scientificamerican--2020-09-09--Fighting Back against the Loneliness Epidemic

Adhering to social distancing guidelines , I placed the bag on the doorknob , knocked three times loudly , and quickly stepped back six feet I knocked once again and placed my ear by the door .
The faint sound of footsteps informed me that “ Mr .
Roberts ” ( a pseudonym ) was making his way to the door , hindered by the shuffling gait caused by his Parkinson ’ s disease .
He opened the door and thanked me for the meal , but as usual , did not opt to say goodbye immediately .
Instead , @ @ @ @ @ @ @ me about my plans for the weekend .
As my mask was on , he could not read my lips to accommodate his hearing loss , so my emotive hands and eyes had the job of conveying that the banana bread I had baked for the sixth time this week was not up to par .
Unbeknownst to me at first , my poor attempts to crack jokes about my lack of baking acumen were the only social interaction Mr. Roberts would have until his next Meals on Wheels delivery on Monday .
@ @ @ @ @ @ @ senior centers closing , and nursing homes preventing visitors , the number of older adults experiencing loneliness has skyrocketed .
It is true that the loneliness of older adults like Mr. Roberts has been exacerbated by the COVID-19 crisis ; however , it is important for us to understand that when our own stay-at-home orders are lifted , we will be free .
But what about isolated older adults like Mr. Roberts ?
In our case , while the order comes from government officials concerned for our safety , older adults are prescribed @ @ @ @ @ @ @ mobility and a lack of social support .
Their lack of mobility , transportation and social support does not subside with the pandemic .
There is no vaccine , or “ be-all , end-all ” for social isolation and loneliness in older adults .
In fact , 16.8 percent of older adults are homebound .
Their stay-at-home order is permanent .
But the extent of social isolation among older adults , even before the stay-at-home orders , is not all that has been uncovered by the pandemic .
It has exposed everyone to @ @ @ @ @ @ @ social distancing and a lack of social contact .
As all individuals across all generations have remained at home , many vibrant social connections have been formed—especially ones that emphasize the intricacy of the intergenerational relationship .
Throughout the country , socially distanced young adults and older adults have formed connections because of similar feelings of isolation .
Many senior centers and nursing homes have promoted friendly conversations between students and older adults .
These conversations have formed relationships that will most likely live past the pandemic and stay strong for years to @ @ @ @ @ @ @ interventions are often inexpensive and highly impactful in providing social support for older adults .
The barriers to these interventions are often logistical , such as a lack of technological access for older adults or a lack of organizational help in forming these connections .
Such issues can often be solved with time and attention from members of our community .
Whether we cross the barriers by advocating for the distribution of technological devices to older adults who are homebound , offering community and college-based initiatives to bring these two generations together , @ @ @ @ @ @ @ orders that some older adults are exposed to , the result is a society that is accommodating to a human ’ s need for social support and interaction .
The “ cure ” for the loneliness epidemic that Mr. Roberts and many other older adults are facing is truly community-based .
It is imperative we use whatever privilege we have , whether that is our knowledge of this loneliness epidemic that exists or our access to technology , to help the older adults around us have a voice in our society , rather @ @ @ @ @ @ @ these conversations going beyond the pandemic , not only does Mr. Roberts receive the social support that he deserves , but I also receive the wisdom and advice that Mr. Roberts takes the time to tell me .
I am looking forward to the day that Mr. Roberts and I can speak with each other without my flailing arms having to communicate my emotions or the active fear of infecting each other .
Until then , our conscious efforts to support each other emotionally during this pandemic and this loneliness epidemic is a @ @ @ @ @ @ @ this crisis and beyond .
I wish to note my profound gratitude to Dr. Andrea Wershof Schwartz , not only for her guidance and support in the writing this article , but also her compassionate mentorship in the field of geriatrics and beyond .

Adhering to social distancing guidelines, I placed the bag on the doorknob, knocked three times loudly, and quickly stepped back six feet
Nothing.
I knocked once again and placed my ear by the door. The faint sound of footsteps informed me that “Mr. Roberts” (a pseudonym) was making his way to the door, hindered by the shuffling gait caused by his Parkinson’s disease. He opened the door and thanked me for the meal, but as usual, did not opt to say goodbye immediately. Instead, he lingered at his door and asked me about my plans for the weekend. As my mask was on, he could not read my lips to accommodate his hearing loss, so my emotive hands and eyes had the job of conveying that the banana bread I had baked for the sixth time this week was not up to par. Unbeknownst to me at first, my poor attempts to crack jokes about my lack of baking acumen were the only social interaction Mr. Roberts would have until his next Meals on Wheels delivery on Monday.
Amidst the amalgamation of stay-at-home orders, senior centers closing, and nursing homes preventing visitors, the number of older adults experiencing loneliness has skyrocketed. It is true that the loneliness of older adults like Mr. Roberts has been exacerbated by the COVID-19 crisis; however, it is important for us to understand that when our own stay-at-home orders are lifted, we will be free. But what about isolated older adults like Mr. Roberts? In our case, while the order comes from government officials concerned for our safety, older adults are prescribed to stay at home by their limited mobility and a lack of social support. Their lack of mobility, transportation and social support does not subside with the pandemic. There is no vaccine, or “be-all, end-all” for social isolation and loneliness in older adults. In fact, 16.8 percent of older adults are homebound. Their stay-at-home order is permanent.
But the extent of social isolation among older adults, even before the stay-at-home orders, is not all that has been uncovered by the pandemic. It has exposed everyone to the feelings and frustration that come with social distancing and a lack of social contact. As all individuals across all generations have remained at home, many vibrant social connections have been formed—especially ones that emphasize the intricacy of the intergenerational relationship. Throughout the country, socially distanced young adults and older adults have formed connections because of similar feelings of isolation. Many senior centers and nursing homes have promoted friendly conversations between students and older adults. These conversations have formed relationships that will most likely live past the pandemic and stay strong for years to come.
These grassroots, mutual aid interventions are often inexpensive and highly impactful in providing social support for older adults. The barriers to these interventions are often logistical, such as a lack of technological access for older adults or a lack of organizational help in forming these connections. Such issues can often be solved with time and attention from members of our community. Whether we cross the barriers by advocating for the distribution of technological devices to older adults who are homebound, offering community and college-based initiatives to bring these two generations together, or spreading awareness of the long-lasting stay-at-home orders that some older adults are exposed to, the result is a society that is accommodating to a human’s need for social support and interaction.
The “cure” for the loneliness epidemic that Mr. Roberts and many other older adults are facing is truly community-based. It is imperative we use whatever privilege we have, whether that is our knowledge of this loneliness epidemic that exists or our access to technology, to help the older adults around us have a voice in our society, rather than eliminate it entirely. By keeping these conversations going beyond the pandemic, not only does Mr. Roberts receive the social support that he deserves, but I also receive the wisdom and advice that Mr. Roberts takes the time to tell me.
I am looking forward to the day that Mr. Roberts and I can speak with each other without my flailing arms having to communicate my emotions or the active fear of infecting each other. Until then, our conscious efforts to support each other emotionally during this pandemic and this loneliness epidemic is a powerful connection that will last us through this crisis and beyond.
I wish to note my profound gratitude to Dr. Andrea Wershof Schwartz, not only for her guidance and support in the writing this article, but also her compassionate mentorship in the field of geriatrics and beyond.


scientificamerican--2020-09-09--First U.S. Small Nuclear Reactor Design Is Approved

The U.S. Nuclear Regulatory Commission ( NRC ) has approved the design of a new kind of reactor , known as a small modular reactor ( SMR ) .
The design , from the Portland , Ore.–based company NuScale Power , is intended to speed construction , lower cost and improve safety over traditional nuclear reactors , which are typically many times larger .
Supporters of SMRs have long touted them as a way to help revive the country ’ s nuclear industry and widen the spread of low-carbon electricity .
But some experts have expressed concerns over the potential @ @ @ @ @ @ @ industry would have to address before any such reactors are actually built .
“ This is a significant milestone not only for NuScale , but also for the entire U.S. nuclear sector , ” said NuScale chairman and CEO John Hopkins in a press release .
The NRC ’ s design approval and related final safety evaluation report ( FSER ) do not mean that the firm can begin constructing reactors .
But utility companies can now apply to the NRC to build and operate NuScale ’ s design .
With almost no @ @ @ @ @ @ @ over the past three decades , SMRs could help reinvigorate a flagging industry .
NuScale ’ s SMR , developed with the help of almost $ 300 million from the U.S. Department of Energy , has a generating capacity of 50 megawatts—substantially smaller than standard nuclear reactors , which can range to well more than 1,000 megawatts ( MW ) .
A utility could combine up to 12 SMRs at a single site , producing 600 MW of electricity—enough to power a midsize city .
The NRC says it expects an application for @ @ @ @ @ @ @ SMR in 2022 .
The nuclear industry says SMRs could be built much faster and cheaper than conventional reactors—like products that are rolled off a production line and shipped to various locations rather than custom-built at each site .
A customer could also order and combine various numbers of units , making a wide range of capacity possible .
According to the International Atomic Energy Agency , dozens of SMR designs are under consideration around the world , and several are in “ advanced stages of construction ” in Argentina , China and @ @ @ @ @ @ @ SMRs are the best option for bringing large amounts of emissions-free technology online in the short term to help battle climate change .
Opponents have cited the unresolved issue of disposing nuclear waste , as well as the significant price tag and time involved in building any nuclear plant , compared with renewable energy sources .
NuScale believes it can avoid the dramatic cost overruns and years-long delays that have plagued construction of traditional nuclear power plants in recent decades .
Diane Hughes , the company ’ s vice president of marketing and @ @ @ @ @ @ @ to sell anywhere from 674 to 1,682 reactors between 2023 and 2042 .
The high end of that range would represent more than 80 gigawatts of capacity , which approaches the 98 gigawatts of existing nuclear capacity in the U.S. That power is supplied by just under 100 large reactors ; the existing plants provide approximately 20 percent of the country ’ s electricity .
NuScale has signed memorandums of understanding with companies and utilities in the U.S. , Canada , Jordan , Romania , Ukraine and other countries .
