Examining langurs and odd-nosed monkeys provided scientists with evidence that social behaviours, such as extended care by mothers, evolved by adapting to live in extremely cold climatic conditions in the long-run.
Other social behaviours that they studied included increased infant survival and being able to live in large complex multilevel societies.
The study was led by researchers from Northwest University in China and a team including the University of Bristol (UK) and the University of Western Australia, Australia. It is published in the journal Science.
These species, part of the Asian colobine family and found from tropical rainforests to snow-covered mountains, were chosen for the study as they exhibit four distinct types of social organisation and provide a good model for examining the multiple mechanisms that have driven their social evolution.
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The team integrated ecological, geological, fossil, behavioural and genomic analyses and found that colobine primates inhabiting colder environments tended to live in larger, more complex groups.
More specifically, they said, glacial periods of the last six million years promoted the selection of genes involved in cold-related energy metabolism and neuro-hormonal regulation.
Further, odd-nosed monkeys living in extremely cold locations had been found to develop more efficient hormonal (dopamine and oxytocin) pathways, possibly lengthening maternal care, longer breast-feeding periods and enhanced infant survival.
The scientists also think that these adaptive changes may have strengthened relationships between individuals, increased tolerance between males and enabled the evolution from independent one-male, multi-female groups to large complex multilevel societies.
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"Our study identified, for the first time, a genetically regulated adaptation linked to the evolution of social systems in primates.
"This finding offers new insights into the mechanisms that underpin behavioural evolution in primates and could be used to address social evolutionary changes across a wide range of species including humans," said Kit Opie, one of the study's authors from the Department of Anthropology and Archaeology at the University of Bristol.
"With climate change becoming an hugely important environmental pressure on animals, it is hoped that this study will raise awareness for the need to investigate what course social evolution will take as the prevailing climate changes.
"Our finding that complex multilevel societies have roots stretching back to climatic events in the distant evolutionary past also has implications for a reconstruction of the human social system which is decidedly multilevel," said Cyril Grueter, another author of the study from the Department of Anatomy, Physiology and Human Biology at the University of Western Australia, Australia.
