdysis" title="Ecdysis">moulting</A> of the organism's shell or skin. An example of this can be observed in <A href="/wiki/Onychophorans" class="mw-redirect" title="Onychophorans">Onychophorans</A> where the cuticula of the shell continues to the cornea. The cornea is composed of either one or two cuticular layers depending on how recently the animal has moulted.<SUP id="cite_ref-Schoenemann2008_31-0" class="reference"><A href="#cite_note-Schoenemann2008-31">[29]</A></SUP> Along with the lens and two humors, the cornea is responsible for converging light and aiding the focusing of it on the back of the retina. The cornea protects the eyeball while at the same time accounting for approximately 2/3 of the eye’s total refractive power.<SUP id="cite_ref-32" class="reference"><A href="#cite_note-32">[30]</A></SUP></P>
<P>It is likely that a key reason eyes specialize in detecting a specific, narrow range of wavelengths on the <A href="/wiki/Electromagnetic_spectrum" title="Electromagnetic spectrum">electromagnetic spectrum</A>—the <A href="/wiki/Visible_spectrum" title="Visible spectrum">visible spectrum</A>—is because the earliest species to develop <A href="/wiki/Photosensitivity" title="Photosensitivity">photosensitivity</A> were aquatic, and only two specific wavelength ranges of <A href="/wiki/Electromagnetic_radiation" title="Electromagnetic radiation">electromagnetic radiation</A>, blue and green visible light, can travel through water. This same light-filtering property of water also influenced the photosensitivity of plants.<SUP id="cite_ref-33" class="reference"><A href="#cite_note-33">[31]</A></SUP><SUP id="cite_ref-34" class="reference"><A href="#cite_note-34">[32]</A></SUP><SUP id="cite_ref-35" class="reference"><A href="#cite_note-35">[33]</A></SUP></P>
<H3><SPAN class="mw-headline" id="Lens_formation_and_diversification">Lens formation and diversification</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=6" title="Edit section: Lens formation and diversification">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
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<DIV class="thumbinner" style="width:302px;"><A href="/wiki/File:Focus_in_an_eye.svg" class="image"><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/8/81/Focus_in_an_eye.svg/300px-Focus_in_an_eye.svg.png" width="300" height="101" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/81/Focus_in_an_eye.svg/450px-Focus_in_an_eye.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/81/Focus_in_an_eye.svg/600px-Focus_in_an_eye.svg.png 2x" data-file-width="800" data-file-height="270" /></A>
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Light from a distant object and a near object being focused by changing the curvature of the <A href="/wiki/Lens_(anatomy)" title="Lens (anatomy)">lens</A></DIV>
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<P>In a lensless eye, the light emanating from a distant point hits the back of the eye with about the same size as the eye's <A href="/wiki/Aperture" title="Aperture">aperture</A>. With the addition of a lens this incoming light is concentrated on a smaller surface area, without reducing the overall intensity of the stimulus.<SUP id="cite_ref-Nilsson,_D_1994_8-1" class="reference"><A href="#cite_note-Nilsson,_D_1994-8">[8]</A></SUP> The focal length of an early <A href="/wiki/Lobopod" class="mw-redirect" title="Lobopod">lobopod</A> with lens-containing simple eyes focused the image <I>behind</I> the retina, so while no part of the image could be brought into focus, the intensity of light allowed the organism to see in deeper (and therefore darker) waters.<SUP id="cite_ref-Schoenemann2008_31-1" class="reference"><A href="#cite_note-Schoenemann2008-31">[29]</A></SUP> A subsequent increase of the lens's <A href="/wiki/Refractive_index" title="Refractive index">refractive index</A> probably resulted in an in-focus image being formed.<SUP id="cite_ref-Schoenemann2008_31-2" class="reference"><A href="#cite_note-Schoenemann2008-31">[29]</A></SUP></P>
<P>The development of the lens in camera-type eyes probably followed a different trajectory. The transparent cells over a pinhole eye's aperture split into two layers, with liquid in between.<SUP class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<I><A href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><SPAN title="This claim needs references to reliable sources. (April 2009)">citation needed</SPAN></A></I>]</SUP> The liquid originally served as a circulatory fluid for oxygen, nutrients, wastes, and immune functions, allowing greater total thickness and higher mechanical protection. In addition, multiple interfaces between solids and liquids increase optical power, allowing wider viewing angles and greater imaging resolution. Again, the division of layers may have originated with the shedding of skin; intracellular fluid may infill naturally depending on layer depth.<SUP class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<I><A href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><SPAN title="This claim needs references to reliable sources. (April 2009)">citation needed</SPAN></A></I>]</SUP></P>
<P>Note that this optical layout has not been found, nor is it expected to be found. <A href="/wiki/Fossil" title="Fossil">Fossilization</A> rarely preserves soft tissues, and even if it did, the new humour would almost certainly close as the remains desiccated, or as sediment overburden forced the layers together, making the fossilized eye resemble the previous layout.</P>
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<DIV class="thumbinner" style="width:202px;"><A href="/wiki/File:Krilleyekils.jpg" class="image"><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/64/Krilleyekils.jpg/200px-Krilleyekils.jpg" width="200" height="191" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/64/Krilleyekils.jpg/300px-Krilleyekils.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/64/Krilleyekils.jpg/400px-Krilleyekils.jpg 2x" data-file-width="1574" data-file-height="1505" /></A>
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Compound eye of <A href="/wiki/Antarctic_krill" title="Antarctic krill">Antarctic krill</A></DIV>
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<P>Vertebrate <A href="/wiki/Lens_(anatomy)" title="Lens (anatomy)">lenses</A> are composed of adapted <A href="/wiki/Epithelium" title="Epithelium">epithelial</A> cells which have high concentrations of the protein <A href="/wiki/Crystallin" title="Crystallin">crystallin</A>. These crystallins belong to two major families, the α-crystallins and the βγ-crystallins. Both were categories of proteins originally used for other functions in organisms, but eventually were adapted for the sole purpose of vision in animal eyes.<SUP id="cite_ref-Slingsby,_C._2013_36-0" class="reference"><A href="#cite_note-Slingsby,_C._2013-36">[34]</A></SUP> In the embryo, the lens is living tissue, but the cellular machinery is not transparent so must be removed before the organism can see. Removing the machinery means the lens is composed of dead cells, packed with crystallins. These crystallins are special because they have the unique characteristics required for transparency and function in the lens such as tight packing, resistance to crystallization, and extreme longevity, as they must survive for the entirety of the organism’s life.<SUP id="cite_ref-Slingsby,_C._2013_36-1" class="reference"><A href="#cite_note-Slingsby,_C._2013-36">[34]</A></SUP> The <A href="/wiki/Refractive_index" title="Refractive index">refractive index</A> <A href="/wiki/Gradient_index_optics" class="mw-redirect" title="Gradient index optics">gradient</A> which makes the lens useful is caused by the radial shift in crystallin concentration in different parts of the lens, rather than by the specific type of protein: it is not the presence of crystallin, but the relative distribution of it, that renders the lens useful.<SUP id="cite_ref-37" class="reference"><A href="#cite_note-37">[35]</A></SUP></P>
<P>It is biologically difficult to maintain a transparent layer of cells. Deposition of transparent, nonliving, material eased the need for nutrient supply and waste removal. <A href="/wiki/Trilobites" class="mw-redirect" title="Trilobites">Trilobites</A> used <A href="/wiki/Calcite" title="Calcite">calcite</A>, a mineral which today is known to be used for vision only in a single species of <A href="/wiki/Brittle_star" title="Brittle star">brittle star</A>.<SUP id="cite_ref-38" class="reference"><A href="#cite_note-38">[36]</A></SUP> In other compound eyes<SUP class="noprint Inline-Template" style="white-space:nowrap;">[<I><A href="/wiki/Wikipedia:Verifiability" title="Wikipedia:Verifiability"><SPAN title="The material near this tag needs to be fact-checked with the cited source(s). (February 2009)">verification needed</SPAN></A></I>]</SUP> and camera eyes, the material is <A href="/wiki/Crystallin" title="Crystallin">crystallin</A>. A gap between tissue layers naturally forms a biconvex shape, which is optically and mechanically ideal for substances of normal<SUP class="noprint Inline-Template" style="margin-left:0.1em; white-space:nowrap;">[<I><A href="/wiki/Wikipedia:Please_clarify" title="Wikipedia:Please clarify"><SPAN title="The text near this tag may need clarification or removal of jargon. (March 2017)">clarification needed</SPAN></A></I>]</SUP> refractive index. A biconvex lens confers not only optical resolution, but aperture and low-light ability, as resolution is now decoupled from hole size – which slowly increases again, free from the circulatory constraints.</P>
<P>Independently, a transparent layer and a nontransparent layer may split forward from the lens: a separate <A href="/wiki/Cornea" title="Cornea">cornea</A> and <A href="/wiki/Iris_(anatomy)" title="Iris (anatomy)">iris</A>. (These may happen before or after crystal deposition, or not at all.) Separation of the forward layer again forms a humour, the <A href="/wiki/Aqueous_humour" title="Aqueous humour">aqueous humour</A>. This increases refractive power and again eases circulatory problems. Formation of a nontransparent ring allows more blood vessels, more circulation, and larger eye sizes. This flap around the perimeter of the lens also masks optical imperfections, which are more common at lens edges. The need to mask lens imperfections gradually increases with lens curvature and power, overall lens and eye size, and the resolution and aperture needs of the organism, driven by hunting or survival requirements. This type is now functionally identical to the eye of most vertebrates, including humans. Indeed, "the basic pattern of all vertebrate eyes is similar."<SUP id="cite_ref-Ali&Klyne1985_39-0" class="reference"><A href="#cite_note-Ali&Klyne1985-39">[37]</A></SUP></P>
<H3><SPAN class="mw-headline" id="Other_developments">Other developments</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=7" title="Edit section: Other developments">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H3>
<H4><SPAN class="mw-headline" id="Color_vision">Color vision</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=8" title="Edit section: Color vision">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H4>