The agreements simply @ @ @ @ @ @ @ deals .
NuScale ’ s first scheduled project is with Utah Associated Municipal Power Systems ( UAMPS ) , a state-based organization that supplies wholesale electricity to small , community-owned utilities in surrounding states .
NuScale plans to deliver its first reactor to the UAMPS project at the Idaho National Laboratory by 2027 ; it is scheduled to be operational by 2029 .
Another 11 reactors will round out the 720-MW project by 2030 .
A portion of the generated power will be sold to the U.S. Department of Energy , with the @ @ @ @ @ @ @ Agreements for some of the power are in place , although a few municipalities have already walked away because of price concerns .
Others have until September 30 to exit the project .
Experts have expressed skepticism about both the safety of the NuScale SMR and its potential costs .
In an online press event on September 2 , M. V. Ramana , a professor and nuclear expert at the University of British Columbia , discussed a report he prepared at the request of Oregon Physicians for Social Responsibility that highlighted significant issues @ @ @ @ @ @ @ I am sorry to say that what lies ahead is risky and expensive , ” Ramana said .
Just in the past five years , he noted , cost estimates from various sources for the UAMPS project have risen from approximately $ 3 billion to more than $ 6 billion .
NuScale ’ s initial goal of having operational reactors by 2016 has been extended by more than a decade , reflecting the sluggish U.S. nuclear industry in general .
Costs to consumers could far exceed those associated with other emissions-free power sources @ @ @ @ @ @ @ added .
And despite the NRC ’ s design approval of the new SMR , some safety features still require adjustment .
“ I don ’ t think future NuScale applicants will benefit from a design certification that has safety gaps in it , ” says Edwin Lyman , director of nuclear power safety at the Union of Concerned Scientists .
He points out that the NRC has issued its final safety report in spite of questions raised both by an expert at the agency and an external advisory board .
In a @ @ @ @ @ @ @ Shanlai Lu discussed a complicated issue known as boron dilution , which could possibly cause “ fuel failure and prompt criticality condition ” —meaning that even if a reactor is shut down , fission reactions could restart and begin a dangerous power increase .
And in another report , the NRC ’ s Advisory Committee on Reactor Safeguards also noted that “ several potentially risk-significant items ” are not yet completed , though it did still recommend that the NRC issue the FSER .
The agency ’ s response to the latter report @ @ @ @ @ @ @ assessed when site-specific licensing applications—the step needed to actually begin building and operating a reactor—are submitted .
“ NuScale and the U.S. Nuclear Regulatory Commission staff examined boron dilution in great detail and reached similar conclusions that the NuScale small modular reactor design is safe and meets all requirements , as is affirmed by the NRC ’ s recent issuance of the FSER , ” NuScale ’ s Hughes says .
Lyman says that in general , the NRC ’ s design certification process should reduce uncertainty for utilities aiming to build nuclear @ @ @ @ @ @ @ safety review .
But he thinks the NuScale approval undermines that advantage .
Whether the gaps in safety will result in further delays to NuScale ’ s time line remains to be seen .
The NRC will undertake another review when the company ’ s 60-MW design is submitted .

The U.S. Nuclear Regulatory Commission (NRC) has approved the design of a new kind of reactor, known as a small modular reactor (SMR). The design, from the Portland, Ore.–based company NuScale Power, is intended to speed construction, lower cost and improve safety over traditional nuclear reactors, which are typically many times larger. Supporters of SMRs have long touted them as a way to help revive the country’s nuclear industry and widen the spread of low-carbon electricity. But some experts have expressed concerns over the potential expense and remaining safety issues that the industry would have to address before any such reactors are actually built.
“This is a significant milestone not only for NuScale, but also for the entire U.S. nuclear sector,” said NuScale chairman and CEO John Hopkins in a press release.
The NRC’s design approval and related final safety evaluation report (FSER) do not mean that the firm can begin constructing reactors. But utility companies can now apply to the NRC to build and operate NuScale’s design. With almost no new nuclear construction completed in the U.S. over the past three decades, SMRs could help reinvigorate a flagging industry.
NuScale’s SMR, developed with the help of almost $300 million from the U.S. Department of Energy, has a generating capacity of 50 megawatts—substantially smaller than standard nuclear reactors, which can range to well more than 1,000 megawatts (MW). A utility could combine up to 12 SMRs at a single site, producing 600 MW of electricity—enough to power a midsize city. The NRC says it expects an application for a 60-MW version of NuScale’s SMR in 2022.
The nuclear industry says SMRs could be built much faster and cheaper than conventional reactors—like products that are rolled off a production line and shipped to various locations rather than custom-built at each site. A customer could also order and combine various numbers of units, making a wide range of capacity possible. According to the International Atomic Energy Agency, dozens of SMR designs are under consideration around the world, and several are in “advanced stages of construction” in Argentina, China and Russia.
Some industry proponents argue that SMRs are the best option for bringing large amounts of emissions-free technology online in the short term to help battle climate change. Opponents have cited the unresolved issue of disposing nuclear waste, as well as the significant price tag and time involved in building any nuclear plant, compared with renewable energy sources.
NuScale believes it can avoid the dramatic cost overruns and years-long delays that have plagued construction of traditional nuclear power plants in recent decades. Diane Hughes, the company’s vice president of marketing and communications, says that the company expects to sell anywhere from 674 to 1,682 reactors between 2023 and 2042. The high end of that range would represent more than 80 gigawatts of capacity, which approaches the 98 gigawatts of existing nuclear capacity in the U.S. That power is supplied by just under 100 large reactors; the existing plants provide approximately 20 percent of the country’s electricity. NuScale has signed memorandums of understanding with companies and utilities in the U.S., Canada, Jordan, Romania, Ukraine and other countries. The agreements simply mean the parties will jointly explore potential deals.
NuScale’s first scheduled project is with Utah Associated Municipal Power Systems (UAMPS), a state-based organization that supplies wholesale electricity to small, community-owned utilities in surrounding states. NuScale plans to deliver its first reactor to the UAMPS project at the Idaho National Laboratory by 2027; it is scheduled to be operational by 2029. Another 11 reactors will round out the 720-MW project by 2030. A portion of the generated power will be sold to the U.S. Department of Energy, with the rest purchased by UAMPS member utilities. Agreements for some of the power are in place, although a few municipalities have already walked away because of price concerns. Others have until September 30 to exit the project.
Experts have expressed skepticism about both the safety of the NuScale SMR and its potential costs. In an online press event on September 2, M. V. Ramana, a professor and nuclear expert at the University of British Columbia, discussed a report he prepared at the request of Oregon Physicians for Social Responsibility that highlighted significant issues associated with the UAMPS project.
“I am sorry to say that what lies ahead is risky and expensive,” Ramana said. Just in the past five years, he noted, cost estimates from various sources for the UAMPS project have risen from approximately $3 billion to more than $6 billion. NuScale’s initial goal of having operational reactors by 2016 has been extended by more than a decade, reflecting the sluggish U.S. nuclear industry in general. Costs to consumers could far exceed those associated with other emissions-free power sources such as solar and wind, Ramana added.
And despite the NRC’s design approval of the new SMR, some safety features still require adjustment. “I don’t think future NuScale applicants will benefit from a design certification that has safety gaps in it,” says Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists. He points out that the NRC has issued its final safety report in spite of questions raised both by an expert at the agency and an external advisory board.
In a July 2020 report, NRC nuclear engineer Shanlai Lu discussed a complicated issue known as boron dilution, which could possibly cause “fuel failure and prompt criticality condition”—meaning that even if a reactor is shut down, fission reactions could restart and begin a dangerous power increase. And in another report, the NRC’s Advisory Committee on Reactor Safeguards also noted that “several potentially risk-significant items” are not yet completed, though it did still recommend that the NRC issue the FSER. The agency’s response to the latter report stated that those items will be further assessed when site-specific licensing applications—the step needed to actually begin building and operating a reactor—are submitted.
“NuScale and the U.S. Nuclear Regulatory Commission staff examined boron dilution in great detail and reached similar conclusions that the NuScale small modular reactor design is safe and meets all requirements, as is affirmed by the NRC’s recent issuance of the FSER,” NuScale’s Hughes says.
Lyman says that in general, the NRC’s design certification process should reduce uncertainty for utilities aiming to build nuclear plants because they can reference a completed safety review. But he thinks the NuScale approval undermines that advantage. Whether the gaps in safety will result in further delays to NuScale’s time line remains to be seen. The NRC will undertake another review when the company’s 60-MW design is submitted.


scientificamerican--2020-09-09--Uber Commits to 100 Percent EVs--Will It Work?

Uber Technologies Inc. yesterday pledged to use only electric vehicles by 2030 in the United States , Canada and Europe , and by 2040 in the rest of the world .
The splashy climate announcement aligned Uber with rival Lyft Inc. , which vowed to reach 100 % EVs by 2030 in late June ( Climatewire , June 22 ) .
It raised questions , however , about the feasibility of both companies ’ commitments , according to experts who study clean transportation .
On a Zoom call with reporters yesterday , Uber CEO Dara Khosrowshahi framed the goal as @ @ @ @ @ @ @ “ During the first lockdown , ” Khosrowshahi said , “ we saw a glimpse of the positive impacts of the record low emissions as a result of less transportation : blue skies replacing smog among city skylines , wildlife returning and pollution levels falling .
Clogged roadways transforming into spaces for walking and cycling.
” He continued : “ But it won ’ t last .
Emission levels are already heading back to pre-COVID highs as recovery from the pandemic continues .
... And at Uber , we ’ ve been thinking @ @ @ @ @ @ @ want to take this moment as an opportunity to do more , to do better , and to do our part to drive a green recovery in our cities.
” In a blog post on Uber ’ s website , Khosrowshahi explained that the commitment includes four prongs .
The first is based on expanding Uber Green , a service that allows riders to choose drivers in hybrid and electric vehicles .
The service will launch in 15 cities in the United States and Canada , including Chicago ; San Francisco ; Los @ @ @ @ @ @ @ Vancouver , British Columbia .
