Friday, 3 June 2022

Evolution News - How Humans Evolved Social Behaviour and Cooperation

Neanderthals may have had less prosocial behaviour than modern humans. They had smaller social groups and may have had a polygynous social structure with more male-male competition.
What oxytocin can tell us about the evolution of human prosociality - Universitat de Barcelona

One of the more nonsensical creationist talking points you still hear occasionally, is that evolution can't account for altruism because survival of the fittest means the selfish survive at the expense of others less selfish. This is demonstrably untrue because the result of evolution show that cooperation at all levels of organisation, from intracellular organelles to social groups of multicellular organisms, is better than conflict, and human society especially demonstrates the truth of this where any tendency towards freeloading is moderated by social ethics and the affiliative needs of individuals.

Now this reasoning has been supported by research which shows that human evolution included improving the ability to empathize. Empathy, of course, is the basis for all human prosocial behaviour and is even acknowledged in the Judaeo-Christian holy books with the invocation to do unto others that which you would they do unto you - the 'golden rule', common to all human societies.

Modern human societies are characterised by comparatively high levels of prosocial behaviours such as intraspecies empathy, social tolerance, cooperation and altruism. Now, Constantina Theofanopoulou, as part of her doctoral thesis carried out under the co-supervision of Cedric Boeckx, ICREA researcher at the Institute of Complex Systems at the Universitat de Barcelona (UBICS) and Erich D. Jarvis, professor at Rockefeller University, has shown that this has an evolved genetic basis involving the genes that control oxytocin and vasotocin receptor in the brain. Oxytocin, also known as the 'love' hormone, is responsible for social bonding as well as sexual attraction and parent-child bonding.

By analysing the genomes of modern humans, Neanderthals and Denisovans as well as non-human primates, the common chimpanzees, bonobos and macaques, Theofanopoulou and her colleagues have shown that there are 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.

The scientists have published their finding's, open access, in the journal, Comprehensive Psychoneuroendocrinology.

The Universitat de Barcelona news release gives more details:
Variants unique to modern humans in more than 70% of the 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.

[the differences] might be relevant to the smaller social groups attributed to Neanderthals and Denisovans or to the decreased modern human androgenization. They might also be relevant to a different social structure, i.e., Neanderthals have been linked to a polygynous social structure and a higher level of male–male competition than most contemporary modern human populations.

The sites that are unique in both us and archaic humans versus non-human primates can elucidate the genetic underpinnings of the progressive social tolerance needed for the intensive cultural transmission of technological innovations (e.g., fire use) in the evolution of humankind, as well as for the reduced aggression indicated by several markers in early hominid evolution, such as the reduction of male canine size and the accelerated demographic success.

The convergent sites in modern humans and bonobos could be insightful for understanding the posited similarities in prosociality, social tolerance and cooperation between us and bonobos, and the differences of both compared to chimpanzees. For example, bonobos outperform chimpanzees on tasks relevant to social causality or theory of mind and are more attentive to the face and eyes, suggestive of higher empathic sensitivity.

Understanding developmental disorders through evolutionary lenses can aid into us achieving what we call an evo-devo (evolutionary and developmental biology) understanding of these disorders. If indeed “ontogeny recapitulates phylogeny”, then deciphering our evolutionary trajectory may shed light to new genetic spots for clinical research that might, in turn, lead to earlier disorder diagnosis.

Constantina Theofanopoulou, first author
PhD Candidate
Laboratory of Neurogenetics of Language
Rockefeller University, New York, USA
And Institute of Complex Systems
University of Barcelona
Catalonia, Spain
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.

The study compared 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.

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.

The researchers also found that these sites are encountered in genome regions that are active in the brain, particularly in the cingulate gyrus, a brain region involved in social cognition-relevant pathways. Moreover, all these sites have been associated in other studies with a plethora of social behaviours or social deficits, such as autism, attention deficit hyperactivity disorder (ADHD), aggression, and so on.

