Razib Khan One-stop-shopping for all of my content

December 21, 2011

The arc of primate social evolution

A new paper in Nature, Stepwise evolution of stable sociality in primates, was written up in The New York Times with the provocative title, Genes Play Major Role in Primate Social Behavior, Study Finds. As noted in Joan Silk’s article on the paper it should really be phylogenetics play major role in primate social behavior. The model outlined in the paper indicates that phylogenetic relationships between major primate clades is a much better predictor of social organization and structure than simple adaptation to a specific environment, or a linear increase in social organization (group size) over time. Both of these latter dynamics would also be driven by genetic changes, and therefore tie “genes” to social behavior. In other words, genes always matter, it’s just how they matter that differs. Here’s the section of the abstract of the paper of major interest:

… 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….

I read the “letter,” but the reality is that this is one of those papers where you have to read the supplements to get a real sense of what is going on. I haven’t as of this moment, though I invite readers to browse through them and get back with their own assessment of the model. Broadly, I don’t object to the inference generated here…but I do wonder if the transition between the human-chimp ancestor and later hominins is to some extent sui generis. I have suggested that modern humans were “inevitable” after ~2 million years before the present, but I don’t think there was anything inevitable before that period. The overall point of the paper is that history and contingency matter a great deal, which to me implies that we should be cautious about making specific judgments of positions along the phylogenetic tree derived from what we gather from the whole….

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