The second prong consists of investing $ 800 million in resources to help hundreds of thousands of drivers transition to EVs by 2025 .
Drivers who switch to fully electric cars will earn an additional $ 1.50 per trip , while drivers who switch to hybrids will earn an extra 50 cents per trip .
In addition , General Motors Co. will offer Uber drivers its employee discount on the new 2020 Chevrolet Bolt and charging accessories , GM said in a news release yesterday .
“ The @ @ @ @ @ @ @ driver on the Uber platform can range from $ 2,500- $ 2,900 below [ Manufacturer ’ s Suggested Retail Price ] depending on how they choose their vehicle , ” GM spokeswoman Maureen Bender wrote in an email to E & E News .
The third prong involves promoting alternatives to cars , including public transit , biking and walking .
A new feature called “ Uber and Transit ” will allow passengers to plan trips that connect to bus and train stations .
David Reich , head of transit at Uber , @ @ @ @ @ @ @ would work by using his hometown of Chicago as an example .
“ We remain fully invested in expanding car-free options globally , ” Reich said while illustrating that a short Uber trip to Wrigley Field—home of the Chicago Cubs—would be half as expensive when paired with transit .
The final prong involves “ being transparent and accountable to the public along the way , ” Khosrowshahi wrote in his blog post .
To that end , the company yesterday published a “ Climate Assessment and Performance Report ” on the carbon intensity @ @ @ @ @ @ @ .
The report showed that ridership grew 36 % over that period , while carbon intensity fell 6 % .
But total emissions still increased dramatically , as a reporter on the call was quick to point out .
The reaction among auto analysts and environmentalists was mixed .
Some praised Uber for reducing its contribution to climate change , while others doubted the company would make good on its promise without increasing incentives for drivers .
Sam Abuelsamid , principal analyst for e-mobility at the consulting firm Guidehouse Insights , fell into @ @ @ @ @ @ @ the average price of a new Chevy Bolt is $ 36,620 .
Even with the employee discount , it would still cost around $ 33,720 .
That ’ s more expensive than popular gas-powered cars like the Nissan Altima ( $ 24,100 ) or the Hyundai Sonata ( $ 23,600 ) .
In addition , Uber drivers are considered independent contractors rather than employees , so they don ’ t receive health insurance or paid time off .
Both Uber and Lyft have vigorously lobbied against state and federal efforts to change that @ @ @ @ @ @ @ employees , it ’ s going to be a challenge for Uber to get them to move over to EVs in the near term , ” Abuelsamid said .
“ I think ultimately , if they want to hit their targets , they ’ re going to have to increase those driver incentives even more than where they are today.
” Gina Coplon-Newfield , director of the Sierra Club ’ s Clean Transportation for All campaign , offered a more positive assessment .
The Sierra Club was one of several environmental groups that @ @ @ @ @ @ @ , along with the World Resources Institute and Transport & Environment .
Coplon-Newfield credited the pressure campaign with nudging the company toward its commitment .
“ Sierra Club supporters over the past year and a half have really been pushing Uber and Lyft to make commitments like electrifying their vehicles and complementing public transit instead of competing with it , ” she said .
Another green group , the Union of Concerned Scientists , turned up the pressure when it published an analysis in February that found ride-hailing services emit nearly 70 % @ @ @ @ @ @ @ replace , including those that involve biking , walking , public transit and private vehicles .
Don Anair , deputy director of the Clean Vehicles Program at the Union of Concerned Scientists and a lead author of the analysis , cheered Uber ’ s commitments while cautioning that they represent “ just one piece of the puzzle.
” The other pieces , he said , are policies and regulations that support the adoption of EVs and the build-out of car charging infrastructure .
One such regulation is taking shape in California , where @ @ @ @ @ @ @ Utilities Commission are drafting the Clean Miles Standard .
It would require ride-hailing companies to develop emissions reduction plans and increase their reliance on EVs .
As California regulators continue drafting the rule over the next few months , Anair said , Uber should “ support the level of stringency of these standards that would be consistent with what they ’ re saying publicly.
” Reprinted from Climatewire with permission from E & E News .
E & E provides daily coverage of essential energy and environmental news at www.eenews.net .

Uber Technologies Inc. yesterday pledged to use only electric vehicles by 2030 in the United States, Canada and Europe, and by 2040 in the rest of the world.
The splashy climate announcement aligned Uber with rival Lyft Inc., which vowed to reach 100% EVs by 2030 in late June (Climatewire, June 22).
It raised questions, however, about the feasibility of both companies’ commitments, according to experts who study clean transportation.
On a Zoom call with reporters yesterday, Uber CEO Dara Khosrowshahi framed the goal as a response to the coronavirus pandemic.
“During the first lockdown,” Khosrowshahi said, “we saw a glimpse of the positive impacts of the record low emissions as a result of less transportation: blue skies replacing smog among city skylines, wildlife returning and pollution levels falling. Clogged roadways transforming into spaces for walking and cycling.”
He continued: “But it won’t last. Emission levels are already heading back to pre-COVID highs as recovery from the pandemic continues. ... And at Uber, we’ve been thinking about what we can do. We want to take this moment as an opportunity to do more, to do better, and to do our part to drive a green recovery in our cities.”
In a blog post on Uber’s website, Khosrowshahi explained that the commitment includes four prongs.
The first is based on expanding Uber Green, a service that allows riders to choose drivers in hybrid and electric vehicles. The service will launch in 15 cities in the United States and Canada, including Chicago; San Francisco; Los Angeles; Seattle; Toronto; and Vancouver, British Columbia.
The second prong consists of investing $800 million in resources to help hundreds of thousands of drivers transition to EVs by 2025. Drivers who switch to fully electric cars will earn an additional $1.50 per trip, while drivers who switch to hybrids will earn an extra 50 cents per trip.
In addition, General Motors Co. will offer Uber drivers its employee discount on the new 2020 Chevrolet Bolt and charging accessories, GM said in a news release yesterday.
“The GM Employee Discount value for the average driver on the Uber platform can range from $2,500-$2,900 below [Manufacturer’s Suggested Retail Price] depending on how they choose their vehicle,” GM spokeswoman Maureen Bender wrote in an email to E&E News.
The third prong involves promoting alternatives to cars, including public transit, biking and walking. A new feature called “Uber and Transit” will allow passengers to plan trips that connect to bus and train stations.
David Reich, head of transit at Uber, demonstrated on Zoom how the new feature would work by using his hometown of Chicago as an example.
“We remain fully invested in expanding car-free options globally,” Reich said while illustrating that a short Uber trip to Wrigley Field—home of the Chicago Cubs—would be half as expensive when paired with transit.
The final prong involves “being transparent and accountable to the public along the way,” Khosrowshahi wrote in his blog post.
To that end, the company yesterday published a “Climate Assessment and Performance Report” on the carbon intensity of its rides from 2017 to 2019. The report showed that ridership grew 36% over that period, while carbon intensity fell 6%.
But total emissions still increased dramatically, as a reporter on the call was quick to point out.
‘One piece of the puzzle’
The reaction among auto analysts and environmentalists was mixed. Some praised Uber for reducing its contribution to climate change, while others doubted the company would make good on its promise without increasing incentives for drivers.
Sam Abuelsamid, principal analyst for e-mobility at the consulting firm Guidehouse Insights, fell into the latter camp.
He noted that the average price of a new Chevy Bolt is $36,620. Even with the employee discount, it would still cost around $33,720. That’s more expensive than popular gas-powered cars like the Nissan Altima ($24,100) or the Hyundai Sonata ($23,600).
In addition, Uber drivers are considered independent contractors rather than employees, so they don’t receive health insurance or paid time off. Both Uber and Lyft have vigorously lobbied against state and federal efforts to change that.
“With the drivers not being employees, it’s going to be a challenge for Uber to get them to move over to EVs in the near term,” Abuelsamid said. “I think ultimately, if they want to hit their targets, they’re going to have to increase those driver incentives even more than where they are today.”
Gina Coplon-Newfield, director of the Sierra Club’s Clean Transportation for All campaign, offered a more positive assessment.
The Sierra Club was one of several environmental groups that met with Uber to advocate for electrification, along with the World Resources Institute and Transport & Environment. Coplon-Newfield credited the pressure campaign with nudging the company toward its commitment.
“Sierra Club supporters over the past year and a half have really been pushing Uber and Lyft to make commitments like electrifying their vehicles and complementing public transit instead of competing with it,” she said.
Another green group, the Union of Concerned Scientists, turned up the pressure when it published an analysis in February that found ride-hailing services emit nearly 70% more climate pollution than the trips they replace, including those that involve biking, walking, public transit and private vehicles.
Don Anair, deputy director of the Clean Vehicles Program at the Union of Concerned Scientists and a lead author of the analysis, cheered Uber’s commitments while cautioning that they represent “just one piece of the puzzle.” The other pieces, he said, are policies and regulations that support the adoption of EVs and the build-out of car charging infrastructure.
One such regulation is taking shape in California, where the state Air Resources Board and Public Utilities Commission are drafting the Clean Miles Standard. It would require ride-hailing companies to develop emissions reduction plans and increase their reliance on EVs.
As California regulators continue drafting the rule over the next few months, Anair said, Uber should “support the level of stringency of these standards that would be consistent with what they’re saying publicly.”
Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.


scientificamerican--2020-09-09--Scientists React to Halt of Leading Coronavirus Vaccine Trial

Enrolment in global trials of a leading coronavirus-vaccine candidate are on hold after a ‘ suspected adverse event ’ in a person who received the vaccine in the United Kingdom .
Scientists say that it ’ s too soon to say what impact this might have on the global push to develop a vaccine , but that the news highlights the importance of waiting for the results of large , properly designed trials to assess safety before approving a vaccine for widespread use .
Researchers at the University of Oxford , UK , in collaboration with the pharmaceutical company AstraZeneca @ @ @ @ @ @ @ is one of nine coronavirus vaccines in the final , ‘ phase III ’ stage of being tested .
Details of the adverse event , including how serious it is and when it happened , have not been reported by Oxford or AstraZeneca .
