From Oxford U: Bridging the bonding gap: the transition from primates to humans

http://www.ncbi.nlm.nih.gov/pubmed/22641822

Philos Trans R Soc Lond B Biol Sci. 2012 Jul 5;367(1597):1837-46.

Bridging the bonding gap: the transition from primates to humans.

Dunbar RI.

Source

British Academy Centenary Research Project, Institute of Cognitive and Evolutionary Anthropology, University of Oxford, , 64 Banbury Road, Oxford OX2 6PN, UK.

Abstract

Primate societies are characterized by bonded social relationships of a kind that are rare in other mammal taxa. These bonded relationships, which provide the basis for coalitions, are underpinned by an endorphin mechanism mediated by social grooming. However, bonded relationships of this kind impose constraints on the size of social groups that are possible. When ecological pressures have demanded larger groups, primates have had to evolve new mechanisms to facilitate bonding. This has involved increasing the size of vocal and visual communication repertoires, increasing the time devoted to social interaction and developing a capacity to manage two-tier social relationships (strong and weak ties). I consider the implications of these constraints for the evolution of human social communities and argue that laughter was an early evolutionary innovation that helped bridge the bonding gap between the group sizes characteristic of chimpanzees and australopithecines and those in later hominins.