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<P>Five classes of visual <A href="/wiki/Opsin" title="Opsin">opsins</A> are found in vertebrates. All but one of these developed prior to the divergence of <A href="/wiki/Cyclostomata" title="Cyclostomata">Cyclostomata</A> and fish.<SUP id="cite_ref-Osorio&Vorobyev_40-0" class="reference"><A href="#cite_note-Osorio&Vorobyev-40">[38]</A></SUP> The five opsin classes are variously adapted depending on the light spectrum encountered. As light travels through water, longer wavelengths, such as reds and yellows, are absorbed more quickly than the shorter <A href="/wiki/Wavelength" title="Wavelength">wavelengths</A> of the greens and blues. This creates a gradient of light as the depth of water increases.<SUP id="cite_ref-Guehmann2015_41-0" class="reference"><A href="#cite_note-Guehmann2015-41">[39]</A></SUP> The visual opsins in fish are more sensitive to the range of light in their habitat and depth. However, land environments do not vary in wavelength composition, so that the opsin sensitivities among land vertebrates does not vary much. This directly contributes to the significant presence of communication colors.<SUP id="cite_ref-Osorio&Vorobyev_40-1" class="reference"><A href="#cite_note-Osorio&Vorobyev-40">[38]</A></SUP> Color vision gives distinct <A href="/wiki/Selection_(biology)" class="mw-redirect" title="Selection (biology)">selective</A> advantages, such as better recognition of predators, food, and mates. Indeed, it is thought<SUP class="noprint Inline-Template" style="white-space:nowrap;">[<I><A href="/wiki/Wikipedia:Manual_of_Style/Words_to_watch#Unsupported_attributions" title="Wikipedia:Manual of Style/Words to watch"><SPAN title="The material near this tag may use weasel words or too-vague attribution. (March 2016)">by whom?</SPAN></A></I>]</SUP> that simple sensory-neural mechanisms may selectively control general behavior patterns, such as escape, foraging, and hiding. Many examples of wavelength-specific behaviors have been identified, in two primary groups: Below 450 nm, associated with direct light, and above 450 nm, associated with reflected light.<SUP id="cite_ref-Menzel1979_42-0" class="reference"><A href="#cite_note-Menzel1979-42">[40]</A></SUP> As opsin molecules were tuned to detect different wavelengths of light, at some point <A href="/wiki/Color_vision" title="Color vision">color vision</A> developed when the photoreceptor cells used differently tuned opsins.<SUP id="cite_ref-photons_28-1" class="reference"><A href="#cite_note-photons-28">[26]</A></SUP> This may have happened at any of the early stages of the eye's evolution, and may have disappeared and reevolved as organisms became predator or prey. Similarly, night and day vision emerged when photoreceptor cells differentiated into rods and cones, respectively.<SUP class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<I><A href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><SPAN title="This claim needs references to reliable sources. (March 2016)">citation needed</SPAN></A></I>]</SUP></P>
<DIV role="note" class="hatnote navigation-not-searchable">Further information: <A href="/wiki/Evolution_of_color_vision" title="Evolution of color vision">Evolution of color vision</A></DIV>
<H4><SPAN class="mw-headline" id="Polarization_vision">Polarization vision</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=9" title="Edit section: Polarization vision">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H4>
<P>As discussed earlier, the properties of light under water differ from those in air. One example of this is the polarization of light. <A href="/wiki/Polarization_(waves)" title="Polarization (waves)">Polarization</A> is the organization of originally disordered light, from the sun, into linear arrangements. This occurs when light passes through slit like filters, as well as when passing into a new medium. Sensitivity to polarized light is especially useful for organisms whose habitats are located more than a few meters under water. In this environment, color vision is less dependable, and therefore a weaker selective factor. While most photoreceptors have the ability to distinguish partially polarized light, terrestrial vertebrates’ membranes are orientated perpendicularly, such that they are insensitive to polarized light.<SUP id="cite_ref-Cronin_et_al_43-0" class="reference"><A href="#cite_note-Cronin_et_al-43">[41]</A></SUP> However, some fish can discern polarized light, demonstrating that they possess some linear photoreceptors. Additionally, cuttlefish are capable of perceiving the polarization of light with high visual fidelity, although they appear to lack any significant capacity for color differentiation.<SUP id="cite_ref-44" class="reference"><A href="#cite_note-44">[42]</A></SUP> Like color vision, sensitivity to polarization can aid in an organism's ability to differentiate surrounding objects and individuals. Because of the marginal reflective interference of polarized light, it is often used for orientation and navigation, as well as distinguishing concealed objects, such as disguised prey.<SUP id="cite_ref-Cronin_et_al_43-1" class="reference"><A href="#cite_note-Cronin_et_al-43">[41]</A></SUP></P>
<H4><SPAN class="mw-headline" id="Focusing_mechanism">Focusing mechanism</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=10" title="Edit section: Focusing mechanism">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H4>
<P>By utilizing the iris sphincter muscle, some species move the lens back and forth, some stretch the lens flatter. Another mechanism regulates focusing chemically and independently of these two, by controlling growth of the eye and maintaining focal length. In addition, the pupil shape can be used to predict the focal system being utilized. A slit pupil can indicate the common multifocal system, while a circular pupil usually specifies a monofocal system. When using a circular form, the pupil will constrict under bright light, increasing the focal length, and will dilate when dark in order to decrease the depth of focus.<SUP id="cite_ref-Malstrom&Kroger_45-0" class="reference"><A href="#cite_note-Malstrom&Kroger-45">[43]</A></SUP> Note that a focusing method is not a requirement. As photographers know, focal errors increase as <A href="/wiki/Aperture" title="Aperture">aperture</A> increases. Thus, countless organisms with small eyes are active in direct sunlight and survive with no focus mechanism at all. As a species grows larger, or transitions to dimmer environments, a means of focusing need only appear gradually.</P>
<H4><SPAN class="mw-headline" id="Location">Location</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=11" title="Edit section: Location">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H4>
<P>Prey generally have eyes on the sides of their head so to have a larger field of view, from which to avoid predators. Predators, however, have eyes in front of their head in order to have better <A href="/wiki/Depth_perception" title="Depth perception">depth perception</A>.<SUP id="cite_ref-BLM_46-0" class="reference"><A href="#cite_note-BLM-46">[44]</A></SUP><SUP id="cite_ref-47" class="reference"><A href="#cite_note-47">[45]</A></SUP> <A href="/wiki/Flatfish" title="Flatfish">Flatfish</A> are predators which lie on their side on the bottom, and have eyes placed asymmetrically on the same side of the head. A <A href="/wiki/Transitional_fossil" title="Transitional fossil">transitional fossil</A> from the common symmetric position is <A href="/wiki/Amphistium" title="Amphistium">Amphistium</A>.</P>
<H2><SPAN class="mw-headline" id="Evolutionary_baggage">Evolutionary baggage</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=12" title="Edit section: Evolutionary baggage">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
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<DIV style=";left:0px; top:0px; width:400px; position:absolute;"><A href="/wiki/File:Evolution_eye.svg" class="image" title="Vertebrates and octopodes developed the camera eye independently. In the vertebrate version the nerve fibers pass in front of the retina, and there is a blind spot where the nerves pass through the retina. In the vertebrate example, 4 represents the blind spot, which is notably absent from the octopus eye. In both vertebrates and octopodes, 1 represents the retina, 2 represents the nerve fibers, and 3 represents the optic nerve."><IMG alt="" src="//upload.wikimedia.org/wikipedia/commons/thumb/9/9b/Evolution_eye.svg/400px-Evolution_eye.svg.png" width="400" height="227" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/9/9b/Evolution_eye.svg/600px-Evolution_eye.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/9/9b/Evolution_eye.svg/800px-Evolution_eye.svg.png 2x" data-file-width="738" data-file-height="419" /></A></DIV>
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<DIV id="annotation_260x15" style="position:absolute; left:260px; top:15px; font-size:15px; font-weight:bold; font-style:italic; line-height:17px;"><SPAN style="background-color:transparent;"><A href="/wiki/Octopus" title="Octopus">Octopus</A></SPAN></DIV>
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<A href="/wiki/Vertebrate" title="Vertebrate">Vertebrates</A> and <A href="/wiki/Octopus" title="Octopus">octopodes</A> developed the camera eye <A href="/wiki/Convergent_evolution" title="Convergent evolution">independently</A>. In the vertebrate version the nerve fibers pass <I>in front</I> of the <A href="/wiki/Retina" title="Retina">retina</A>, and there is a <A href="/wiki/Blind_spot_(vision)" title="Blind spot (vision)">blind spot</A> where the nerves pass through the retina. In the vertebrate example, <B>4</B> represents the <A href="/wiki/Blind_spot_(vision)" title="Blind spot (vision)">blind spot</A>, which is notably absent from the octopus eye. In both vertebrates and octopodes, <B>1</B> represents the <A href="/wiki/Retina" title="Retina">retina</A>, <B>2</B> represents the nerve fibers, and <B>3</B> represents the optic nerve.</DIV>
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<DIV role="note" class="hatnote navigation-not-searchable">Main article: <A href="/wiki/Evolutionary_baggage" title="Evolutionary baggage">Evolutionary baggage</A></DIV>
<P>The eyes of many animals record their evolutionary history in their contemporary anatomy. The vertebrate eye, for instance, is built "backwards and upside down", requiring "photons of light to travel through the cornea, lens, aqueous fluid, blood vessels, ganglion cells, amacrine cells, horizontal cells, and bipolar cells before they reach the light-sensitive rods and cones that transduce the light signal into neural impulses, which are then sent to the visual cortex at the back of the brain for processing into meaningful patterns."<SUP id="cite_ref-48" class="reference"><A href="#cite_note-48">[46]</A></SUP> While such a construct has some drawbacks, it also allows the outer retina of the vertebrates to sustain higher metabolic activities as compared to the non-inverted design.<SUP id="cite_ref-49" class="reference"><A href="#cite_note-49">[47]</A></SUP> It also allowed for the evolution of the <A href="/wiki/Choroid" title="Choroid">choroid layer</A>, including the retinal pigment epithelial (RPE) cells, which play an important role in protecting the photoreceptive cells from photo-oxidative damage.<SUP id="cite_ref-50" class="reference"><A href="#cite_note-50">[48]</A></SUP><SUP id="cite_ref-51" class="reference"><A href="#cite_note-51">[49]</A></SUP></P>
<P>The <A href="/wiki/Cephalopod_eye" title="Cephalopod eye">camera eyes of cephalopods</A>, in contrast, are constructed the "right way out", with the nerves attached to the rear of the retina. This means that they do not have a blind spot. This difference may be accounted for by the origins of eyes; in cephalopods they develop as an <A href="/wiki/Invagination" title="Invagination">invagination</A> of the head surface whereas in vertebrates they originate as an extension of the brain.<SUP id="cite_ref-52" class="reference"><A href="#cite_note-52">[50]</A></SUP></P>
<H2><SPAN class="mw-headline" id="Footnotes">Footnotes</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=13" title="Edit section: Footnotes">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
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<LI id="cite_note-13"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-13"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><A href="/wiki/David_Berlinski" title="David Berlinski">David Berlinski</A>, an intelligent design proponent, questioned the basis of the calculations, and the author of the original paper refuted Berlinski's criticism.</SPAN>