But the trial ’ s pause comes amid concerns that US drug agencies might face political pressure to approve a vaccine before trials are completed , ahead of the US presidential election in November .
“ The clinical hold shows that there are functioning checks and balances , in @ @ @ @ @ @ @ Marie-Paule Kieny , a vaccine researcher at INSERM , the French national health-research institute in Paris .
“ It might indeed remind everybody—even presidents—that for vaccines , safety is paramount , ” she says .
“ I do hope that the adverse event is unrelated to the vaccine , since Oxford ’ s candidate seems quite promising so far , ” says Florian Krammer , a virologist at the Icahn School of Medicine at Mount Sinai in New York City .
The decision to halt the trial shows that the process to evaluate @ @ @ @ @ @ @ safe and effective therapies make it to the market , he says .
On Tuesday , health-news website STAT reported that the US phase III trial of the coronavirus-vaccine candidate had been paused .
On Wednesday , the University of Oxford confirmed to Nature that enrolment in trials of the vaccine in Brazil , South Africa and the United Kingdom will also be paused .
“ As part of the ongoing randomized , controlled global trials of the Oxford coronavirus vaccine , our standard review process was triggered and we voluntarily paused vaccination @ @ @ @ @ @ @ an independent committee , ” AstraZeneca said in a statement .
“ This is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials , while it is investigated .
We are working to expedite the review of the single event to minimize any potential impact on the trial timeline .
We are committed to the safety of our participants and the highest standards of conduct in our trials , ” the statement notes .
“ If the event is linked definitively , or @ @ @ @ @ @ @ it could be a definitive blow to this particular vaccine candidate .
If unrelated , the hold might be lifted in a matter of weeks , ” says Kieny .
But without more details of the adverse event , including how serious it is and when it happened , it is difficult to assess the impact it will have on the trials and the timeline for the vaccine ’ s approval , say scientists .
It is the second time that administration of the vaccine has been paused in the UK , according @ @ @ @ @ @ @ the study and to information sheets uploaded to a clinical trial registry .
Previously , a participant developed symptoms of transverse myelitis , an inflammation of the spinal cord which is often sparked by viral infections , according to an information sheet given to trial participants dated 12 July .
After a safety review , the trial resumed .
The individual was diagnosed with an “ unrelated neurological illness ” .
AstraZeneca started the trial of its vaccine candidate AZD1222 in the United States last month , with plans to enrol 30,000 adults @ @ @ @ @ @ @ .
Efficacy trials in the United Kingdom , Brazil and South Africa involving a total of around 17,000 people are also under way .
In a double-blind trial , roughly 20,000 of the US trial participants were to be given two doses of the vaccine , while the other 10,000 would receive a placebo .
Such large-scale testing in people is needed before regulators , such as the US Food and Drug Administration , will approve a vaccine for widespread use .
Many countries , including the United States , have pre-ordered millions @ @ @ @ @ @ @ the hope that it will be successful .
By late last month , countries had ordered at least 2.94 billion doses — more than any other coronavirus-vaccine candidate .
More than a third of those doses have been bought by the United Kingdom and other European nations , Japan and the United States .
The US Biomedical Advanced Research and Development Authority has given AstraZeneca more than US $ 1 billion to develop the Oxford vaccine .
Adverse events are not uncommon in clinical trials , and are often unrelated to the treatment @ @ @ @ @ @ @ an infectious-disease researcher at University of Queensland in Brisbane , Australia , who has conducted large clinical trials .
For instance , an adverse event would include a participant being admitted to hospital for any reason , and might automatically trigger the pausing of the trial even if the admission was unrelated to the vaccine .
Studies have protocols that specify what type of events trigger a pause , after which there is a process for investigating whether the event is related to the vaccine , he says .
AstraZeneca study protocols have @ @ @ @ @ @ @ not unusual , but given the stakes involved in the development of a safe , effective vaccine , all of the study ’ s details should be made public , says Paul Komesaroff , a physician and bioethicist at Monash University in Melbourne , Australia .
“ The trials are all publicly supported , the disease is posing the greatest threat to humanity in a hundred years , the drug-development processes are highly politicized , and the outcome will only be a successful one if public trust can be secured and maintained , @ @ @ @ @ @ @ that will now review the AstraZeneca data will probably be working out whether the participant who experienced the adverse event received the vaccine or a placebo , say researchers .
If the person received the vaccine , the investigators then have to try to work out whether it caused the adverse event .
“ That can be tough to sleuth out , ” says Jonathan Kimmelman , a bioethicist who studies clinical trials at McGill University in Montreal , Canada .
If the event is significant and found to be related to the @ @ @ @ @ @ @ impact on the study , says Griffin .
“ But I think it is too soon to assume that that is the case , ” he says .
The first priority is making sure that the volunteer is safe and getting the best medical care , he says .
“ I have every confidence that this group will very quickly assess this adverse event and make the results of that investigation known , ” says Griffin .
Researchers have been especially worried that COVID-19 vaccines could cause an ‘ enhanced disease ’ when @ @ @ @ @ @ @ to the virus subsequently .
Animal studies and early-phase human trials of COVID-19 vaccines , including the Oxford/AstraZeneca candidate , have so far reported no signs of enhanced disease .
The Oxford vaccine is a viral-vector vaccine that harnesses a cold-causing ‘ adenovirus ’ isolated from chimpanzees .
The chimpanzee adenovirus has been modified such that it can no longer replicate in cells , and it expresses the ‘ spike ’ protein that the coronavirus uses to infect human cells .
Dozens of groups say they are working on viral-vector vaccines for coronavirus @ @ @ @ @ @ @ drug maker Johnson & Johnson , and another co-developed by the Chinese military and CanSino Biologics , based in Tianjin , China .
This article is reproduced with permission and was first published on September 9 2020 .

Enrolment in global trials of a leading coronavirus-vaccine candidate are on hold after a ‘suspected adverse event’ in a person who received the vaccine in the United Kingdom. Scientists say that it’s too soon to say what impact this might have on the global push to develop a vaccine, but that the news highlights the importance of waiting for the results of large, properly designed trials to assess safety before approving a vaccine for widespread use.
Researchers at the University of Oxford, UK, in collaboration with the pharmaceutical company AstraZeneca, are developing the vaccine, which is one of nine coronavirus vaccines in the final, ‘phase III’ stage of being tested.
Details of the adverse event, including how serious it is and when it happened, have not been reported by Oxford or AstraZeneca. But the trial’s pause comes amid concerns that US drug agencies might face political pressure to approve a vaccine before trials are completed, ahead of the US presidential election in November.
“The clinical hold shows that there are functioning checks and balances, in spite of political pressure,” says Marie-Paule Kieny, a vaccine researcher at INSERM, the French national health-research institute in Paris. “It might indeed remind everybody—even presidents—that for vaccines, safety is paramount,” she says.
“I do hope that the adverse event is unrelated to the vaccine, since Oxford’s candidate seems quite promising so far,” says Florian Krammer, a virologist at the Icahn School of Medicine at Mount Sinai in New York City. The decision to halt the trial shows that the process to evaluate vaccines works, and ensures that only safe and effective therapies make it to the market, he says.
On Tuesday, health-news website STAT reported that the US phase III trial of the coronavirus-vaccine candidate had been paused. On Wednesday, the University of Oxford confirmed to Nature that enrolment in trials of the vaccine in Brazil, South Africa and the United Kingdom will also be paused.
“As part of the ongoing randomized, controlled global trials of the Oxford coronavirus vaccine, our standard review process was triggered and we voluntarily paused vaccination to allow review of safety data by an independent committee,” AstraZeneca said in a statement.
“This is a routine action which has to happen whenever there is a potentially unexplained illness in one of the trials, while it is investigated. We are working to expedite the review of the single event to minimize any potential impact on the trial timeline. We are committed to the safety of our participants and the highest standards of conduct in our trials,” the statement notes.
“If the event is linked definitively, or even probably, to the vaccine, it could be a definitive blow to this particular vaccine candidate. If unrelated, the hold might be lifted in a matter of weeks,” says Kieny.
But without more details of the adverse event, including how serious it is and when it happened, it is difficult to assess the impact it will have on the trials and the timeline for the vaccine’s approval, say scientists.
It is the second time that administration of the vaccine has been paused in the UK, according to two people who took part in the study and to information sheets uploaded to a clinical trial registry. Previously, a participant developed symptoms of transverse myelitis, an inflammation of the spinal cord which is often sparked by viral infections, according to an information sheet given to trial participants dated 12 July. After a safety review, the trial resumed. The individual was diagnosed with an “unrelated neurological illness”.
Cross-country trial
AstraZeneca started the trial of its vaccine candidate AZD1222 in the United States last month, with plans to enrol 30,000 adults at about 80 sites across the country. Efficacy trials in the United Kingdom, Brazil and South Africa involving a total of around 17,000 people are also under way. In a double-blind trial, roughly 20,000 of the US trial participants were to be given two doses of the vaccine, while the other 10,000 would receive a placebo. Such large-scale testing in people is needed before regulators, such as the US Food and Drug Administration, will approve a vaccine for widespread use.
Many countries, including the United States, have pre-ordered millions of doses of the Oxford vaccine in the hope that it will be successful. By late last month, countries had ordered at least 2.94 billion doses — more than any other coronavirus-vaccine candidate. More than a third of those doses have been bought by the United Kingdom and other European nations, Japan and the United States. The US Biomedical Advanced Research and Development Authority has given AstraZeneca more than US$1 billion to develop the Oxford vaccine.
Adverse events are not uncommon in clinical trials, and are often unrelated to the treatment being tested, says Paul Griffin, an infectious-disease researcher at University of Queensland in Brisbane, Australia, who has conducted large clinical trials. For instance, an adverse event would include a participant being admitted to hospital for any reason, and might automatically trigger the pausing of the trial even if the admission was unrelated to the vaccine. Studies have protocols that specify what type of events trigger a pause, after which there is a process for investigating whether the event is related to the vaccine, he says. AstraZeneca study protocols have not been made public.
