Stepwise Evolution of Stable Sociality in Primates

Institute of Cognitive and Evolutionary Anthropology, 64 Banbury Road, University of Oxford, Oxford OX2 6PN, UK.
Nature (Impact Factor: 41.46). 11/2011; 479(7372):219-22. DOI: 10.1038/nature10601
Source: PubMed


Although much attention has been focused on explaining and describing the diversity of social grouping patterns among primates, less effort has been devoted to understanding the evolutionary history of social living. This is partly because social behaviours do not fossilize, making it difficult to infer changes over evolutionary time. However, primate social behaviour shows strong evidence for phylogenetic inertia, permitting the use of Bayesian comparative methods to infer changes in social behaviour through time, thereby allowing us to evaluate alternative models of social evolution. Here we present a model of primate social evolution, whereby sociality progresses from solitary foraging individuals directly to large multi-male/multi-female aggregations (approximately 52 million years (Myr) ago), with pair-living (approximately 16 Myr ago) or single-male harem systems (approximately 16 Myr ago) derivative from this second stage. This model fits the data significantly better than the two widely accepted alternatives (an unstructured model implied by the socioecological hypothesis or a model that allows linear stepwise changes in social complexity through time). We also find strong support for the co-evolution of social living with a change from nocturnal to diurnal activity patterns, but not with sex-biased dispersal. This supports suggestions that social living may arise because of increased predation risk associated with diurnal activity. Sociality based on loose aggregation is followed by a second shift to stable or bonded groups. This structuring facilitates the evolution of cooperative behaviours and may provide the scaffold for other distinctive anthropoid traits including coalition formation, cooperative resource defence and large brains.

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    • "Moreover, behavior does not fossilize, and social structure leaves no direct marks in the earth. This is why we must resort to the relationship between phylogenetic proximity and social organization in living primate species (Shultz et al. 2011). The hominin lineage branched off from the primate mainstream some 6.5 million years ago or earlier (Langergraber 2012; Wood 2010). "
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    • "pithecia) and the ruffed lemur (Varecia) also exhibited substantial flexibility. Our results are consistent with previous studies that have also found a phylogenetic component associated with aspects of social organization at the interspecific (Shultz et al. 2011) and intergeneric levels (DiFiore and Rendall 1994). It is important to note that while our predictive analyses " controlled for " phylogeny, phylogenetic signal can be quantified in a trait itself (in this case, social organization flexibility). "
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