The study was led by researchers from Northwest University in China and a team including the University of Bristol and the University of Western Australia, and examined how langurs and odd-nosed monkeys, part of the Asian colobine family, that can be found from tropical rainforests to snow-covered mountains, adapted over time.
These species were chosen by the researchers 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 from a common ancestral state to the diverse systems present today.
By integrating ecological, geological, fossil, behavioural and genomic analyses, the team found that colobine primates inhabiting colder environments tend to live in larger, more complex groups. More specifically, glacial periods during the past six million years promoted the selection of genes involved in cold-related energy metabolism and neuro-hormonal regulation.
They found that odd-nosed monkeys living in extremely cold locations had developed more efficient hormonal (dopamine and oxytocin) pathways that may lengthen maternal care, leading to longer periods of breast-feeding and an overall increase in infant survival. These adaptive changes also appear to 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.
Paper: Qi X-G et al. (2023). Adaptations to a cold climate promoted social evolution in Asian colobine primates. Science.