That is not unusual, but given the stakes involved in the development of a safe, effective vaccine, all of the study’s details should be made public, says Paul Komesaroff, a physician and bioethicist at Monash University in Melbourne, Australia. “The trials are all publicly supported, the disease is posing the greatest threat to humanity in a hundred years, the drug-development processes are highly politicized, and the outcome will only be a successful one if public trust can be secured and maintained,” he says.
What next?
The independent committee that will now review the AstraZeneca data will probably be working out whether the participant who experienced the adverse event received the vaccine or a placebo, say researchers. If the person received the vaccine, the investigators then have to try to work out whether it caused the adverse event. “That can be tough to sleuth out,” says Jonathan Kimmelman, a bioethicist who studies clinical trials at McGill University in Montreal, Canada.
If the event is significant and found to be related to the vaccine, that might have a significant impact on the study, says Griffin. “But I think it is too soon to assume that that is the case,” he says. The first priority is making sure that the volunteer is safe and getting the best medical care, he says.
“I have every confidence that this group will very quickly assess this adverse event and make the results of that investigation known,” says Griffin.
Researchers have been especially worried that COVID-19 vaccines could cause an ‘enhanced disease’ when people who receive the vaccine are exposed to the virus subsequently. Animal studies and early-phase human trials of COVID-19 vaccines, including the Oxford/AstraZeneca candidate, have so far reported no signs of enhanced disease.
The Oxford vaccine is a viral-vector vaccine that harnesses a cold-causing ‘adenovirus’ isolated from chimpanzees. The chimpanzee adenovirus has been modified such that it can no longer replicate in cells, and it expresses the ‘spike’ protein that the coronavirus uses to infect human cells. Dozens of groups say they are working on viral-vector vaccines for coronavirus, including a candidate developed by US drug maker Johnson & Johnson, and another co-developed by the Chinese military and CanSino Biologics, based in Tianjin, China.
This article is reproduced with permission and was first published on September 9 2020.


scientificamerican--2020-09-09--How Scientists Discovered the Staggering Complexity of Human Evolution

In 1859 , 14 years after the founding of this magazine , Charles Darwin published the most important scientific book ever written .
On the Origin of Species revolutionized society 's understanding of the natural world .
Challenging Victorian dogma , Darwin argued that species were not immutable , each one specially created by God .
Rather life on earth , in all its dazzling variety , had evolved through descent from a common ancestor with modification by means of natural selection .
But for all of Darwin 's brilliant insights into the origins of ants and armadillos , bats @ @ @ @ @ @ @ neglected in the great book : his own .
Of Homo sapiens , Darwin made only a passing mention on the third-to-last page of the tome , noting coyly that “ light will be thrown on the origin of man and his history.
” That 's it .
That is all he wrote about the dawning of the single most consequential species on the planet .
It was not because Darwin thought humans were somehow exempt from evolution .
Twelve years later he published a book devoted to that very subject , The @ @ @ @ @ @ @ he explained that discussing humans in his earlier treatise would have served only to further prejudice readers against his radical idea .
Yet even in this later work , he had little to say about human origins per se , instead focusing on making the case from comparative anatomy , embryology and behavior that , like all species , humans had evolved .
The problem was that there was hardly any fossil record of humans at that time to provide evidence of earlier stages of human existence .
Back then , “ the @ @ @ @ @ @ @ could reason , ” says paleoanthropologist Bernard Wood of George Washington University .
To his credit , Darwin made astute observations about our kind and predictions about our ancient past based on the information that was available to him .
He argued that all living humans belong to one species and that its “ races ” all descended from a single ancestral stock .
And pointing to the anatomical similarities between humans and African apes , he concluded that chimpanzees and gorillas were the closest living relatives of humans .
Given that relationship @ @ @ @ @ @ @ probably lived in Africa .
Since then , Wood says , “ the evidence has come in.
” In the past century and a half , science has confirmed Darwin 's prediction and pieced together a detailed account of our origins .
Paleoanthropologists have recovered fossil hominins ( the group that comprises H. sapiens and its extinct relatives ) spanning the past seven million years .
This extraordinary record shows that hominins indeed got their start in Africa , where they evolved from quadrupedal apes into the upright-walking , nimble-fingered , large-brained creatures @ @ @ @ @ @ @ record of hominin creations , which encompasses roughly half that time , charts their cultural evolution—from early experiments with simple stone tools to the invention of symbols , songs and stories—and maps our ancestors ' spread across the globe .
The fossils and artifacts demonstrate that for most of the period over which our lineage has been evolving , multiple hominin species walked the earth .
Studies of modern and ancient DNA have generated startling insights into what happened when they encountered one another .
The human saga , we now understand , @ @ @ @ @ @ @ yore envisioned .
The tidy tropes of our prehistory have collapsed under the weight of evidence : there is no single missing link that bridges apes and humankind , no drumbeat march of progress toward a predestined goal .
Our story is complicated , messy and random .
Yet it still can be accommodated under Darwin 's theory of evolution and in fact further validates that framework .
This is not to say scientists have it all figured out .
Many questions remain .
But whereas the origin of humans was once an @ @ @ @ @ @ @ , it is now among the best-documented examples of evolution 's transformative power .
We humans are strange creatures .
We walk upright on two legs and possess supersized brains , we invent tools to meet our every need and express ourselves using symbols , and we have conquered every corner of the planet .
For centuries scientists have sought to explain how we came to be , our place in the natural world .
This quest was often distorted by racist ideologies .
Consider the era leading up to the birth of @ @ @ @ @ @ @ 1830s , while a young Darwin was making his momentous voyage onboard the Beagle , a movement was underway to promote the idea that the various modern human groups around the globe—races—had separate origins .
To build the case for polygenism , as the theory is known , scientists such as Samuel Morton in Philadelphia collected skulls from people across the world and measured their sizes and shapes , falsely believing those attributes to be proxies for intelligence .
When they ranked the specimens from superior to inferior , Europeans would conveniently come @ @ @ @ @ @ @ bottom .
“ There was a desire to provide scientific justification for political and power structures , ” says anthropological geneticist Jennifer Raff of the University of Kansas .
“ It was science in the service of slavery and colonialism.
” Although Darwin 's work came down firmly on the side of monogenism—the idea that all humans share a common ancestor—it was nonetheless co-opted to support notions about racial superiority .
Social Darwinism , for one , misapplied Darwin 's ideas about the struggle for existence in natural selection to human society , @ @ @ @ @ @ @ and oppression .
Darwin himself did not subscribe to such views .
In fact , his opposition to slavery may have been a driving force in his research agenda , according to his biographers Adrian Desmond and James Moore .
By the time Darwin published The Descent of Man , in 1871 , the idea that humans had evolved from a common ancestor with apes was already gaining traction in the scientific community thanks to books published in the 1860s by English biologist Thomas Henry Huxley and Scottish geologist Charles Lyell .
Still @ @ @ @ @ @ @ claim was scant .
The only hominin fossils known to science were a handful of remains a few tens of thousands of years old that had been recovered from sites in Europe .
Some were H. sapiens ; others would eventually be recognized as a separate but very closely related species , Homo neanderthalensis .
The implication was that fossils of more apelike human ancestors were out there somewhere in the world , awaiting discovery .
But the suggestion by Darwin , like Huxley before him , that those ancestors would be found @ @ @ @ @ @ @ who saw Asia as a more civilized birthplace for humankind and emphasized similarities between humans and Asia 's gibbons .
Perhaps it should come as no surprise , then , that when the first hominin fossil significantly older and more primitive than those from Europe turned up , it came not from Africa but from Asia .
In 1891 Dutch anatomist Eugène Dubois discovered remains on the Indonesian island of Java that he thought belonged to the long-sought missing link between apes and humans .
The find , which he named Pithecanthropus erectus @ @ @ @ @ @ @ in Asia .
( We now know that Dubois 's fossil was between 700,000 and one million years old and belonged to a hominin that was much more humanlike than apelike , Homo erectus . )
Two decades later the search turned to Europe .
In 1912 amateur archaeologist Charles Dawson reported that he had found a skull with a humanlike cranium and an apelike jaw in an ancient gravel pit near the site of Piltdown in East Sussex , England .
Piltdown Man , as the specimen was nicknamed , was a @ @ @ @ @ @ @ it was exposed in 1953 as a fraudulent pairing of a modern human skull with an orangutan 's lower jaw .
Piltdown so seduced scholars with the prospect of making Europe the seat of human origins that they all but ignored an actual ancient hominin that turned up in Africa , one even older and more apelike than the one Dubois discovered .
In 1925 , 43 years after Darwin 's death , anatomist Raymond Dart published a paper describing a fossil from Taung , South Africa , with an apelike braincase and @ @ @ @ @ @ @ youngster 's skull now known to be around 2.8 million years old—Australopithecus africanus , “ the southern ape from Africa.
” But it would take nearly 20 years for the scientific establishment to accept Dart 's argument that the so-called Taung Child was of immense significance : the fossil linked humans to African apes .
Evidence of humanity 's African origins has accumulated ever since .
Every hominin trace older than 2.1 million years—and there are now quite a few of them—has come from that continent .
Even as fossil discoveries proved Darwin @ @ @ @ @ @ @ the pattern of our emergence remained elusive .
Darwin himself depicted evolution as a branching process in which ancestral species divide into two or more descendant species .
But a long-standing tradition of organizing nature hierarchically—one that dates back to Plato and Aristotle 's Great Chain of Being—held sway , giving rise to the notion that our evolution unfolded in linear fashion from simple to complex , primitive to modern .
Popular imagery reflected and reinforced this idea , from a caricature in Punch 's Almanack for 1882 showing a progression from earthworm @ @ @ @ @ @ @ illustration that appeared in the 1965 Time-Life book Early Man and became known as the March of Progress .
From the rich assortment of fossils and artifacts recovered from around the world in the past century , however , paleoanthropologists can now reconstruct something of the timing and pattern of human evolution .
The finds clearly show that this single-file scheme is no longer tenable .
Evolution does not march steadily toward predetermined goals .
And many hominin specimens belong not in our direct line of ancestry but on side branches of humankind—evolutionary @ @ @ @ @ @ @ the outset , our defining traits evolved not in lockstep but piecemeal .