These findings may help to explain some of the social differences between modern humans and what we presume to know about the social behaviours of Neanderthals and Denisovans.

Variants present only in modern and archaic humans

The study also found two sites on the oxytocin receptor under a positive selection in modern and archaic humans: that is to say, modern and archaic humans showed a variant that was not present in any other non-human primate. This means that these sites are found in very high percentages in the modern human population (in this case, more than 85%). These same sites have also been associated with a great many social behaviours or deficits, and one of them was predicted to be a highly functional site in their regulation analyses.

Convergent sites with bonobos

Lastly, the researchers found three sites where modern humans and bonobos, a primate species that shows convergence of prosocial behaviours with humans, have the same nucleotide.

All the sites identified in this study have also been independently associated with disorders that include social deficits, such as autism spectrum disorders (ASD).
Because the same sites were not found in the common chimpanzees, with whom we share common ancestry with bonobos, the team reasoned that the three sites which humans and bonobos have in common is most likely a case of convergent evolution. This emphasises the selective advantage in this mutation in bonobos, in which prosocial, empathetic behaviour is highly developed.

More detail is given in the abstract and highlight section to their paper:
Copyright: © 2022 The authors.
Published by Elsevier B.V. Open access. (CC BY 4.0)
  • We compared the oxytocin/vasotocin receptors in modern humans, archaic humans, and non-human primates.
  • We found 5 sites with modern human specific variation.
  • In these sites, the modern human allele is the major allele in the global population.
  • Several sites were predicted to be functional and with selection signatures in modern humans.
  • We also identified 3 sites of convergent evolution in modern humans and bonobos.


Modern human lifestyle strongly depends on complex social traits like empathy, tolerance and cooperation. These diverse facets of social cognition have been associated with variation in the oxytocin receptor (OTR) and its sister genes, the vasotocin/vasopressin receptors (VTR1A/AVPR1A and AVPR1B/VTR1B). Here, we compared the available genomic sequences of these receptors between modern humans, archaic humans, and 12 non-human primate species, and identified sites that show heterozygous variation in modern humans and archaic humans distinct from variation in other primates, and for which we could find association studies with clinical implications. On these sites, we performed a range of analyses (variant clustering, pathogenicity prediction, regulation, linkage disequilibrium frequency), and reviewed the literature on selection data in different modern-human populations. We found five sites with modern human specific variation, where the modern human allele is the major allele in the global population (OTR: rs1042778, rs237885, rs6770632; VTR1A: rs10877969; VTR1B: rs33985287). Among them, variation in the OTR-rs6770632 site was predicted to be the most functional. Two alleles (OTR: rs59190448 and rs237888) present only in modern humans and archaic humans were putatively under positive selection in modern humans, with rs237888 predicted to be a highly functional site. Three sites showed convergent evolution between modern humans and bonobos (OTR: rs2228485 and rs237897; VTR1A: rs1042615), with OTR-rs2228485 ranking highly in terms of functionality and reported to be under balancing selection in modern humans (Schaschl, 2015) [1]. Our findings have implications for understanding hominid prosociality, as well as the similarities between modern human and bonobo social behavior.

It is entirely possible therefore that modern human groups were able to out-compete the archaic hominins because we were able to sustain larger cooperative groups, with reduced internal conflict stemming from male-male rivalry, than the archaic hominins could manage. This improved social cohesion gave us an evolutionary advantage, hence it came to predominate in the human gene pool, in a classic example of evolution by natural selection.

No doubt, despite evidence such as this to the contrary, we will still get creationists denying the common ancestry of humans and other apes and asserting that natural selection can't account for altruism and love because it would favour selfishness. Creationism requires its dupes to stay stoically ignorant of 'toxic' science. No doubt too that creationists will still make the increasingly forlorn claim that the TOE is a theory in crisis, despite the evidence such as that in this paper that it is fundamental to our understanding of biology and the only scientific theory that makes sense of the evidence without resorting to magical mysteries and childish fairy tales.

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