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<LI><SPAN class="reference-text"><CITE class="citation journal"><A href="/wiki/David_Berlinski" title="David Berlinski">Berlinski, David</A> (April 2001). <A rel="nofollow" class="external text" href="http://www.discovery.org/a/1360">"Commentary magazine"</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Commentary+magazine&rft.date=2001-04&rft.au=Berlinski%2C+David&rft_id=http%3A%2F%2Fwww.discovery.org%2Fa%2F1360&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI><CITE class="citation journal">Nilsson, Dan-E. <A rel="nofollow" class="external text" href="http://www.talkreason.org/articles/blurred.cfm#lund">"Beware of Pseudo-science: a response to David Berlinski's attack on my calculation of how long it takes for an eye to evolve"</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.atitle=Beware+of+Pseudo-science%3A+a+response+to+David+Berlinski%27s+attack+on+my+calculation+of+how+long+it+takes+for+an+eye+to+evolve&rft.au=Nilsson%2C+Dan-E.&rft_id=http%3A%2F%2Fwww.talkreason.org%2Farticles%2Fblurred.cfm%23lund&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></LI>
<LI><A rel="nofollow" class="external text" href="https://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html">"Evolution of the Eye" on PBS</A></LI>
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<LI id="cite_note-26"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-26"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">The precise number varies from author to author.</SPAN></LI>
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<H2><SPAN class="mw-headline" id="See_also">See also</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=14" title="Edit section: See also">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
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<LI><A href="/wiki/Ocelloid" title="Ocelloid">Ocelloid</A></LI>
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<H2><SPAN class="mw-headline" id="References">References</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=15" title="Edit section: References">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
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<LI id="cite_note-1"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-1"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">""An important cue for understanding eye evolution is the distinction between different types of photoreceptor cells. Salvini-Plawen and Mayr ( 1977 ) noted a remarkable diversity of photoreceptor cell morphology across the animal kingdom, and suggested that photoreceptors evolved independently numerous times." - Land, M.F. and Nilsson, D.-E., <I>Animal Eyes</I>(2-nd ed.), Oxford University Press, Oxford (2012), p. 7.</SPAN></LI>
<LI id="cite_note-2"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-2"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">""About 65% of genes expressed in the retina of the fruit fly are also active in the retina of the mouse" - Glaeser G., Paulus H. F. - The Evolution of the Eye, Springer (2015), ch. 7, Pax and homology: the third act in the history of evolution- p. 148</SPAN></LI>
<LI id="cite_note-3"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-3"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">" Glaeser G., Paulus H. F. - The Evolution of the Eye, Springer (2015), ch. 7, Pax and homology: the third act in the history of evolution- p. 149</SPAN></LI>
<LI id="cite_note-4"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-4"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Lee, M. S. Y.; Jago, J. B.; Garcia-Bellido, D. C.; Edgecombe, G. E.; Gehling, J. G; Paterson, J. R. (2011). "Modern optics in exceptionally preserved eyes of Early Cambrian arthropods from Australia". <I>Nature</I>. <B>474</B>: 631–634. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1038%2Fnature10097">10.1038/nature10097</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/21720369">21720369</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Nature&rft.atitle=Modern+optics+in+exceptionally+preserved+eyes+of+Early+Cambrian+arthropods+from+Australia&rft.volume=474&rft.pages=631-634&rft.date=2011&rft_id=info%3Adoi%2F10.1038%2Fnature10097&rft_id=info%3Apmid%2F21720369&rft.aulast=Lee&rft.aufirst=M.+S.+Y.&rft.au=Jago%2C+J.+B.&rft.au=Garcia-Bellido%2C+D.+C.&rft.au=Edgecombe%2C+G.+E.&rft.au=Gehling%2C+J.+G&rft.au=Paterson%2C+J.+R.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-origin-5"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-origin_5-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-origin_5-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text"><A href="/wiki/Charles_Darwin" title="Charles Darwin">Darwin, Charles</A> (1859). <I><A href="/wiki/The_Origin_of_Species" class="mw-redirect" title="The Origin of Species">On the Origin of Species</A></I>. London: John Murray.</SPAN></LI>
<LI id="cite_note-6"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-6"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Gehring WJ (2005). "New perspectives on eye development and the evolution of eyes and photoreceptors". <I>J. Hered</I>. <B>96</B> (3): 171–84. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1093%2Fjhered%2Fesi027">10.1093/jhered/esi027</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/15653558">15653558</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=J.+Hered.&rft.atitle=New+perspectives+on+eye+development+and+the+evolution+of+eyes+and+photoreceptors&rft.volume=96&rft.issue=3&rft.pages=171-84&rft.date=2005&rft_id=info%3Adoi%2F10.1093%2Fjhered%2Fesi027&rft_id=info%3Apmid%2F15653558&rft.au=Gehring+WJ&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-7"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-7"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Nilsson, D.-E. (2013). "Eye evolution and its functional basis". <I>Visual Neuroscience</I>. <B>30</B>: 5–20. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1017%2Fs0952523813000035">10.1017/s0952523813000035</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Visual+Neuroscience&rft.atitle=Eye+evolution+and+its+functional+basis&rft.volume=30&rft.pages=5-20&rft.date=2013&rft_id=info%3Adoi%2F10.1017%2Fs0952523813000035&rft.aulast=Nilsson&rft.aufirst=D.-E.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Nilsson,_D_1994-8"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Nilsson,_D_1994_8-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Nilsson,_D_1994_8-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Nilsson, D.-E.; Pelger, S. (1994). "A pessimistic estimate of the time required for an eye to evolve". <I>Proceedings of the Royal Society B: Biological Sciences</I>. <B>256</B>: 53–58. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1098%2Frspb.1994.0048">10.1098/rspb.1994.0048</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/8008757">8008757</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Proceedings+of+the+Royal+Society+B%3A+Biological+Sciences&rft.atitle=A+pessimistic+estimate+of+the+time+required+for+an+eye+to+evolve&rft.volume=256&rft.pages=53-58&rft.date=1994&rft_id=info%3Adoi%2F10.1098%2Frspb.1994.0048&rft_id=info%3Apmid%2F8008757&rft.aulast=Nilsson&rft.aufirst=D.-E.&rft.au=Pelger%2C+S.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-9"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-9"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Young, G. C. (2008). "Early evolution of the vertebrate eye – fossil evidence". <I>Evo Edu Outreach</I>. <B>1</B>: 427–438. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1007%2Fs12052-008-0087-y">10.1007/s12052-008-0087-y</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Evo+Edu+Outreach&rft.atitle=Early+evolution+of+the+vertebrate+eye+%E2%80%93+fossil+evidence&rft.volume=1&rft.pages=427-438&rft.date=2008&rft_id=info%3Adoi%2F10.1007%2Fs12052-008-0087-y&rft.aulast=Young&rft.aufirst=G.+C.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Parker2009-10"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-Parker2009_10-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Parker, A. R. (2009). "On the origin of optics". <I>Optics & Laser Technology</I>. <B>43</B> (2): 323–329. <A href="/wiki/Bibcode" title="Bibcode">Bibcode</A>:<A rel="nofollow" class="external text" href="http://adsabs.harvard.edu/abs/2011OptLT..43..323P">2011OptLT..43..323P</A>. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1016%2Fj.optlastec.2008.12.020">10.1016/j.optlastec.2008.12.020</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Optics+%26+Laser+Technology&rft.atitle=On+the+origin+of+optics&rft.volume=43&rft.issue=2&rft.pages=323-329&rft.date=2009&rft_id=info%3Adoi%2F10.1016%2Fj.optlastec.2008.12.020&rft_id=info%3Abibcode%2F2011OptLT..43..323P&rft.aulast=Parker&rft.aufirst=A.+R.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-parker2003-11"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-parker2003_11-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation book">Parker, Andrew (2003). <I>In the Blink of an Eye: How Vision Sparked the Big Bang of Evolution</I>. Cambridge, MA: Perseus Pub. <A href="/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</A> <A href="/wiki/Special:BookSources/0-7382-0607-5" title="Special:BookSources/0-7382-0607-5">0-7382-0607-5</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=In+the+Blink+of+an+Eye%3A+How+Vision+Sparked+the+Big+Bang+of+Evolution&rft.place=Cambridge%2C+MA&rft.pub=Perseus+Pub.&rft.date=2003&rft.isbn=0-7382-0607-5&rft.aulast=Parker&rft.aufirst=Andrew&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Nilsson1994-12"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Nilsson1994_12-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Nilsson1994_12-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Nilsson, D-E; Pelger S (1994). "A pessimistic estimate of the time required for an eye to evolve". <I><A href="/wiki/Proceedings_of_the_Royal_Society_B" class="mw-redirect" title="Proceedings of the Royal Society B">Proceedings of the Royal Society B</A></I>. <B>256</B> (1345): 53–58. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1098%2Frspb.1994.0048">10.1098/rspb.1994.0048</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/8008757">8008757</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Proceedings+of+the+Royal+Society+B&rft.atitle=A+pessimistic+estimate+of+the+time+required+for+an+eye+to+evolve&rft.volume=256&rft.issue=1345&rft.pages=53-58&rft.date=1994&rft_id=info%3Adoi%2F10.1098%2Frspb.1994.0048&rft_id=info%3Apmid%2F8008757&rft.au=Nilsson%2C+D-E&rft.au=Pelger+S&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Nilsson1996-14"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-Nilsson1996_14-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Nilsson, D. E. (1996). "Eye ancestry: old genes for new eyes". <I>Current Biology</I>. <B>6</B> (1): 39–42. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1016%2FS0960-9822%2802%2900417-7">10.1016/S0960-9822(02)00417-7</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/8805210">8805210</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Current+Biology&rft.atitle=Eye+ancestry%3A+old+genes+for+new+eyes&rft.volume=6&rft.issue=1&rft.pages=39-42&rft.date=1996&rft_id=info%3Adoi%2F10.1016%2FS0960-9822%2802%2900417-7&rft_id=info%3Apmid%2F8805210&rft.aulast=Nilsson&rft.aufirst=D.+E.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-15"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-15"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Zinovieva, R.; Piatigorsky, J.; Tomarev, S. I. (1999). "O-Crystallin, arginine kinase and ferritin from the octopus lens". <I>Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology</I>. <B>1431</B> (2): 512–517. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1016%2FS0167-4838%2899%2900066-7">10.1016/S0167-4838(99)00066-7</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Biochimica+et+Biophysica+Acta+%28BBA%29+-+Protein+Structure+and+Molecular+Enzymology&rft.atitle=O-Crystallin%2C+arginine+kinase+and+ferritin+from+the+octopus+lens&rft.volume=1431&rft.issue=2&rft.pages=512-517&rft.date=1999&rft_id=info%3Adoi%2F10.1016%2FS0167-4838%2899%2900066-7&rft.aulast=Zinovieva&rft.aufirst=R.&rft.au=Piatigorsky%2C+J.&rft.au=Tomarev%2C+S.+I.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Scotland2010-16"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Scotland2010_16-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Scotland2010_16-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Scotland, R. W. (2010). "Deep homology: A view from systematics". <I>BioEssays</I>. <B>32</B> (5): 438–449. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1002%2Fbies.200900175">10.1002/bies.200900175</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/20394064">20394064</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=BioEssays&rft.atitle=Deep+homology%3A+A+view+from+systematics&rft.volume=32&rft.issue=5&rft.pages=438-449&rft.date=2010&rft_id=info%3Adoi%2F10.1002%2Fbies.200900175&rft_id=info%3Apmid%2F20394064&rft.aulast=Scotland&rft.aufirst=R.+W.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-17"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-17"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Ramirez, MD; Pairett, AN; Pankey, MS; Serb, JM; Speiser, DI; Swafford, AJ; Oakley, TH (26 October 2016). "The last common ancestor of most bilaterian animals possessed at least 9 opsins". <I>Genome Biology and Evolution</I>: evw248. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1093%2Fgbe%2Fevw248">10.1093/gbe/evw248</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Genome+Biology+and+Evolution&rft.atitle=The+last+common+ancestor+of+most+bilaterian+animals+possessed+at+least+9+opsins&rft.pages=evw248&rft.date=2016-10-26&rft_id=info%3Adoi%2F10.1093%2Fgbe%2Fevw248&rft.aulast=Ramirez&rft.aufirst=MD&rft.au=Pairett%2C+AN&rft.au=Pankey%2C+MS&rft.au=Serb%2C+JM&rft.au=Speiser%2C+DI&rft.au=Swafford%2C+AJ&rft.au=Oakley%2C+TH&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-18"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-18"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Yoshida, Masa-aki; Yura, Kei; Ogura, Atsushi (5 March 2014). <A rel="nofollow" class="external text" href="http://www.nature.com/srep/2014/140305/srep04256/full/srep04256.html">"Cephalopod eye evolution was modulated by the acquisition of Pax-6 splicing variants"</A>. <I>Scientific Reports</I>. nature.com. <B>4</B>. <A href="/wiki/Bibcode" title="Bibcode">Bibcode</A>:<A rel="nofollow" class="external text" href="http://adsabs.harvard.edu/abs/2014NatSR...4E4256Y">2014NatSR...4E4256Y</A>. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1038%2Fsrep04256">10.1038/srep04256</A>. <A href="/wiki/PubMed_Central" title="PubMed Central">PMC</A> <SPAN class="plainlinks"><A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC3942700">3942700</A> <IMG alt="Freely accessible" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png" title="Freely accessible" width="9" height="14" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/14px-Lock-green.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/18px-Lock-green.svg.png 2x" data-file-width="512" data-file-height="813" /></SPAN>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/24594543">24594543</A><SPAN class="reference-accessdate">. Retrieved <SPAN class="nowrap">June 30,</SPAN> 2014</SPAN>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Scientific+Reports&rft.atitle=Cephalopod+eye+evolution+was+modulated+by+the+acquisition+of+Pax-6+splicing+variants&rft.volume=4&rft.date=2014-03-05&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3942700&rft_id=info%3Apmid%2F24594543&rft_id=info%3Adoi%2F10.1038%2Fsrep04256&rft_id=info%3Abibcode%2F2014NatSR...4E4256Y&rft.aulast=Yoshida&rft.aufirst=Masa-aki&rft.au=Yura%2C+Kei&rft.au=Ogura%2C+Atsushi&rft_id=http%3A%2F%2Fwww.nature.com%2Fsrep%2F2014%2F140305%2Fsrep04256%2Ffull%2Fsrep04256.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-19"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-19"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Halder, G.; Callaerts, P.; Gehring, W. J. (1995). "New perspectives on eye evolution". <I>Current Opinion in Genetics & Development</I>. <B>5</B> (5): 602–609. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1016%2F0959-437X%2895%2980029-8">10.1016/0959-437X(95)80029-8</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/8664548">8664548</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Current+Opinion+in+Genetics+%26+Development&rft.atitle=New+perspectives+on+eye+evolution&rft.volume=5&rft.issue=5&rft.pages=602-609&rft.date=1995&rft_id=info%3Adoi%2F10.1016%2F0959-437X%2895%2980029-8&rft_id=info%3Apmid%2F8664548&rft.aulast=Halder&rft.aufirst=G.&rft.au=Callaerts%2C+P.&rft.au=Gehring%2C+W.+J.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-20"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-20"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Halder, G.; Callaerts, P.; Gehring, W. (1995). "Induction of ectopic eyes by targeted expression of the eyeless gene in Drosophila". <I>Science</I>. <B>267</B> (5205): 1788–92. <A href="/wiki/Bibcode" title="Bibcode">Bibcode</A>:<A rel="nofollow" class="external text" href="http://adsabs.harvard.edu/abs/1995Sci...267.1788H">1995Sci...267.1788H</A>. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1126%2Fscience.7892602">10.1126/science.7892602</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/7892602">7892602</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Science&rft.atitle=Induction+of+ectopic+eyes+by+targeted+expression+of+the+eyeless+gene+in+Drosophila&rft.volume=267&rft.issue=5205&rft.pages=1788-92&rft.date=1995&rft_id=info%3Apmid%2F7892602&rft_id=info%3Adoi%2F10.1126%2Fscience.7892602&rft_id=info%3Abibcode%2F1995Sci...267.1788H&rft.aulast=Halder&rft.aufirst=G.&rft.au=Callaerts%2C+P.&rft.au=Gehring%2C+W.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-21"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-21"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Tomarev, S. I.; Callaerts, P.; Kos, L.; Zinovieva, R.; Halder, G.; Gehring, W.; Piatigorsky, J. (1997). <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC20103">"Squid Pax-6 and eye development"</A>. <I>Proceedings of the National Academy of Sciences of the United States of America</I>. <B>94</B> (6): 2421–2426. <A href="/wiki/Bibcode" title="Bibcode">Bibcode</A>:<A rel="nofollow" class="external text" href="http://adsabs.harvard.edu/abs/1997PNAS...94.2421T">1997PNAS...94.2421T</A>. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1073%2Fpnas.94.6.2421">10.1073/pnas.94.6.2421</A>. <A href="/wiki/PubMed_Central" title="PubMed Central">PMC</A> <SPAN class="plainlinks"><A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC20103">20103</A> <IMG alt="Freely accessible" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png" title="Freely accessible" width="9" height="14" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/14px-Lock-green.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/18px-Lock-green.svg.png 2x" data-file-width="512" data-file-height="813" /></SPAN>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/9122210">9122210</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Proceedings+of+the+National+Academy+of+Sciences+of+the+United+States+of+America&rft.atitle=Squid+Pax-6+and+eye+development&rft.volume=94&rft.issue=6&rft.pages=2421-2426&rft.date=1997&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC20103&rft_id=info%3Apmid%2F9122210&rft_id=info%3Adoi%2F10.1073%2Fpnas.94.6.2421&rft_id=info%3Abibcode%2F1997PNAS...94.2421T&rft.aulast=Tomarev&rft.aufirst=S.+I.&rft.au=Callaerts%2C+P.&rft.au=Kos%2C+L.&rft.au=Zinovieva%2C+R.&rft.au=Halder%2C+G.&rft.au=Gehring%2C+W.&rft.au=Piatigorsky%2C+J.&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC20103&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Gehring-22"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Gehring_22-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Gehring_22-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Gehring, W. J. (13 January 2005). <A rel="nofollow" class="external text" href="http://jhered.oxfordjournals.org/cgi/content/full/96/3/171">"New Perspectives on Eye Development and the Evolution of Eyes and Photoreceptors"</A> <SPAN style="font-size:85%;">(Full text)</SPAN>. <I>Journal of Heredity</I>. Oxford Journals. <B>96</B> (3): 171–184. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1093%2Fjhered%2Fesi027">10.1093/jhered/esi027</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/15653558">15653558</A><SPAN class="reference-accessdate">. Retrieved <SPAN class="nowrap">2008-04-26</SPAN></SPAN>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Journal+of+Heredity&rft.atitle=New+Perspectives+on+Eye+Development+and+the+Evolution+of+Eyes+and+Photoreceptors&rft.volume=96&rft.issue=3&rft.pages=171-184&rft.date=2005-01-13&rft_id=info%3Adoi%2F10.1093%2Fjhered%2Fesi027&rft_id=info%3Apmid%2F15653558&rft.aulast=Gehring&rft.aufirst=W.+J.&rft_id=http%3A%2F%2Fjhered.oxfordjournals.org%2Fcgi%2Fcontent%2Ffull%2F96%2F3%2F171&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Land1992-23"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Land1992_23-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Land1992_23-1"><SUP><I><B>b</B></I></SUP></A> <A href="#cite_ref-Land1992_23-2"><SUP><I><B>c</B></I></SUP></A> <A href="#cite_ref-Land1992_23-3"><SUP><I><B>d</B></I></SUP></A> <A href="#cite_ref-Land1992_23-4"><SUP><I><B>e</B></I></SUP></A> <A href="#cite_ref-Land1992_23-5"><SUP><I><B>f</B></I></SUP></A> <A href="#cite_ref-Land1992_23-6"><SUP><I><B>g</B></I></SUP></A> <A href="#cite_ref-Land1992_23-7"><SUP><I><B>h</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">M F Land; R D Fernald (1992). "The Evolution of Eyes". <I>Annual Review of Neuroscience</I>. <B>15</B>: 1–29. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1146%2Fannurev.ne.15.030192.000245">10.1146/annurev.ne.15.030192.000245</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/1575438">1575438</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Annual+Review+of+Neuroscience&rft.atitle=The+Evolution+of+Eyes&rft.volume=15&rft.pages=1-29&rft.date=1992&rft_id=info%3Adoi%2F10.1146%2Fannurev.ne.15.030192.000245&rft_id=info%3Apmid%2F1575438&rft.au=M+F+Land&rft.au=R+D+Fernald&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Autrum1979-24"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-Autrum1979_24-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation book">Autrum, H (1979). "Introduction". In H. Autrum. <I>Comparative Physiology and Evolution of Vision in Invertebrates- A: Invertebrate Photoreceptors</I>. Handbook of Sensory Physiology. VII/6A. New York: Springer-Verlag. pp. 6–9. <A href="/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</A> <A href="/wiki/Special:BookSources/3-540-08837-7" title="Special:BookSources/3-540-08837-7">3-540-08837-7</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Introduction&rft.btitle=Comparative+Physiology+and+Evolution+of+Vision+in+Invertebrates-+A%3A+Invertebrate+Photoreceptors&rft.place=New+York&rft.series=Handbook+of+Sensory+Physiology&rft.pages=6-9&rft.pub=Springer-Verlag&rft.date=1979&rft.isbn=3-540-08837-7&rft.au=Autrum%2C+H&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Arendt2004-25"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-Arendt2004_25-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Arendt, D.; Tessmar-Raible, K.; Snyman, H.; Dorresteijn, A.W.; Wittbrodt, J. (29 October 2004). "Ciliary Photoreceptors with a Vertebrate-Type Opsin in an Invertebrate Brain". <I>Science</I>. <B>306</B> (5697): 869–871. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1126%2Fscience.1099955">10.1126/science.1099955</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/15514158">15514158</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Science&rft.atitle=Ciliary+Photoreceptors+with+a+Vertebrate-Type+Opsin+in+an+Invertebrate+Brain&rft.volume=306&rft.issue=5697&rft.pages=869-871&rft.date=2004-10-29&rft_id=info%3Adoi%2F10.1126%2Fscience.1099955&rft_id=info%3Apmid%2F15514158&rft.aulast=Arendt&rft.aufirst=D.&rft.au=Tessmar-Raible%2C+K.&rft.au=Snyman%2C+H.&rft.au=Dorresteijn%2C+A.W.&rft.au=Wittbrodt%2C+J.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-ee-27"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-ee_27-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><A rel="nofollow" class="external text" href="http://library.thinkquest.org/28030/eyeevo.htm">Eye-Evolution?</A> <A rel="nofollow" class="external text" href="https://web.archive.org/web/20120915061324/http://library.thinkquest.org/28030/eyeevo.htm">Archived</A> 15 September 2012 at the <A href="/wiki/Wayback_Machine" title="Wayback Machine">Wayback Machine</A>.</SPAN></LI>