Take our mode of locomotion , for example .
H. sapiens is what anthropologists call an obligate biped—our bodies are built for walking on two legs on the ground .
We can climb trees if we need to , but we have lost the physical adaptations that other primates have to arboreal life .
Fragmentary fossils of the oldest known hominins—Sahelanthropus tchadensis from Chad , Orrorin tugenensis from Kenya and Ardipithecus kadabba from Ethiopia—show that our earliest ancestors emerged by @ @ @ @ @ @ @ ago .
Although they are apelike in many respects .
all of them exhibit characteristics associated with walking on two legs instead of four .
In Sahelanthropus , for example , the hole in the base of the skull through which the spinal cord passes has a forward position suggestive of an upright posture .
A bipedal gait may thus have been one of the very first traits that distinguished hominins from ancestral apes .
Yet our forebears appear to have retained traits needed for arboreal locomotion for millions of years after they @ @ @ @ @ @ @ two legs .
Australopithecus afarensis , which lived in eastern Africa from 3.85 million to 2.95 million years ago and is famously represented by the skeleton known as Lucy , discovered in 1974 , was a capable biped .
But it had long , strong arms and curved fingers—features associated with tree climbing .
It would be another million years before modern limb proportions evolved and committed hominins to life on the ground , starting with early H. erectus in Africa ( sometimes called Homo ergaster ) .
The brain evolved on quite @ @ @ @ @ @ @ of human evolution , brain size has more than tripled .
A comparison of the braincase of A. afarensis with that of the much older Sahelanthropus , however , shows that hardly any of that growth occurred in the first few million years of human evolution .
In fact , most of the expansion took place in the past two million years , perhaps enabled by a feedback loop in which advances in technology—stone tools and the like—gave hominins access to more nutritious foods such as meat , which could fuel a larger @ @ @ @ @ @ @ which in turn could dream up even better technology , and so on .
Shifts in the shape and structure of the brain accompanied these gains , with more real estate allocated to regions involved in language and long-range planning , among other advanced cognitive functions .
This mosaic pattern of hominin evolution in which different body parts evolved at different rates produced some surprising creatures .
For instance , Australopithecus sediba from South Africa , dated to 1.98 million years ago , had a humanlike hand attached to an apelike arm , @ @ @ @ @ @ @ brain , and an advanced ankle bone connected to a primitive heel bone .
Sometimes evolution even doubled back on itself .
When one examines a hominin fossil , it can be difficult to discern whether the species retained a primitive trait such as small brain size from an earlier ancestor or whether it lost the characteristic and then re-evolved it .
But the strange case of Homo floresiensis may well be an example of the latter .
This member of the human family lived on the island of Flores in Indonesia as @ @ @ @ @ @ @ in many ways like some of the founding members of our genus who lived more than two million years earlier .
Not only did H. floresiensis have a small body , but it also possessed a remarkably tiny brain for Homo , about the size of a chimp 's .
Scientists ' best guess is that this species descended from a brawnier , brainer Homo species that got marooned on Flores and evolved its diminutive size as an adaptation to the limited food resources available on its island home .
In so doing @ @ @ @ @ @ @ what researchers once considered a defining trend of Homo 's evolution : the inexorable expansion of the brain .
Yet despite its small brain , H. floresiensis still managed to make stone tools , hunt animals for food and cook over fires .
Adding to the complexity of our story , it is now clear that for most of the time over which humans have been evolving , multiple hominin species walked the earth .
Between 3.6 million and 3.3 million years ago , for example , at least four varieties of hominins @ @ @ @ @ @ @ of the Cleveland Museum of Natural History and his team have recovered remains of two of them , A. afarensis and Australopithecus deyiremeda , as well as a possible third creature known only from a distinctive fossil foot , in a single area called Woranso-Mille in Ethiopia 's Afar region .
How they managed to share the landscape is a subject of current investigation .
“ Competing species could co-exist if there were plenty of resources or if they were exploiting different parts of the ecosystem , ” Haile-Selassie says .
Later , @ @ @ @ @ @ @ years ago , representatives of our genus , Homo—large-brained tool users with dainty jaws and teeth—shared the grasslands of southern and eastern Africa with a radically different branch of humanity .
Members of the genus Paranthropus , these hominins had massive teeth and jaws , flaring cheek bones and crests atop their heads that anchored powerful chewing muscles .
Here the co-existence is somewhat better understood : whereas Homo seems to have evolved to exploit a wide variety of plants and animals for food , Paranthropus specialized in processing tough , fibrous plant @ @ @ @ @ @ @ kinds of humans , too .
When our species was evolving in Africa 300,000 years ago , several other kinds of hominins also roamed the planet .
Some , such as the stocky Neandertals in Eurasia , were very close relatives .
Others , including Homo naledi in South Africa and H. erectus in Indonesia , belonged to lineages that diverged from ours in the deep past .
Even as recently as 50,000 years ago , hominin diversity was the rule , with the Neandertals , the mysterious Denisovans from Asia , tiny @ @ @ @ @ @ @ discovered Homo luzonensis from the Philippines—all at large .
Such discoveries make for a much more interesting picture of human evolution than the linear account that has dominated our view of life .
But they raise a nagging question : How did H. sapiens end up being the sole surviving twig on what was once a luxuriant evolutionary bush ?
Here are the facts of the case .
We know from fossils found at the site of Jebel Irhoud in Morocco that our species originated in Africa by at least 315,000 years ago @ @ @ @ @ @ @ began making forays out of Africa , and by 40,000 years ago it had established itself throughout Eurasia .
Some of the places H. sapiens colonized were occupied by other hominin species .
Eventually the other folks all disappeared .
By around 30,000 to 15,000 years ago , with the end of the Neandertals in Europe and the Denisovans in Asia , H. sapiens was alone in the world .
Researchers have often attributed the success of our species to superior cognition .
Although the Neandertals actually had slightly larger brains than ours @ @ @ @ @ @ @ that only H. sapiens crafted specialized tools and used symbols , suggesting a capacity for language .
Perhaps , the thinking went , H. sapiens won out by virtue of sharper foresight , better technology , more flexible foraging strategies and bigger social networks for support against hard times .
Alternatively , some investigators have proposed , maybe H. sapiens waged war on its rivals , exterminating them directly .
But recent discoveries have challenged these scenarios .
Neandertal technology , archaeologists have learned , was far more varied and sophisticated than previously @ @ @ @ @ @ @ jewelry and art , crafting pendants from shells and animal teeth and painting abstract symbols on cave walls .
Moreover , they may not have been our only enlightened kin : a 500,000-year-old engraved shell from Java suggests that H. erectus also possessed symbolic thought .
If archaic hominins had many of the same mental faculties as H. sapiens , why did the latter prevail ?
The conditions under which H. sapiens got its start may have played a role .
Fossil and archaeological data suggest that our species mostly stayed in Africa @ @ @ @ @ @ @ years of its existence .
There , some experts argue , it evolved as a population of interconnected subgroups spread across the continent that split up and reunited again and again over millennia , allowing for periods of evolution in isolation followed by opportunities for interbreeding and cultural exchange .
This evolutionary upbringing may have honed H. sapiens into an especially adaptable hominin .
But that is not the whole story , as we now know from genetics .
Analyses of DNA have revolutionized the study of human evolution .
Comparing the human @ @ @ @ @ @ @ great apes has shown conclusively that we are most closely related to chimpanzees and bonobos , sharing nearly 99 percent of their DNA .
And large-scale studies of DNA from modern-day human populations across the globe have illuminated the origins of modern human variation , overturning the centuries-old notion that races are biologically discrete groups with separate origins .
“ There have never been pure populations or races , ” Raff says .
Modern human variation is continuous , and most variation actually exists within populations rather than between them—the product of our @ @ @ @ @ @ @ in Africa with populations that mixed continuously as they migrated around the world .
More recently , studies of ancient DNA have cast new light on the world of early H. sapiens as it was when other hominin species were still running around .
In the late 1990s geneticists began recovering small amounts of DNA from Neandertal and early H. sapiens fossils .
Eventually they succeeded in getting entire genomes not only from Neandertals and early H. sapiens but also from Denisovans , who are known from just a few fragmentary fossils from @ @ @ @ @ @ @ ancient genomes with modern ones , researchers have found evidence that our own species interbred with these other species .
People today carry DNA from Neandertals and Denisovans as a result of these long-ago encounters .
Other studies have found evidence of interbreeding between H. sapiens and unknown extinct hominins from Africa and Asia for whom we have no fossils but whose distinctive DNA persists .
Mating with other human species may have aided H. sapiens ' success .
Studies of organisms ranging from finches to oak trees have shown that hybridization with @ @ @ @ @ @ @ in novel environments by giving them useful genes .
Although scientists have yet to figure out the functions of most of the genes people today carry from extinct hominins , they have pinpointed a few , and the results are intriguing .
For instance , Neandertals gave H. sapiens immunity genes that may have helped our species fend off novel pathogens it encountered in Eurasia , and Denisovans contributed a gene that helped people adapt to high altitudes .
H. sapiens may be the last hominin standing , but it got a leg @ @ @ @ @ @ @ have many more pieces of the human-origins puzzle than they once did , but the puzzle is now vastly bigger than it was previously understood to be .
Many gaps remain , and some may never close .
Take the question of why we evolved such massive brains .
At around 1,400 grams , the modern human brain is considerably larger than expected for a primate of our body size .
“ The singularity is why it 's interesting—and why it 's impossible to answer scientifically , ” Wood observes .
Some experts @ @ @ @ @ @ @ they adapted to climate fluctuations between wet and dry conditions , among other explanations .
But the problem with trying to answer “ why ” questions about the evolution of our unique traits , Wood says , is that there is no way to evaluate the proposed explanations empirically .
“ There is n't a counterfactual .
We ca n't go back to three million years ago and not change the climate.
” Other mysteries may yield to further investigation , however .
For example , we do not yet know what the @ @ @ @ @ @ @ Pan genus that includes chimps and bonobos looked like .
