The neuropeptide arginine vasotocin (AVT; non-mammals) and its mammalian 
homologue, arginine vasopressin (AVP) influence a variety of sex-typical and 
species-specific behaviors, and provide an integrational neural substrate for 
the dynamic modulation of those behaviors by endocrine and sensory stimuli. 
Although AVT/AVP behavioral functions and related anatomical features are 
increasingly well-known for individual species, ubiquitous species-specificity 
presents ever increasing challenges for identifying consistent 
structure-function patterns that are broadly meaningful. Towards this end, we 
provide a comprehensive review of the available literature on social behavior 
functions of AVT/AVP and related anatomical characteristics, inclusive of 
seasonal plasticity, sexual dimorphism, and steroid sensitivity. Based on this 
foundation, we then advance three major questions which are fundamental to a 
broad conceptualization of AVT/AVP social behavior functions: (1) Are there 
sufficient data to suggest that certain peptide functions or anatomical 
characteristics (neuron, fiber, and receptor distributions) are conserved across 
the vertebrate classes? (2) Are independently-evolved but similar behavior 
patterns (e.g. similar social structures) supported by convergent modifications 
of neuropeptide mechanisms, and if so, what mechanisms? (3) How does AVT/AVP 
influence behavior - by modulation of sensorimotor processes, motivational 
processes, or both? Hypotheses based upon these questions, rather than those 
based on individual organisms, should generate comparative data that will foster 
cross-class comparisons which are at present underrepresented in the available 
literature.