<LI id="cite_note-photons-28"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-photons_28-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-photons_28-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text">Fernald, Russell D. (2001). <A rel="nofollow" class="external text" href="http://www.karger.com/gazette/64/fernald/art_1_3.htm">The Evolution of Eyes: How Do Eyes Capture Photons?</A> <I>Karger Gazette</I> 64: "The Eye in Focus".</SPAN></LI>
<LI id="cite_note-29"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-29"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Conway-Morris, S. (1998). <I>The Crucible of Creation</I>. Oxford: Oxford University Press.</SPAN></LI>
<LI id="cite_note-dawkins-30"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-dawkins_30-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><A href="/wiki/Richard_Dawkins" title="Richard Dawkins">Dawkins, Richard</A> (1986). <I><A href="/wiki/The_Blind_Watchmaker" title="The Blind Watchmaker">The Blind Watchmaker</A></I>.</SPAN></LI>
<LI id="cite_note-Schoenemann2008-31"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Schoenemann2008_31-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Schoenemann2008_31-1"><SUP><I><B>b</B></I></SUP></A> <A href="#cite_ref-Schoenemann2008_31-2"><SUP><I><B>c</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Schoenemann, B.; Liu, J. N.; Shu, D. G.; Han, J.; Zhang, Z. F. (2008). "A miniscule optimized visual system in the Lower Cambrian". <I>Lethaia</I>. <B>42</B> (3): 265–273. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1111%2Fj.1502-3931.2008.00138.x">10.1111/j.1502-3931.2008.00138.x</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Lethaia&rft.atitle=A+miniscule+optimized+visual+system+in+the+Lower+Cambrian&rft.volume=42&rft.issue=3&rft.pages=265-273&rft.date=2008&rft_id=info%3Adoi%2F10.1111%2Fj.1502-3931.2008.00138.x&rft.aulast=Schoenemann&rft.aufirst=B.&rft.au=Liu%2C+J.+N.&rft.au=Shu%2C+D.+G.&rft.au=Han%2C+J.&rft.au=Zhang%2C+Z.+F.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-32"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-32"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Ali, M.A. and M. A. Klyne. 1985. Vision in vertebrates. New York: Plenum Press</SPAN></LI>
<LI id="cite_note-33"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-33"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Fernald, Russell D. (2001). <A rel="nofollow" class="external text" href="http://www.karger.com/gazette/64/fernald/art_1_1.htm">The Evolution of Eyes: Why Do We See What We See?</A> <I>Karger Gazette</I> 64: "The Eye in Focus".</SPAN></LI>
<LI id="cite_note-34"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-34"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Fernald, Russell D. (1998). <I>Aquatic Adaptations in Fish Eyes</I>. New York, Springer.</SPAN></LI>
<LI id="cite_note-35"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-35"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Fernald RD (1997). "The evolution of eyes". <I>Brain Behav. Evol</I>. <B>50</B> (4): 253–9. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1159%2F000113339">10.1159/000113339</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/9310200">9310200</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Brain+Behav.+Evol.&rft.atitle=The+evolution+of+eyes&rft.volume=50&rft.issue=4&rft.pages=253-9&rft.date=1997&rft_id=info%3Adoi%2F10.1159%2F000113339&rft_id=info%3Apmid%2F9310200&rft.au=Fernald+RD&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Slingsby,_C._2013-36"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Slingsby,_C._2013_36-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Slingsby,_C._2013_36-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Slingsby, C.; Wistow, G. J.; Clark, A. R. (2013). "Evolution of crystallins for a role in the vertebrate eye lens". <I>Protein Science</I>. <B>22</B>: 367–380. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1002%2Fpro.2229">10.1002/pro.2229</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Protein+Science&rft.atitle=Evolution+of+crystallins+for+a+role+in+the+vertebrate+eye+lens&rft.volume=22&rft.pages=367-380&rft.date=2013&rft_id=info%3Adoi%2F10.1002%2Fpro.2229&rft.aulast=Slingsby&rft.aufirst=C.&rft.au=Wistow%2C+G.+J.&rft.au=Clark%2C+A.+R.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-37"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-37"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Fernald, Russell D. (2001). <A rel="nofollow" class="external text" href="http://www.karger.com/gazette/64/fernald/art_1_4">The Evolution of Eyes: Where Do Lenses Come From?</A> <I>Karger Gazette</I> 64: "The Eye in Focus".</SPAN></LI>
<LI id="cite_note-38"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-38"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Burgess, Daniel S. (2001). <A rel="nofollow" class="external text" href="http://www.photonics.com/Article.aspx?AID=10912.htm">Brittle Star Features Calcite Lenses</A>, <I>Photonics Spectra</I></SPAN></LI>
<LI id="cite_note-Ali&Klyne1985-39"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-Ali&Klyne1985_39-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation book">Ali, Mohamed Ather; Klyne, M. A. (1985). <I>Vision in Vertebrates</I>. New York: Plenum Press. p. 1. <A href="/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</A> <A href="/wiki/Special:BookSources/0-306-42065-1" title="Special:BookSources/0-306-42065-1">0-306-42065-1</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Vision+in+Vertebrates&rft.place=New+York&rft.pages=1&rft.pub=Plenum+Press&rft.date=1985&rft.isbn=0-306-42065-1&rft.aulast=Ali&rft.aufirst=Mohamed+Ather&rft.au=Klyne%2C+M.+A.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Osorio&Vorobyev-40"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Osorio&Vorobyev_40-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Osorio&Vorobyev_40-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Osorio, D; Vorobyev, M (2005). "Photo-receptor spectral sensitivities in terrestrial animals: adaptations for luminescence and color vision". <I>Proc. R. Soc. B</I>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Proc.+R.+Soc.+B&rft.atitle=Photo-receptor+spectral+sensitivities+in+terrestrial+animals%3A+adaptations+for+luminescence+and+color+vision&rft.date=2005&rft.aulast=Osorio&rft.aufirst=D&rft.au=Vorobyev%2C+M&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Guehmann2015-41"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-Guehmann2015_41-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Gühmann, Martin; Jia, Huiyong; Randel, Nadine; Verasztó, Csaba; Bezares-Calderón, Luis A.; Michiels, Nico K.; Yokoyama, Shozo; Jékely, Gáspár (August 2015). <A rel="nofollow" class="external text" href="http://www.sciencedirect.com/science/article/pii/S0960982215008209">"Spectral Tuning of Phototaxis by a Go-Opsin in the Rhabdomeric Eyes of Platynereis"</A>. <I>Current Biology</I>. <B>25</B> (17): 2265–2271. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1016%2Fj.cub.2015.07.017">10.1016/j.cub.2015.07.017</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/26255845">26255845</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Current+Biology&rft.atitle=Spectral+Tuning+of+Phototaxis+by+a+Go-Opsin+in+the+Rhabdomeric+Eyes+of+Platynereis&rft.volume=25&rft.issue=17&rft.pages=2265-2271&rft.date=2015-08&rft_id=info%3Adoi%2F10.1016%2Fj.cub.2015.07.017&rft_id=info%3Apmid%2F26255845&rft.aulast=G%C3%BChmann&rft.aufirst=Martin&rft.au=Jia%2C+Huiyong&rft.au=Randel%2C+Nadine&rft.au=Veraszt%C3%B3%2C+Csaba&rft.au=Bezares-Calder%C3%B3n%2C+Luis+A.&rft.au=Michiels%2C+Nico+K.&rft.au=Yokoyama%2C+Shozo&rft.au=J%C3%A9kely%2C+G%C3%A1sp%C3%A1r&rft_id=http%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0960982215008209&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Menzel1979-42"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-Menzel1979_42-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation book">Menzel, Randolf (1979). "Spectral Sensitivity and Color Vision in Invertebrates". In H. Autrum. <I>Comparative Physiology and Evolution of Vision in Invertebrates- A: Invertebrate Photo-receptors</I>. Handbook of Sensory Physiology. VII/6A. New York: Springer-Verlag. pp. 504–506; 551–558. <A href="/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</A> <A href="/wiki/Special:BookSources/3-540-08837-7" title="Special:BookSources/3-540-08837-7">3-540-08837-7</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Spectral+Sensitivity+and+Color+Vision+in+Invertebrates&rft.btitle=Comparative+Physiology+and+Evolution+of+Vision+in+Invertebrates-+A%3A+Invertebrate+Photo-receptors&rft.place=New+York&rft.series=Handbook+of+Sensory+Physiology&rft.pages=504-506%3B+551-558&rft.pub=Springer-Verlag&rft.date=1979&rft.isbn=3-540-08837-7&rft.au=Menzel%2C+Randolf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Cronin_et_al-43"><SPAN class="mw-cite-backlink">^ <A href="#cite_ref-Cronin_et_al_43-0"><SPAN class="cite-accessibility-label">Jump up to: </SPAN><SUP><I><B>a</B></I></SUP></A> <A href="#cite_ref-Cronin_et_al_43-1"><SUP><I><B>b</B></I></SUP></A></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Cronin, T; Shashar, N; Caldwell, R; Marshall, J; Cheroske, A; Chiou, T (2003). "Polarization vision and its role in biological signaling". <I>Integr. Comp. Biol</I>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Integr.+Comp.+Biol.&rft.atitle=Polarization+vision+and+its+role+in+biological+signaling&rft.date=2003&rft.aulast=Cronin&rft.aufirst=T&rft.au=Shashar%2C+N&rft.au=Caldwell%2C+R&rft.au=Marshall%2C+J&rft.au=Cheroske%2C+A&rft.au=Chiou%2C+T&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-44"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-44"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Mäthger, Lydia M.; Barbosa, Alexandra; Miner, Simon; Hanlon, Roger T. (2006-05-01). <A rel="nofollow" class="external text" href="http://www.sciencedirect.com/science/article/pii/S0042698905004943">"Color blindness and contrast perception in cuttlefish (Sepia officinalis) determined by a visual sensorimotor assay"</A>. <I>Vision Research</I>. <B>46</B> (11): 1746–1753. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1016%2Fj.visres.2005.09.035">10.1016/j.visres.2005.09.035</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/16376404">16376404</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Vision+Research&rft.atitle=Color+blindness+and+contrast+perception+in+cuttlefish+%28Sepia+officinalis%29+determined+by+a+visual+sensorimotor+assay&rft.volume=46&rft.issue=11&rft.pages=1746-1753&rft.date=2006-05-01&rft_id=info%3Adoi%2F10.1016%2Fj.visres.2005.09.035&rft_id=info%3Apmid%2F16376404&rft.aulast=M%C3%A4thger&rft.aufirst=Lydia+M.&rft.au=Barbosa%2C+Alexandra&rft.au=Miner%2C+Simon&rft.au=Hanlon%2C+Roger+T.