Genomic and fossil data suggest that the two lineages diverged between eight million and 10 million years ago—up to three million years before the oldest known hominin walked the earth—which means that paleoanthropologists may be missing a substantial chunk of our prehistory .
And they have hardly any fossils at all of Pan , which has been evolving along its own path just as long as we have .
Insights may come from a project currently underway in central Mozambique , where Susana @ @ @ @ @ @ @ of Oxford and their colleagues are hunting for fossil primates , including hominins , in sediments older than the ones that yielded Sahelanthropus , Orrorin and Ardipithecus .
Later stages of the human story are riddled with unknowns , too .
If H. sapiens was interbreeding with the other hominin species it encountered , as we now know it was , were these groups also exchanging culture ?
Might H. sapiens have introduced Neandertals to novel hunting technology and artistic traditions—or vice versa ?
New techniques for retrieving ancient DNA and proteins from @ @ @ @ @ @ @ are helping researchers determine which hominin species were active and when at key archaeological sites .
One wonders where the next 175 years will take us in the quest to understand who we are and where we come from .
We may have found our place in nature , located our twig on the shrub , but we are still searching for ourselves .
We 're only human , after all .

In 1859, 14 years after the founding of this magazine, Charles Darwin published the most important scientific book ever written. On the Origin of Species revolutionized society’s understanding of the natural world. Challenging Victorian dogma, Darwin argued that species were not immutable, each one specially created by God. Rather life on Earth, in all its dazzling variety, had evolved through descent from a common ancestor with modification by means of natural selection. But for all of Darwin’s brilliant insights into the origins of ants and armadillos, bats and barnacles, one species is conspicuously neglected in the great book: his own. Of Homo sapiens, Darwin made only a passing mention on the third-to-last page of the tome, noting coyly that “light will be thrown on the origin of man and his history.” That’s it. That is all he wrote about the dawning of the single most consequential species on the planet.
It was not because Darwin thought humans were somehow exempt from evolution. Twelve years later he published a book devoted to that very subject, The Descent of Man. In it, he explained that discussing humans in his earlier treatise would have served only to further prejudice readers against his radical idea. Yet even in this later work, he had little to say about human origins per se, instead focusing on making the case from comparative anatomy, embryology and behavior that, like all species, humans had evolved. The problem was that there was hardly any fossil record of humans at that time to provide evidence of earlier stages of human existence. Back then, “the only thing you knew was what you could reason,” says paleoanthropologist Bernard Wood of the George Washington University.
To his credit, Darwin made astute observations about our kind and predictions about our ancient past based on the information that was available to him. He argued that all living humans belong to one species and that its “races” all descended from a single ancestral stock. And pointing to the anatomical similarities between humans and African apes, he concluded that chimpanzees and gorillas were the closest living relatives of humans. Given that relationship, he figured, early human ancestors probably lived in Africa.
Since then, Wood says, “the evidence has come in.” In the past century and a half, science has confirmed Darwin’s prediction and pieced together a detailed account of our origins. Paleoanthropologists have recovered fossil hominins (the group that comprises H. sapiens and its extinct relatives) spanning the past seven million years. This extraordinary record shows that hominins indeed got their start in Africa, where they evolved from quadrupedal apes into the upright-walking, nimble-fingered, large-brained creatures we are today.
And the archaeological record of hominin creations, which encompasses roughly half that time, charts their cultural evolution—from early experiments with simple stone tools to the invention of symbols, songs and stories—and maps our ancestors’ spread across the globe. The fossils and artifacts demonstrate that for most of the period over which our lineage has been evolving, multiple hominin species walked the earth. Studies of modern and ancient DNA have generated startling insights into what happened when they encountered one another.
Neandertals were the first extinct hominin species to be recognized in the fossil record and the first to yield ancient DNA. Credit: Javier Trueba Science Source
The human saga, we now understand, is far more intricate than scholars of yore envisioned. The tidy tropes of our prehistory have collapsed under the weight of evidence: there is no single missing link that bridges apes and humankind, no drumbeat march of progress toward a predestined goal. Our story is complicated, messy and random. Yet it still can be accommodated under Darwin’s theory of evolution and in fact further validates that framework.
This is not to say scientists have it all figured out. Many questions remain. But whereas the origin of humans was once an uncomfortable speculation in Darwin’s big idea, it is now among the best-documented examples of evolution’s transformative power.
We humans are strange creatures. We walk upright on two legs and possess supersized brains, we invent tools to meet our every need and express ourselves using symbols, and we have conquered every corner of the planet. For centuries scientists have sought to explain how we came to be, our place in the natural world.
This quest was often distorted by racist ideologies. Consider the era leading up to the birth of Darwin’s bombshell theory. In the 1830s, while a young Darwin was making his momentous voyage onboard the Beagle, a movement was underway to promote the idea that the various modern human groups around the globe—races—had separate origins. To build the case for polygenism, as the theory is known, scientists such as Samuel Morton in Philadelphia collected skulls from people across the world and measured their sizes and shapes, falsely believing those attributes to be proxies for intelligence. When they ranked the specimens from superior to inferior, Europeans would conveniently come out on top and Africans on the bottom. “There was a desire to provide scientific justification for political and power structures,” says anthropological geneticist Jennifer Raff of the University of Kansas. “It was science in the service of slavery and colonialism.”
Although Darwin’s work came down firmly on the side of monogenism—the idea that all humans share a common ancestor—it was nonetheless co-opted to support notions about racial superiority. Social Darwinism, for one, misapplied Darwin’s ideas about the struggle for existence in natural selection to human society, providing a pseudoscientific rationalization for social injustice and oppression. Darwin himself did not subscribe to such views. In fact, his opposition to slavery may have been a driving force in his research agenda, according to his biographers Adrian Desmond and James Moore.
By the time Darwin published The Descent of Man, in 1871, the idea that humans had evolved from a common ancestor with apes was already gaining traction in the scientific community thanks to books published in the 1860s by English biologist Thomas Henry Huxley and Scottish geologist Charles Lyell. Still, the fossil evidence to support this claim was scant. The only hominin fossils known to science were a handful of remains a few tens of thousands of years old that had been recovered from sites in Europe. Some were H. sapiens; others would eventually be recognized as a separate but very closely related species, Homo neanderthalensis. The implication was that fossils of more apelike human ancestors were out there somewhere in the world, awaiting discovery. But the suggestion by Darwin, like Huxley before him, that those ancestors would be found in Africa met with resistance from scholars who saw Asia as a more civilized birthplace for humankind and emphasized similarities between humans and Asia’s gibbons.
Perhaps it should come as no surprise, then, that when the first hominin fossil significantly older and more primitive than those from Europe turned up, it came not from Africa but from Asia. In 1891 Dutch anatomist Eugène Dubois discovered remains on the Indonesian island of Java that he thought belonged to the long-sought missing link between apes and humans. The find, which he named Pithecanthropus erectus, spurred further efforts to root humankind in Asia. (We now know that Dubois’s fossil was between 700,000 and one million years old and belonged to a hominin that was much more humanlike than apelike, Homo erectus.)
Two decades later the search turned to Europe. In 1912 amateur archaeologist Charles Dawson reported that he had found a skull with a humanlike cranium and an apelike jaw in an ancient gravel pit near the site of Piltdown in East Sussex, England. Piltdown Man, as the specimen was nicknamed, was a leading contender for the missing link until it was exposed in 1953 as a fraudulent pairing of a modern human skull with an orangutan’s lower jaw.
Piltdown so seduced scholars with the prospect of making Europe the seat of human origins that they all but ignored an actual ancient hominin that turned up in Africa, one even older and more apelike than the one Dubois discovered. In 1925, 43 years after Darwin’s death, anatomist Raymond Dart published a paper describing a fossil from Taung, South Africa, with an apelike braincase and humanlike teeth. Dart named that fossil—a youngster’s skull now known to be around 2.8 million years old—Australopithecus africanus, “the southern ape from Africa.” But it would take nearly 20 years for the scientific establishment to accept Dart’s argument that the so-called Taung Child was of immense significance: the fossil linked humans to African apes.
Evidence of humanity’s African origins has accumulated ever since. Every hominin trace older than 2.1 million years—and there are now quite a few of them—has come from that continent.
Even as fossil discoveries proved Darwin right about the birthplace of humanity, the pattern of our emergence remained elusive. Darwin himself depicted evolution as a branching process in which ancestral species divide into two or more descendant species. But a long-standing tradition of organizing nature hierarchically—one that dates back to Plato and Aristotle’s Great Chain of Being—held sway, giving rise to the notion that our evolution unfolded in linear fashion from simple to complex, primitive to modern. Popular imagery reflected and reinforced this idea, from a caricature in Punch’s Almanack for 1882 showing a progression from earthworm to Darwin, to the iconic monkey-to-man illustration that appeared in the 1965 Time-Life book Early Man and became known as the March of Progress.
From the rich assortment of fossils and artifacts recovered from around the world in the past century, however, paleoanthropologists can now reconstruct something of the timing and pattern of human evolution. The finds clearly show that this single-file scheme is no longer tenable. Evolution does not march steadily toward predetermined goals. And many hominin specimens belong not in our direct line of ancestry but on side branches of humankind—evolutionary experiments that ended in extinction.
From the outset, our defining traits evolved not in lockstep but piecemeal. Take our mode of locomotion, for example. H. sapiens is what anthropologists call an obligate biped—our bodies are built for walking on two legs on the ground. We can climb trees if we need to, but we have lost the physical adaptations that other primates have to arboreal life. Fragmentary fossils of the oldest known hominins—Sahelanthropus tchadensis from Chad, Orrorin tugenensis from Kenya and Ardipithecus kadabba from Ethiopia—show that our earliest ancestors emerged by around seven million to 5.5 million years ago. Although they are apelike in many respects, all of them exhibit characteristics associated with walking on two legs instead of four. In Sahelanthropus, for example, the hole in the base of the skull through which the spinal cord passes has a forward position suggestive of an upright posture. A bipedal gait may thus have been one of the very first traits that distinguished hominins from ancestral apes.
