Summary: New genomic analyses illuminate the genetic variations linked to social behavior differences among modern humans, archaic humans, and other primates.
Source: University of Barcelona
Modern humans are notable for pronounced prosocial traits — empathy, social tolerance, cooperation and altruism — which shape our complex societies.
Many aspects of social cognition have been associated with variation in the oxytocin and vasotocin signaling system, particularly the oxytocin receptor (OTR) and vasotocin/vasopressin receptors (VTR/AVPR). Understanding how variation in these genes evolved can help explain behavioral differences across hominins and other primates.
To explore this, researchers at the University of Barcelona and Rockefeller University compared available genomic sequences for these receptor genes across modern humans, several non-human primate species (including chimpanzees, bonobos and macaques) and, for the first time in this context, archaic humans by using all accessible Neanderthal and Denisovan genomes.
Published in Comprehensive Psychoneuroendocrinology, the study identifies genomic sites where modern humans differ from both archaic humans and non-human primates, as well as sites shared by modern and archaic humans but absent from other primates. The analyses combine genomics, population genetics, transcriptomics and behavioral neuroscience to link genetic variation with social behavior.
“We used an interdisciplinary approach to trace the evolution of hominid prosociality through oxytocin and vasotocin receptors, integrating modern and archaic genomes with functional and behavioral evidence,” explains first author Constantina Theofanopoulou.
This work forms part of Theofanopoulou’s doctoral research, co-supervised by Cedric Boeckx (ICREA, Institute of Complex Systems, UB) and Erich D. Jarvis (Rockefeller University).
Modern-human–specific variants common in global populations
The team focused on polymorphic heterozygous sites — genome positions where more than one allele exists within a population — rather than only fixed differences. Previous whole-genome comparisons often sought sites that were nearly fixed in modern humans relative to Neanderthals or chimpanzees. In contrast, this study examined positions where a major allele is present in a substantial portion of modern humans (for example, >70%), even if it is not universal.
They identified five sites across OTR, VTR1A and VTR1B where one modern human variant is distinct from both archaic humans and other primates and where that variant is the major allele in over 70% of today’s global population. Functional analyses indicate several of these variants likely affect receptor function, and regulatory data show these loci lie in genomic regions active in the brain — notably the cingulate gyrus, which is important for social cognition.
These modern-human–specific variants have also been linked in other studies to social behaviors and neurodevelopmental conditions characterized by social deficits, including autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD) and aggression. Such associations suggest these genetic changes could contribute to behavioral differences inferred between modern humans and archaic hominins.
“These differences may relate to the smaller social group sizes proposed for Neanderthals and Denisovans, altered androgen-related traits, or differing social structures such as polygyny and increased male–male competition in some archaic populations,” Theofanopoulou notes.
Variants shared by modern and archaic humans
The study also found two OTR sites where modern and archaic humans share alleles not found in other primates; both alleles occur at high frequencies in present-day humans (>85%). One of these sites was predicted to be highly functional. The presence of shared modern–archaic variants suggests some changes in social biology preceded the split between Homo sapiens and other hominins and may have supported greater social tolerance and cultural transmission, such as technology sharing and cooperative behaviors.
Convergent changes with bonobos
Interestingly, researchers identified three positions where modern humans and bonobos — a primate species known for comparatively high social tolerance and cooperative behavior — carry the same nucleotide. These convergent sites may help explain parallel traits in prosociality, attentiveness to faces and eyes, and empathic sensitivity observed in bonobos and humans, as compared to chimpanzees.
All sites highlighted in the study have prior independent links to social behavior and neurodevelopmental disorders involving social deficits. Viewing developmental disorders through an evolutionary lens — an evo-devo perspective — could help prioritize genetic loci for clinical research and potentially support earlier diagnosis by revealing evolutionary patterns that pinpoint candidate variants.
Next steps and broader genetic context
Future work will test these findings in larger samples. Increasing sample size is relatively easier for extant primates such as chimpanzees and bonobos but remains constrained for Neanderthals and Denisovans, where new data depend on archaeological discoveries and ancient DNA recovery. Researchers also plan to broaden the scope beyond oxytocin and vasotocin pathways to include other genes implicated in human social evolution, such as dopamine-related loci.
About this oxytocin and social neuroscience research news
Author: Rosa Martínez
Source: University of Barcelona
Contact: Rosa Martínez – University of Barcelona
Image: The image is in the public domain
Original Research: Open access. “Oxytocin and vasotocin receptor variation and the evolution of human prosociality” by Constantina Theofanopoulou et al., Comprehensive Psychoneuroendocrinology
Abstract
Oxytocin and vasotocin receptor variation and the evolution of human prosociality
Modern human societies rely heavily on complex social traits such as empathy, tolerance and cooperation. Variation in the oxytocin receptor (OTR) and related vasotocin/vasopressin receptors (VTR1A/AVPR1A and VTR1B/AVPR1B) has been linked to these social behaviors. This study compared receptor gene sequences across modern humans, archaic humans and 12 non-human primate species to identify heterozygous sites where variation in hominins differs from other primates and where clinical association data exist.
Across these sites the authors performed analyses including variant clustering, pathogenicity prediction, regulatory impact and linkage disequilibrium and reviewed selection signals in diverse modern-human populations. They report five modern-human–specific variants (OTR: rs1042778, rs237885, rs6770632; VTR1A: rs10877969; VTR1B: rs33985287), with OTR-rs6770632 predicted as highly functional. Two alleles (OTR: rs59190448 and rs237888) shared by modern and archaic humans appear to be under positive selection, and three loci show convergent evolution between modern humans and bonobos (OTR: rs2228485, rs237897; VTR1A: rs1042615). OTR-rs2228485 ranked highly for functionality and has evidence of balancing selection in modern humans.
These results have implications for understanding the genetic changes that shaped hominid prosociality and the behavioral parallels between modern humans and bonobos.