&rft_id=http%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0042698905004943&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-Malstrom&Kroger-45"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-Malstrom&Kroger_45-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Malstrom, T; Kroger, R (2006). "pupil shape and lens optics in the eyes of terrestrial vertebrates". <I>The Journal of Experimental Biology</I>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=The+Journal+of+Experimental+Biology&rft.atitle=pupil+shape+and+lens+optics+in+the+eyes+of+terrestrial+vertebrates&rft.date=2006&rft.aulast=Malstrom&rft.aufirst=T&rft.au=Kroger%2C+R&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-BLM-46"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-BLM_46-0"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation web"><A rel="nofollow" class="external text" href="http://www.blm.gov/id/st/en/prog/wildlife/carnivores.html">"Carnivores"</A>. U.S. Department of the Interior, Bureau of Land Management. 2009-12-14<SPAN class="reference-accessdate">. Retrieved <SPAN class="nowrap">2011-03-28</SPAN></SPAN>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Carnivores&rft.pub=U.S.+Department+of+the+Interior%2C+Bureau+of+Land+Management&rft.date=2009-12-14&rft_id=http%3A%2F%2Fwww.blm.gov%2Fid%2Fst%2Fen%2Fprog%2Fwildlife%2Fcarnivores.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-47"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-47"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation web">Boroditsky, Lera (1999-06-24). <A rel="nofollow" class="external text" href="http://www-psych.stanford.edu/~lera/psych115s/notes/lecture2/">"Light & Eyes: Lecture Notes"</A>. <I>Lecture Notes</I>. <A href="/wiki/Stanford" class="mw-redirect" title="Stanford">Stanford</A><SPAN class="reference-accessdate">. Retrieved <SPAN class="nowrap">11 May</SPAN> 2010</SPAN>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=Lecture+Notes&rft.atitle=Light+%26+Eyes%3A+Lecture+Notes&rft.date=1999-06-24&rft.aulast=Boroditsky&rft.aufirst=Lera&rft_id=http%3A%2F%2Fwww-psych.stanford.edu%2F~lera%2Fpsych115s%2Fnotes%2Flecture2%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
<LI id="cite_note-48"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-48"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Dr. Michael Shermer, as quoted by Christopher Hitchens in his book "God is Not Great" (pg.82)</SPAN></LI>
<LI id="cite_note-49"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-49"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Reichenbach A, Bringmann A. (2010). <I>Müller cells in the healthy and diseased retina</I>. New York: Springer. pp 15 - 20.</SPAN></LI>
<LI id="cite_note-50"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-50"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><A rel="nofollow" class="external free" href="http://www.photobiology.info/Rozanowska.html">http://www.photobiology.info/Rozanowska.html</A></SPAN></LI>
<LI id="cite_note-51"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-51"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text">Diagrammatic representation of disc shedding and phagosome retrieval into the pigment epithelial cell.<A rel="nofollow" class="external autonumber" href="http://webvision.med.utah.edu/imageswv/photphag.jpeg">[1]</A></SPAN></LI>
<LI id="cite_note-52"><SPAN class="mw-cite-backlink"><B><A href="#cite_ref-52"><SPAN class="cite-accessibility-label">Jump up </SPAN>^</A></B></SPAN> <SPAN class="reference-text"><CITE class="citation journal">Serb, Jeanne M.; Eernisse, Douglas J. (2008-09-25). <A rel="nofollow" class="external text" href="https://link.springer.com/article/10.1007/s12052-008-0084-1">"Charting Evolution's Trajectory: Using Molluscan Eye Diversity to Understand Parallel and Convergent Evolution"</A>. <I>Evolution: Education and Outreach</I>. <B>1</B> (4): 439–447. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1007%2Fs12052-008-0084-1">10.1007/s12052-008-0084-1</A>. <A href="/wiki/International_Standard_Serial_Number" title="International Standard Serial Number">ISSN</A> <A rel="nofollow" class="external text" href="//www.worldcat.org/issn/1936-6426">1936-6426</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Evolution%3A+Education+and+Outreach&rft.atitle=Charting+Evolution%E2%80%99s+Trajectory%3A+Using+Molluscan+Eye+Diversity+to+Understand+Parallel+and+Convergent+Evolution&rft.volume=1&rft.issue=4&rft.pages=439-447&rft.date=2008-09-25&rft_id=info%3Adoi%2F10.1007%2Fs12052-008-0084-1&rft.issn=1936-6426&rft.aulast=Serb&rft.aufirst=Jeanne+M.&rft.au=Eernisse%2C+Douglas+J.&rft_id=https%3A%2F%2Flink.springer.com%2Farticle%2F10.1007%2Fs12052-008-0084-1&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></SPAN></LI>
</OL>
</DIV>
<H2><SPAN class="mw-headline" id="Further_reading">Further reading</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=16" title="Edit section: Further reading">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<DIV class="refbegin" style="">
<UL>
<LI><CITE class="citation journal">Lamb TD, Collin SP, Pugh EN (December 2007). <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC3143066">"Evolution of the vertebrate eye: opsins, photoreceptors, retina and eye cup"</A>. <I>Nat. Rev. Neurosci</I>. <B>8</B> (12): 960–76. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1038%2Fnrn2283">10.1038/nrn2283</A>. <A href="/wiki/PubMed_Central" title="PubMed Central">PMC</A> <SPAN class="plainlinks"><A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC3143066">3143066</A> <IMG alt="Freely accessible" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png" title="Freely accessible" width="9" height="14" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/14px-Lock-green.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/18px-Lock-green.svg.png 2x" data-file-width="512" data-file-height="813" /></SPAN>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/18026166">18026166</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Nat.+Rev.+Neurosci.&rft.atitle=Evolution+of+the+vertebrate+eye%3A+opsins%2C+photoreceptors%2C+retina+and+eye+cup&rft.volume=8&rft.issue=12&rft.pages=960-76&rft.date=2007-12&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3143066&rft_id=info%3Apmid%2F18026166&rft_id=info%3Adoi%2F10.1038%2Fnrn2283&rft.aulast=Lamb&rft.aufirst=TD&rft.au=Collin%2C+SP&rft.au=Pugh%2C+EN&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3143066&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN> <A rel="nofollow" class="external text" href="http://www.nature.com/nrn/journal/v8/n12/fig_tab/nrn2283_F4.html">Illustration.</A> <A rel="nofollow" class="external text" href="http://scienceblogs.com/pharyngula/2007/12/21/evolution-of-vertebrate-eyes">Review</A></LI>
<LI><CITE class="citation journal">Lamb, TD (2011). <A rel="nofollow" class="external text" href="http://physics.okstate.edu/axie/courses/4313/2012fall/C7_B2_reading-evolution-of-eye-2011.pdf">"Evolution of the Eye"</A> <SPAN style="font-size:85%;">(PDF)</SPAN>. <I>Scientific American</I>. <B>305</B>: 64–69. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1038%2Fscientificamerican0711-64">10.1038/scientificamerican0711-64</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Scientific+American&rft.atitle=Evolution+of+the+Eye&rft.volume=305&rft.pages=64-69&rft.date=2011&rft_id=info%3Adoi%2F10.1038%2Fscientificamerican0711-64&rft.aulast=Lamb&rft.aufirst=TD&rft_id=http%3A%2F%2Fphysics.okstate.edu%2Faxie%2Fcourses%2F4313%2F2012fall%2FC7_B2_reading-evolution-of-eye-2011.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></LI>
<LI><CITE class="citation book">Land, Michael F.; Nilsson, Dan-Eric (2012). "The origin of vision". <I>Animal Eyes</I> (2 ed.). Oxford: Oxford University Press. pp. 1–22. <A href="/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</A> <A href="/wiki/Special:BookSources/978-0199581146" title="Special:BookSources/978-0199581146">978-0199581146</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=The+origin+of+vision&rft.btitle=Animal+Eyes&rft.place=Oxford&rft.pages=1-22&rft.edition=2&rft.pub=Oxford+University+Press&rft.date=2012&rft.isbn=978-0199581146&rft.aulast=Land&rft.aufirst=Michael+F.&rft.au=Nilsson%2C+Dan-Eric&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></LI>
<LI><A rel="nofollow" class="external text" href="http://www.springerlink.com/content/m3k441k67q3n/?p=debb32f37f44408094bee93d0e48c7b2&pi=1">Journal Evolution: Education and Outreach</A><SUP class="noprint Inline-Template"><SPAN style="white-space: nowrap;">[<I><A href="/wiki/Wikipedia:Link_rot" title="Wikipedia:Link rot"><SPAN title=" Dead link since November 2017">dead link</SPAN></A></I>]</SPAN></SUP> Volume 1, Number 4 / October 2008. Special Issue: The Evolution of Eyes. 26 articles, free access.</LI>
<LI><CITE class="citation book">Ivan R. Schwab (2012). <I>Evolution's Witness: How Eyes Evolved</I>. New York: Oxford University Press. <A href="/wiki/International_Standard_Book_Number" title="International Standard Book Number">ISBN</A> <A href="/wiki/Special:BookSources/9780195369748" title="Special:BookSources/9780195369748">9780195369748</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Evolution%27s+Witness%3A+How+Eyes+Evolved&rft.place=New+York&rft.pub=Oxford+University+Press&rft.date=2012&rft.isbn=9780195369748&rft.au=Ivan+R.+Schwab&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></LI>
<LI><CITE class="citation journal">Hayakawa S, Takaku Y, Hwang JS, Horiguchi T, Suga H, Gehring W, et al. (2015). <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC4348419">"Function and evolutionary origin of unicellular camera-type eye structure"</A>. <I>PLoS ONE</I>. <B>10</B> (3): e0118415. <A href="/wiki/Bibcode" title="Bibcode">Bibcode</A>:<A rel="nofollow" class="external text" href="http://adsabs.harvard.edu/abs/2015PLoSO..1018415H">2015PLoSO..1018415H</A>. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1371%2Fjournal.pone.0118415">10.1371/journal.pone.0118415</A>. <A href="/wiki/PubMed_Central" title="PubMed Central">PMC</A> <SPAN class="plainlinks"><A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pmc/articles/PMC4348419">4348419</A> <IMG alt="Freely accessible" src="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png" title="Freely accessible" width="9" height="14" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/14px-Lock-green.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/18px-Lock-green.svg.png 2x" data-file-width="512" data-file-height="813" /></SPAN>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/25734540">25734540</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=PLoS+ONE&rft.atitle=Function+and+evolutionary+origin+of+unicellular+camera-type+eye+structure&rft.volume=10&rft.issue=3&rft.pages=e0118415&rft.date=2015&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC4348419&rft_id=info%3Apmid%2F25734540&rft_id=info%3Adoi%2F10.1371%2Fjournal.pone.0118415&rft_id=info%3Abibcode%2F2015PLoSO..1018415H&rft.aulast=Hayakawa&rft.aufirst=S&rft.au=Takaku%2C+Y&rft.au=Hwang%2C+JS&rft.au=Horiguchi%2C+T&rft.au=Suga%2C+H&rft.au=Gehring%2C+W&rft_id=%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC4348419&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></LI>
<LI><CITE class="citation journal">Greuet, C (1968). "Organisation ultrastructurale de l'ocelle de deux Peridiniens Warnowiidae, Erythropsis pavillardi Kofoid et Swezy et Warnowia pulchra Schiller". <I>Protistologica</I>. <B>4</B>: 209–230.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Protistologica&rft.atitle=Organisation+ultrastructurale+de+l%E2%80%99ocelle+de+deux+Peridiniens+Warnowiidae%2C+Erythropsis+pavillardi+Kofoid+et+Swezy+et+Warnowia+pulchra+Schiller&rft.volume=4&rft.pages=209-230&rft.date=1968&rft.au=Greuet%2C+C&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></LI>
