Modern humans are characterized by their prosociality, a broad term that encompasses intraspecies empathy, social tolerance, cooperation and altruism. These facets of social cognition have been associated with variations in the oxytocin and vasotocin genes (OT and VT) and their receptors (OTR and VTR).To shed light on the genetic basis of this behaviour, scientists from the University of Barcelona (UB) and Rockefeller University carried out a new study comparing the available genomic sequences of these genes between modern humans, non-human primate species (e.g., chimpanzees, bonobos, and macaques) and, for the first time, archaic humans, using all the available genomes of Neanderthals and Denisovans.
In the study, published in the journal Comprehensive Psychoneuroendocrinology, the researchers identified several sites in which modern humans differed from both archaic humans and non-human primates, and others where both modern and archaic humans differed from non-human primates.
“We used an interdisciplinary approach to understand the evolution of hominid prosociality through the lens of the oxytocin and vasotocin receptors, where we combined evidence from modern and archaic genomics, population genetics, transcriptomics, and behavioural and neuroscientific studies, among other methods. These results can shed light on the genetics underlying possible sociality differences identified between modern humans and archaic humans, as well as the similarities between the modern human and bonobo social behaviour,” said first author Constantina Theofanopoulou. This research is part of her doctoral thesis carried out under the co-supervision of Cedric Boeckx, ICREA researcher at the Institute of Complex Systems at the UB (UBICS) and Erich D. Jarvis, professor at Rockefeller University.
Variants unique to modern humans in more than 70% of the population
Considering the evidence on modern human prosociality and on the involvement of the oxytocin and vasotocin genes in social behaviours, the researchers hypothesized that the evolution of these genes might elucidate the genetic basis of the evolution of hominin prosociality. With this aim in mind, the study explored the differences between modern humans, archaic humans and non-human primates in polymorphic heterozygous sites in the human genome — locations where at least two alternative sequences are found in a population. “Past studies that compared the entire modern human genome with the Neanderthal or the chimpanzee genomes have focused on changes that are fixed or nearly fixed in modern humans. This has led to them identifying sites where, for example, all Neanderthals had Adenine (one of the four nucleotides that with guanine, cytosine and thymine form the DNA) and nearly all modern humans (say, 98%) have Guanine. In this study, we searched for differences on locations where, by definition, not all modern humans share the same nucleotide, namely on polymorphic sites, where for example, 70% of the modern human population has Adenine and 30% Cytosine,” adds Theofanopoulou.
The researchers identified five sites in the oxytocin and vasotocin receptors where modern humans are unique in one of their two (or more) variants compared to archaic humans and non-human primates, and which are at the same time found in more than 70% of the modern human population. Next, they conducted functional and frequency analyses to establish whether the variants are relevant. They performed a range of analyses on the five sites and found that some of the variants are highly functional, indicating that they have an effect on the molecular function of the proteins activated by these genes.
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