Yet our forebears appear to have retained traits needed for arboreal locomotion for millions of years after they first evolved the ability to walk on two legs. Australopithecus afarensis, which lived in eastern Africa from 3.85 million to 2.95 million years ago and is famously represented by the skeleton known as Lucy, discovered in 1974, was a capable biped. But it had long, strong arms and curved fingers—features associated with tree climbing. It would be another million years before modern limb proportions evolved and committed hominins to life on the ground, starting with early H. erectus in Africa (sometimes called Homo ergaster).
The brain evolved on quite a different schedule. Over the course of human evolution, brain size has more than tripled. A comparison of the braincase of A. afarensis with that of the much older Sahelanthropus, however, shows that hardly any of that growth occurred in the first few million years of human evolution. In fact, most of the expansion took place in the past two million years, perhaps enabled by a feedback loop in which advances in technology—stone tools and the like—gave hominins access to more nutritious foods such as meat, which could fuel a larger and thus more energetically demanding brain, which in turn could dream up even better technology, and so on. Shifts in the shape and structure of the brain accompanied these gains, with more real estate allocated to regions involved in language and long-range planning, among other advanced cognitive functions.
This mosaic pattern of hominin evolution in which different body parts evolved at different rates produced some surprising creatures. For instance, Australopithecus sediba from South Africa, dated to 1.98 million years ago, had a humanlike hand attached to an apelike arm, a big birth canal but a small brain, and an advanced ankle bone connected to a primitive heel bone.
Sometimes evolution even doubled back on itself. When one examines a hominin fossil, it can be difficult to discern whether the species retained a primitive trait such as small brain size from an earlier ancestor or whether it lost the characteristic and then re-evolved it. But the strange case of Homo floresiensis may well be an example of the latter. This member of the human family lived on the island of Flores in Indonesia as recently as 50,000 years ago yet looked in many ways like some of the founding members of our genus who lived more than two million years earlier. Not only did H. floresiensis have a small body, but it also possessed a remarkably tiny brain for Homo, about the size of a chimp’s. Scientists’ best guess is that this species descended from a brawnier, brainer Homo species that got marooned on Flores and evolved its diminutive size as an adaptation to the limited food resources available on its island home. In so doing, H. floresiensis seems to have reversed what researchers once considered a defining trend of Homo’s evolution: the inexorable expansion of the brain. Yet despite its small brain, H. floresiensis still managed to make stone tools, hunt animals for food and cook over fires.
Adding to the complexity of our story, it is now clear that for most of the time over which humans have been evolving, multiple hominin species walked the earth. Between 3.6 million and 3.3 million years ago, for example, at least four varieties of hominins lived in Africa. Paleoanthropologist Yohannes Haile-Selassie of Arizona State University’s Institute of Human Origins and his colleagues have recovered remains of two of them, A. afarensis and Australopithecus deyiremeda, as well as a possible third creature known only from a distinctive fossil foot, in an area called Woranso-Mille in Ethiopia’s Afar region. How they managed to share the landscape is a subject of current investigation. “Competing species could co-exist if there were plenty of resources or if they were exploiting different parts of the ecosystem,” Haile-Selassie says.
Later, between roughly 2.7 million and 1.2 million years ago, representatives of our genus, Homo—large-brained tool users with dainty jaws and teeth—shared the grasslands of southern and eastern Africa with a radically different branch of humanity. Members of the genus Paranthropus, these hominins had massive teeth and jaws, flaring cheek bones and crests atop their heads that anchored powerful chewing muscles. Here the co-existence is somewhat better understood: whereas Homo seems to have evolved to exploit a wide variety of plants and animals for food, Paranthropus specialized in processing tough, fibrous plant foods.
H. sapiens overlapped with other kinds of humans, too. When our species was evolving in Africa 300,000 years ago, several other kinds of hominins also roamed the planet. Some, such as the stocky Neandertals in Eurasia, were very close relatives. Others, including Homo naledi in South Africa and H. erectus in Indonesia, belonged to lineages that diverged from ours in the deep past. Even as recently as 50,000 years ago, hominin diversity was the rule, with the Neandertals, the mysterious Denisovans from Asia, tiny H. floresiensis and another small hominin—the recently discovered Homo luzonensis from the Philippines—all at large.
Such discoveries make for a much more interesting picture of human evolution than the linear account that has dominated our view of life. But they raise a nagging question: How did H. sapiens end up being the sole surviving twig on what was once a luxuriant evolutionary bush?
Here are the facts of the case. We know from fossils found at the site of Jebel Irhoud in Morocco that our species originated in Africa by at least 315,000 years ago. By around 200,000 years ago it began making forays out of Africa, and by 40,000 years ago it had established itself throughout Eurasia. Some of the places H. sapiens colonized were occupied by other hominin species. Eventually the other folks all disappeared. By around 30,000 to 15,000 years ago, with the end of the Neandertals in Europe and the Denisovans in Asia, H. sapiens was alone in the world.
Researchers have often attributed the success of our species to superior cognition. Although the Neandertals actually had slightly larger brains than ours, the archaeological record seemed to indicate that only H. sapiens crafted specialized tools and used symbols, suggesting a capacity for language. Perhaps, the thinking went, H. sapiens won out by virtue of sharper foresight, better technology, more flexible foraging strategies and bigger social networks for support against hard times. Alternatively, some investigators have proposed, maybe H. sapiens waged war on its rivals, exterminating them directly.
But recent discoveries have challenged these scenarios. Neandertal technology, archaeologists have learned, was far more varied and sophisticated than previously thought. Neandertals, too, made jewelry and art, crafting pendants from shells and animal teeth and painting abstract symbols on cave walls. Moreover, they may not have been our only enlightened kin: a 500,000-year-old engraved shell from Java suggests that H. erectus also possessed symbolic thought. If archaic hominins had many of the same mental faculties as H. sapiens, why did the latter prevail?
The conditions under which H. sapiens got its start may have played a role. Fossil and archaeological data suggest that our species mostly stayed in Africa for the first couple of hundred thousand years of its existence. There, some experts argue, it evolved as a population of interconnected subgroups spread across the continent that split up and reunited again and again over millennia, allowing for periods of evolution in isolation followed by opportunities for interbreeding and cultural exchange. This evolutionary upbringing may have honed H. sapiens into an especially adaptable hominin. But that is not the whole story, as we now know from genetics.
Analyses of DNA have revolutionized the study of human evolution. Comparing the human genome with the genomes of the living great apes has shown conclusively that we are most closely related to chimpanzees and bonobos, sharing nearly 99 percent of their DNA. And large-scale studies of DNA from modern-day human populations across the globe have illuminated the origins of modern human variation, overturning the centuries-old notion that races are biologically discrete groups with separate origins. “There have never been pure populations or races,” Raff says. Modern human variation is continuous, and most variation actually exists within populations rather than between them—the product of our demographic history as a species that originated in Africa with populations that mixed continuously as they migrated around the world.
More recently, studies of ancient DNA have cast new light on the world of early H. sapiens as it was when other hominin species were still running around. In the late 1990s geneticists began recovering small amounts of DNA from Neandertal and early H. sapiens fossils. Eventually they succeeded in getting entire genomes not only from Neandertals and early H. sapiens but also from Denisovans, who are known from just a few fragmentary fossils from Siberia and Tibet. By comparing these ancient genomes with modern ones, researchers have found evidence that our own species interbred with these other species. People today carry DNA from Neandertals and Denisovans as a result of these long-ago encounters. Other studies have found evidence of interbreeding between H. sapiens and unknown extinct hominins from Africa and Asia for whom we have no fossils but whose distinctive DNA persists.
Mating with other human species may have aided H. sapiens’ success. Studies of organisms ranging from finches to oak trees have shown that hybridization with local species can help colonizing species flourish in novel environments by giving them useful genes. Although scientists have yet to figure out the functions of most of the genes people today carry from extinct hominins, they have pinpointed a few, and the results are intriguing. For instance, Neandertals gave H. sapiens immunity genes that may have helped our species fend off novel pathogens it encountered in Eurasia, and Denisovans contributed a gene that helped people adapt to high altitudes. H. sapiens may be the last hominin standing, but it got a leg up from its extinct cousins.
Scientists have many more pieces of the human-origins puzzle than they once did, but the puzzle is now vastly bigger than it was previously understood to be. Many gaps remain, and some may never close. Take the question of why we evolved such massive brains. At around 1,400 grams, the modern human brain is considerably larger than expected for a primate of our body size. “The singularity is why it’s interesting—and why it’s impossible to answer scientifically,” Wood observes. Some experts have suggested that hominin brains ballooned as they adapted to climate fluctuations between wet and dry conditions, among other explanations. But the problem with trying to answer “why” questions about the evolution of our unique traits, Wood says, is that there is no way to evaluate the proposed explanations empirically. “There isn’t a counterfactual. We can’t go back to three million years ago and not change the climate.”
Other mysteries may yield to further investigation, however. For example, we do not yet know what the last common ancestor of humans and the Pan genus that includes chimps and bonobos looked like. Genomic and fossil data suggest that the two lineages diverged between eight million and 10 million years ago—up to three million years before the oldest known hominin walked the earth—which means that paleoanthropologists may be missing a substantial chunk of our prehistory. And they have hardly any fossils at all of Pan, which has been evolving along its own path just as long as we have. Insights may come from a project currently underway in central Mozambique, where Susana Carvalho and René Bobe of the University of Oxford and their colleagues are hunting for fossil primates, including hominins, in sediments older than the ones that yielded Sahelanthropus, Orrorin and Ardipithecus.
Later stages of the human story are riddled with unknowns, too. If H. sapiens was interbreeding with the other hominin species it encountered, as we now know it was, were these groups also exchanging culture? Might H. sapiens have introduced Neandertals to novel hunting technology and artistic traditions—or vice versa? New techniques for retrieving ancient DNA and proteins from otherwise unidentifiable fossils and even cave sediments are helping researchers determine which hominin species were active and when at key archaeological sites.
One wonders where the next discovery will take us in the quest to understand who we are and where we come from. We may have found our place in nature, located our twig on the shrub, but we are still searching for ourselves. We’re only human, after all.