<LI><CITE class="citation journal">Gregory S. Gavelis, Shiho Hayakawa, Richard A. White III, Takashi Gojobori, Curtis A. Suttle, Patrick J. Keeling, Brian S. Leander (2015). "Eye-like ocelloids are built from different endosymbiotically acquired components". <I>Nature</I>. <B>523</B>: 204–7. <A href="/wiki/Bibcode" title="Bibcode">Bibcode</A>:<A rel="nofollow" class="external text" href="http://adsabs.harvard.edu/abs/2015Natur.523..204G">2015Natur.523..204G</A>. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1038%2Fnature14593">10.1038/nature14593</A>. <A href="/wiki/PubMed_Identifier" class="mw-redirect" title="PubMed Identifier">PMID</A> <A rel="nofollow" class="external text" href="//www.ncbi.nlm.nih.gov/pubmed/26131935">26131935</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Nature&rft.atitle=Eye-like+ocelloids+are+built+from+different+endosymbiotically+acquired+components&rft.volume=523&rft.pages=204-7&rft.date=2015&rft_id=info%3Apmid%2F26131935&rft_id=info%3Adoi%2F10.1038%2Fnature14593&rft_id=info%3Abibcode%2F2015Natur.523..204G&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN><SPAN class="citation-comment" style="display:none; color:#33aa33; margin-left:0.3em">CS1 maint: Uses authors parameter (<A href="/wiki/Category:CS1_maint:_Uses_authors_parameter" title="Category:CS1 maint: Uses authors parameter">link</A>)</SPAN></LI>
<LI><CITE class="citation journal">Oakley, Todd H.; Speiser, Daniel I. (2015). "How Complexity Originates: The Evolution of Animal Eyes". <I>Annual Review of Ecology, Evolution, and Systematics</I>. <B>46</B>: 237–260. <A href="/wiki/Digital_object_identifier" title="Digital object identifier">doi</A>:<A rel="nofollow" class="external text" href="//doi.org/10.1146%2Fannurev-ecolsys-110512-135907">10.1146/annurev-ecolsys-110512-135907</A>.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Annual+Review+of+Ecology%2C+Evolution%2C+and+Systematics&rft.atitle=How+Complexity+Originates%3A+The+Evolution+of+Animal+Eyes&rft.volume=46&rft.pages=237-260&rft.date=2015&rft_id=info%3Adoi%2F10.1146%2Fannurev-ecolsys-110512-135907&rft.aulast=Oakley&rft.aufirst=Todd+H.&rft.au=Speiser%2C+Daniel+I.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></LI>
<LI><CITE class="citation journal">Ed Young; photographs by David Liittschwager (February 2016). <A rel="nofollow" class="external text" href="http://ngm.nationalgeographic.com/2016/02/evolution-of-eyes-text">"Inside the Eye: Nature's Most Exquisite Creation"</A>. <I><A href="/wiki/National_Geographic_(magazine)" class="mw-redirect" title="National Geographic (magazine)">National Geographic</A></I>. <B>229</B> (2): 30–57.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=National+Geographic&rft.atitle=Inside+the+Eye%3A+Nature%E2%80%99s+Most+Exquisite+Creation&rft.volume=229&rft.issue=2&rft.pages=30-57&rft.date=2016-02&rft.au=Ed+Young&rft.au=photographs+by+David+Liittschwager&rft_id=http%3A%2F%2Fngm.nationalgeographic.com%2F2016%2F02%2Fevolution-of-eyes-text&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></LI>
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<H2><SPAN class="mw-headline" id="External_links">External links</SPAN><SPAN class="mw-editsection"><SPAN class="mw-editsection-bracket">[</SPAN><A href="/w/index.php?title=Evolution_of_the_eye&action=edit&section=17" title="Edit section: External links">edit</A><SPAN class="mw-editsection-bracket">]</SPAN></SPAN></H2>
<UL>
<LI><CITE class="citation web"><A rel="nofollow" class="external text" href="https://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html">"Evolution of the Eye"</A>. <I>WGBH Educational Foundation and Clear Blue Sky Productions</I>. PBS. 2001.</CITE><SPAN title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=WGBH+Educational+Foundation+and+Clear+Blue+Sky+Productions&rft.atitle=Evolution+of+the+Eye&rft.date=2001&rft_id=https%3A%2F%2Fwww.pbs.org%2Fwgbh%2Fevolution%2Flibrary%2F01%2F1%2Fl_011_01.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AEvolution+of+the+eye" class="Z3988"><SPAN style="display:none;"> </SPAN></SPAN></LI>
<LI><A rel="nofollow" class="external text" href="https://www.youtube.com/watch?v=fOtP7HEuDYA&eurl=http://www.expelledexposed.com/">Creationism Disproved?</A> Video from the <A href="/wiki/National_Center_for_Science_Education" title="National Center for Science Education">National Center for Science Education</A> on the evolution of the eye</LI>
<LI><A rel="nofollow" class="external text" href="http://www.springerlink.com/content/m3k441k67q3n/"><I>Evolution: Education and Outreach</I> Special Issue: Evolution and Eyes</A> volume 1, number 4, October 2008, pages 351-559. ISSN 1936-6426 (Print) 1936-6434 (Online)</LI>
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<LI><A href="/wiki/Evolution_of_fish" title="Evolution of fish">Fish</A></LI>
<LI><A href="/wiki/Evolution_of_fungi" title="Evolution of fungi">Fungi</A></LI>
<LI><A href="/wiki/Evolution_of_insects" title="Evolution of insects">Insects</A>
<UL>
<LI><A href="/wiki/Evolution_of_butterflies" title="Evolution of butterflies">butterflies</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Evolutionary_history_of_life" title="Evolutionary history of life">Life</A></LI>
<LI><A href="/wiki/Evolution_of_mammals" title="Evolution of mammals">Mammals</A>
<UL>
<LI><A href="/wiki/Cat_gap" title="Cat gap">cats</A></LI>
<LI><A href="/wiki/Evolution_of_canids" class="mw-redirect" title="Evolution of canids">canids</A>
<UL>
<LI><A href="/wiki/Evolution_of_the_wolf" title="Evolution of the wolf">wolves</A></LI>
<LI><A href="/wiki/Origin_of_the_domestic_dog" title="Origin of the domestic dog">dogs</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Evolution_of_hyenas" class="mw-redirect" title="Evolution of hyenas">hyenas</A></LI>
<LI><A href="/wiki/Evolution_of_cetaceans" title="Evolution of cetaceans">dolphins and whales</A></LI>
<LI><A href="/wiki/Evolution_of_the_horse" title="Evolution of the horse">horses</A></LI>
<LI><A href="/wiki/Evolution_of_primates" title="Evolution of primates">primates</A>
<UL>
<LI><A href="/wiki/Human_evolution" title="Human evolution">humans</A></LI>
<LI><A href="/wiki/Evolution_of_lemurs" title="Evolution of lemurs">lemurs</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Evolution_of_sirenians" title="Evolution of sirenians">sea cows</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Evolutionary_history_of_plants" title="Evolutionary history of plants">Plants</A></LI>
<LI><A href="/wiki/Evolution_of_reptiles" title="Evolution of reptiles">Reptiles</A></LI>
<LI><A href="/wiki/Evolution_of_spiders" title="Evolution of spiders">Spiders</A></LI>
<LI><A href="/wiki/Evolution_of_tetrapods" title="Evolution of tetrapods">Tetrapods</A></LI>
<LI><A href="/wiki/Viral_evolution" title="Viral evolution">Viruses</A>
<UL>
<LI><A href="/wiki/Evolution_of_influenza" title="Evolution of influenza">influenza</A></LI>
</UL>
</LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%">Of <A href="/wiki/Organ_(anatomy)" title="Organ (anatomy)">organs</A></TH>
<TD class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Evolution_of_cells" title="Evolution of cells">Cell</A></LI>
<LI><A href="/wiki/Models_of_DNA_evolution" title="Models of DNA evolution">DNA</A></LI>
<LI><A href="/wiki/Evolution_of_flagella" title="Evolution of flagella">Flagella</A></LI>
<LI><A href="/wiki/Eukaryote#Origin_of_eukaryotes" title="Eukaryote">Eukaryotes</A>
<UL>
<LI><A href="/wiki/Symbiogenesis" title="Symbiogenesis">symbiogenesis</A></LI>
<LI><A href="/wiki/Chromosome#Evolution_of_eukaryotic_chromosome" title="Chromosome">chromosome</A></LI>
<LI><A href="/wiki/Endomembrane_system#Evolution" title="Endomembrane system">endomembrane system</A></LI>
<LI><A href="/wiki/Mitochondrion#Origin" title="Mitochondrion">mitochondria</A></LI>
<LI><A href="/wiki/Cell_nucleus#Evolution" title="Cell nucleus">nucleus</A></LI>
<LI><A href="/wiki/Plastid#Origin_of_plastids" title="Plastid">plastids</A></LI>
</UL>
</LI>
<LI>In animals
<UL>
<LI><A class="mw-selflink selflink">eye</A></LI>
<LI><A href="/wiki/Evolution_of_hair" class="mw-redirect" title="Evolution of hair">hair</A></LI>
<LI><A href="/wiki/Evolution_of_mammalian_auditory_ossicles" title="Evolution of mammalian auditory ossicles">auditory ossicle</A></LI>
<LI><A href="/wiki/Evolution_of_nervous_systems" title="Evolution of nervous systems">nervous system</A></LI>
<LI><A href="/wiki/Evolution_of_the_brain" title="Evolution of the brain">brain</A></LI>
</UL>
</LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%">Of <A href="/wiki/Biological_process" title="Biological process">processes</A></TH>
<TD class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Evolution_of_ageing" title="Evolution of ageing">Aging</A>
<UL>
<LI><A href="/wiki/Death#Evolution_of_aging_and_mortality" title="Death">Death</A></LI>
<LI><A href="/wiki/Programmed_cell_death#Evolutionary_origin" title="Programmed cell death">Programmed cell death</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Origin_of_avian_flight" title="Origin of avian flight">Avian flight</A></LI>
<LI><A href="/wiki/Evolution_of_biological_complexity" title="Evolution of biological complexity">Biological complexity</A></LI>
<LI><A href="/wiki/Co-operation_(evolution)" title="Co-operation (evolution)">Cooperation</A></LI>
<LI><A href="/wiki/Evolution_of_color_vision" title="Evolution of color vision">Color vision</A>
<UL>
<LI><A href="/wiki/Evolution_of_color_vision_in_primates" title="Evolution of color vision in primates">in primates</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Evolution_of_emotion" title="Evolution of emotion">Emotion</A></LI>
<LI><A href="/wiki/Empathy#Evolution_of_empathy" title="Empathy">Empathy</A></LI>
<LI><A href="/wiki/Evolutionary_ethics" title="Evolutionary ethics">Ethics</A></LI>
<LI><A href="/wiki/Evolution_of_eusociality" title="Evolution of eusociality">Eusociality</A></LI>
<LI><A href="/wiki/Immune_system#Other_mechanisms_and_evolution" title="Immune system">Immune system</A></LI>
<LI><A href="/wiki/Metabolism#Evolution" title="Metabolism">Metabolism</A></LI>
<LI><A href="/wiki/Monogamy_in_animals" title="Monogamy in animals">Monogamy</A></LI>
<LI><A href="/wiki/Evolution_of_morality" title="Evolution of morality">Morality</A></LI>
<LI><A href="/wiki/Mosaic_evolution" title="Mosaic evolution">Mosaic evolution</A></LI>
<LI><A href="/wiki/Evolution_of_multicellularity" class="mw-redirect" title="Evolution of multicellularity">Multicellularity</A></LI>
<LI><A href="/wiki/Evolution_of_sexual_reproduction" title="Evolution of sexual reproduction">Sexual reproduction</A>
<UL>
<LI><A href="/wiki/Anisogamy#Evolution_of_anisogamy" title="Anisogamy">Gamete differentiation/sexes</A></LI>
<LI><A href="/wiki/Biological_life_cycle" title="Biological life cycle">Life cycles/nuclear phases</A></LI>
<LI><A href="/wiki/Mating_type" title="Mating type">Mating types</A></LI>
<LI><A href="/wiki/Sex-determination_system#Evolution_of_sex-determination_systems" title="Sex-determination system">Sex-determination</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Evolution_of_snake_venom" title="Evolution of snake venom">Snake venom</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Tempo_and_Mode_in_Evolution" title="Tempo and Mode in Evolution">Tempo and modes</A></TH>
<TD class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Phyletic_gradualism" title="Phyletic gradualism">Gradualism</A>/<A href="/wiki/Punctuated_equilibrium" title="Punctuated equilibrium">Punctuated equilibrium</A>/<A href="/wiki/Saltation_(biology)" title="Saltation (biology)">Saltationism</A></LI>
<LI><A href="/wiki/Micromutation" class="mw-redirect" title="Micromutation">Micromutation</A>/<A href="/wiki/Macromutation" class="mw-redirect" title="Macromutation">Macromutation</A></LI>
<LI><A href="/wiki/Uniformitarianism" title="Uniformitarianism">Uniformitarianism</A>/<A href="/wiki/Catastrophism" title="Catastrophism">Catastrophism</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Speciation" title="Speciation">Speciation</A></TH>
<TD class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Allopatric_speciation" title="Allopatric speciation">Allopatric</A></LI>
<LI><A href="/wiki/Anagenesis" title="Anagenesis">Anagenesis</A></LI>
<LI><A href="/wiki/Catagenesis_(biology)" title="Catagenesis (biology)">Catagenesis</A></LI>
<LI><A href="/wiki/Cladogenesis" title="Cladogenesis">Cladogenesis</A></LI>
<LI><A href="/wiki/Cospeciation" title="Cospeciation">Cospeciation</A></LI>
<LI><A href="/wiki/Ecological_speciation" title="Ecological speciation">Ecological</A></LI>
<LI><A href="/wiki/Hybrid_speciation" title="Hybrid speciation">Hybrid</A></LI>
<LI><A href="/wiki/Parapatric_speciation" title="Parapatric speciation">Parapatric</A></LI>
<LI><A href="/wiki/Peripatric_speciation" title="Peripatric speciation">Peripatric</A></LI>
<LI><A href="/wiki/Reinforcement_(speciation)" title="Reinforcement (speciation)">Reinforcement</A></LI>
<LI><A href="/wiki/Sympatric_speciation" title="Sympatric speciation">Sympatric</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/History_of_evolutionary_thought" title="History of evolutionary thought">History</A></TH>
<TD class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Evolutionary_ideas_of_the_Renaissance_and_Enlightenment" title="Evolutionary ideas of the Renaissance and Enlightenment">Renaissance and Enlightenment</A></LI>
<LI><A href="/wiki/Transmutation_of_species" title="Transmutation of species">Transmutation of species</A></LI>
<LI><A href="/wiki/Charles_Darwin" title="Charles Darwin">Charles Darwin</A>
<UL>
<LI><I><A href="/wiki/On_the_Origin_of_Species" title="On the Origin of Species">On the Origin of Species</A></I></LI>
</UL>
</LI>
<LI><A href="/wiki/History_of_paleontology" title="History of paleontology">History of paleontology</A></LI>
<LI><A href="/wiki/Transitional_fossil" title="Transitional fossil">Transitional fossil</A></LI>
<LI><A href="/wiki/Blending_inheritance" title="Blending inheritance">Blending inheritance</A></LI>
<LI><A href="/wiki/Mendelian_inheritance" title="Mendelian inheritance">Mendelian inheritance</A></LI>
<LI><A href="/wiki/The_eclipse_of_Darwinism" title="The eclipse of Darwinism">The eclipse of Darwinism</A></LI>
<LI><A href="/wiki/Modern_synthesis_(20th_century)" title="Modern synthesis (20th century)">Modern synthesis</A></LI>
<LI><A href="/wiki/History_of_molecular_evolution" title="History of molecular evolution">History of molecular evolution</A></LI>
<LI><A href="/wiki/Extended_evolutionary_synthesis" title="Extended evolutionary synthesis">Extended evolutionary synthesis</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%">Philosophy</TH>
<TD class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Darwinism" title="Darwinism">Darwinism</A></LI>
<LI><A href="/wiki/Alternatives_to_evolution_by_natural_selection" title="Alternatives to evolution by natural selection">Alternatives</A>
<UL>
<LI><A href="/wiki/Catastrophism" title="Catastrophism">Catastrophism</A></LI>
<LI><A href="/wiki/Lamarckism" title="Lamarckism">Lamarckism</A></LI>
<LI><A href="/wiki/Orthogenesis" title="Orthogenesis">Orthogenesis</A></LI>
<LI><A href="/wiki/Mutationism" title="Mutationism">Mutationism</A></LI>
<LI><A href="/wiki/Saltationism" class="mw-redirect" title="Saltationism">Saltationism</A></LI>
<LI><A href="/wiki/Structuralism_(biology)" title="Structuralism (biology)">Structuralism</A>
<UL>
<LI><A href="/wiki/Spandrel_(biology)" title="Spandrel (biology)">Spandrel</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Theistic_evolution" title="Theistic evolution">Theistic</A></LI>
<LI><A href="/wiki/Vitalism" title="Vitalism">Vitalism</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Teleology_in_biology" title="Teleology in biology">Teleology in biology</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%">Related</TH>
<TD class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Biogeography" title="Biogeography">Biogeography</A></LI>
<LI><A href="/wiki/Ecological_genetics" title="Ecological genetics">Ecological genetics</A></LI>
<LI><A href="/wiki/Molecular_evolution" title="Molecular evolution">Molecular evolution</A></LI>
<LI><A href="/wiki/Phylogenetics" title="Phylogenetics">Phylogenetics</A>
<UL>
<LI><A href="/wiki/Phylogenetic_tree" title="Phylogenetic tree">Tree</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Polymorphism_(biology)" title="Polymorphism (biology)">Polymorphism</A></LI>
<LI><A href="/wiki/Protocell" title="Protocell">Protocell</A></LI>
<LI><A href="/wiki/Systematics" title="Systematics">Systematics</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TD class="navbox-abovebelow" colspan="2">
<DIV>
<UL>
<LI><IMG alt="Category" src="//upload.wikimedia.org/wikipedia/en/thumb/4/48/Folder_Hexagonal_Icon.svg/16px-Folder_Hexagonal_Icon.svg.png" title="Category" width="16" height="14" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/48/Folder_Hexagonal_Icon.svg/24px-Folder_Hexagonal_Icon.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/4/48/Folder_Hexagonal_Icon.svg/32px-Folder_Hexagonal_Icon.svg.png 2x" data-file-width="36" data-file-height="31" /> <B><A href="/wiki/Category:Evolutionary_biology" title="Category:Evolutionary biology">Category</A></B></LI>
<LI><IMG alt="Commons page" src="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/12px-Commons-logo.svg.png" title="Commons page" width="12" height="16" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/18px-Commons-logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/24px-Commons-logo.svg.png 2x" data-file-width="1024" data-file-height="1376" /> <B><A href="https://commons.wikimedia.org/wiki/Category:Evolutionary_biology" class="extiw" title="commons:Category:Evolutionary biology">Commons</A></B></LI>
<LI><IMG alt="Portal" src="//upload.wikimedia.org/wikipedia/en/thumb/f/fd/Portal-puzzle.svg/16px-Portal-puzzle.svg.png" title="Portal" width="16" height="14" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/fd/Portal-puzzle.svg/24px-Portal-puzzle.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/fd/Portal-puzzle.svg/32px-Portal-puzzle.svg.png 2x" data-file-width="32" data-file-height="28" /> <B><A href="/wiki/Portal:Evolutionary_biology" title="Portal:Evolutionary biology">Portal</A></B></LI>
<LI><IMG alt="WikiProject" src="//upload.wikimedia.org/wikipedia/commons/thumb/3/37/People_icon.svg/16px-People_icon.svg.png" title="WikiProject" width="16" height="16" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/37/People_icon.svg/24px-People_icon.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/37/People_icon.svg/32px-People_icon.svg.png 2x" data-file-width="100" data-file-height="100" /> <B><A href="/wiki/Wikipedia:WikiProject_Evolutionary_biology" title="Wikipedia:WikiProject Evolutionary biology">WikiProject</A></B></LI>
</UL>
</DIV>
</TD>
</TR>
</TBODY></TABLE>
</DIV>
<DIV role="navigation" class="navbox" aria-labelledby="Vision_in_animals" style="padding:3px">
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<DIV id="Vision_in_animals" style="font-size:114%;margin:0 4em">Vision in animals</DIV>
</TH>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Visual_system" title="Visual system">Vision</A></TH>
<TD class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Bird_vision" title="Bird vision">Birds</A></LI>
<LI><A href="/wiki/Cat_senses#Sight" title="Cat senses">Cats</A></LI>
<LI><A href="/wiki/Chameleon_vision" title="Chameleon vision">Chameleons</A></LI>
<LI><A href="/wiki/Dinosaur_vision" title="Dinosaur vision">Dinosaurs</A></LI>
<LI><A href="/wiki/Dog_anatomy#Vision" title="Dog anatomy">Dogs</A></LI>
<LI><A href="/wiki/Vision_in_fishes" title="Vision in fishes">Fishes</A></LI>
<LI><A href="/wiki/Equine_vision" title="Equine vision">Horses</A></LI>
<LI><A href="/wiki/Vision_in_toads" title="Vision in toads">Toads</A></LI>
</UL>
</DIV>
</TD>
<TD class="navbox-image" rowspan="5" style="width:1px;padding:0px 0px 0px 2px">
<DIV><A href="/wiki/File:Astronotus_ocellatus_-_closeup_(aka).jpg" class="image" title="Fish surveying its world"><IMG alt="Fish surveying its world" src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Astronotus_ocellatus_-_closeup_%28aka%29.jpg/140px-Astronotus_ocellatus_-_closeup_%28aka%29.jpg" width="140" height="93" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Astronotus_ocellatus_-_closeup_%28aka%29.jpg/210px-Astronotus_ocellatus_-_closeup_%28aka%29.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2d/Astronotus_ocellatus_-_closeup_%28aka%29.jpg/280px-Astronotus_ocellatus_-_closeup_%28aka%29.jpg 2x" data-file-width="3008" data-file-height="2000" /></A></DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Eye" title="Eye">Eyes</A></TH>
<TD class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Arthropod_eye" title="Arthropod eye">Arthropod eye</A></LI>
<LI><A href="/wiki/Compound_eye" title="Compound eye">Compound eye</A></LI>
<LI><A href="/wiki/Eagle_eye" title="Eagle eye">Eagle eye</A></LI>
<LI><A href="/wiki/Tapetum_lucidum" title="Tapetum lucidum">Eye shine</A></LI>
<LI><A href="/wiki/Simple_eye_in_invertebrates" title="Simple eye in invertebrates">Simple eye in invertebrates</A></LI>
<LI><A href="/wiki/Mammalian_eye" title="Mammalian eye">Mammalian eye</A>
<UL>
<LI><A href="/wiki/Human_eye" title="Human eye">Human eye</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Mollusc_eye" title="Mollusc eye">Mollusc eye</A>
<UL>
<LI><A href="/wiki/Cephalopod_eye" title="Cephalopod eye">Cephalopod eye</A></LI>
<LI><A href="/wiki/Gastropod_eye" class="mw-redirect" title="Gastropod eye">Gastropod eye</A></LI>
</UL>
</LI>
<LI><A href="/wiki/Holochroal_eye" title="Holochroal eye">Holochroal eye</A></LI>
<LI><A href="/wiki/Parietal_eye" title="Parietal eye">Parietal eye</A></LI>
<LI><A href="/wiki/Schizochroal_eye" class="mw-redirect" title="Schizochroal eye">Schizochroal eye</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%"><A href="/wiki/Evolution" title="Evolution">Evolution</A></TH>
<TD class="navbox-list navbox-odd" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A class="mw-selflink selflink">Evolution of the eye</A></LI>
<LI><A href="/wiki/Evolution_of_color_vision" title="Evolution of color vision">Evolution of color vision</A></LI>
<LI><A href="/wiki/Evolution_of_color_vision_in_primates" title="Evolution of color vision in primates">Evolution of color vision in primates</A></LI>
</UL>
</DIV>
</TD>
</TR>
<TR style="display: none;">
<TH scope="row" class="navbox-group" style="width:1%">Coloration</TH>
<TD class="navbox-list navbox-even" style="text-align:left;border-left-width:2px;border-left-style:solid;width:100%;padding:0px">
<DIV style="padding:0em 0.25em">
<UL>
<LI><A href="/wiki/Albinism_in_biology" title="Albinism in biology">Albinism in biology</A></LI>
<LI><A href="/wiki/Animal_coloration" title="Animal coloration">Animal coloration</A></LI>
<LI><A href="/wiki/Aposematism" title="Aposematism">Aposematism</A></LI>
<LI><A href="/wiki/Camouflage" title="Camouflage">Camouflage</A></LI>
<LI><A href="/wiki/Chromatophore" title="Chromatophore">Chromatophore</A></LI>
<LI><A href="/wiki/Counter-illumination" title="Counter-illumination">Counter-illumination</A></LI>
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document_title: Evolution of the eye

token: Evolution

token: of

token: the

token: eye

token: wikipedia

token: Jump

token: to

token: navigation

token: search

token: Major

token: stages

token: in

token: evolution

token: vertebrates

token: The

token: is

token: attractive

token: study

token: because

token: distinctively

token: exemplifies

token: an

token: analogous

token: organ

token: found

token: many

token: animal

token: forms

token: Complex

token: image

token: forming

token: eyes

token: have

token: evolved

token: independently

token: several

token: times

token: evolutionary

token: geneticist

token: Walter

token: Gering

token: holds

token: a

token: different

token: opinion

token: According

token: his

token: theory

token: genes

token: engaged

token: with

token: photoreceptor

token: cells

token: so

token: called

token: Pax

token: appeared

token: probably

token: at

token: once

token: life

token: history

token: very

token: early

token: stage

token: Probably

token: complex

token: kinds

question_text: what is the first step in the evolution of the eye