Polygyny – maybe it’s agriculture

Citation: Lippold, Sebastian, et al. "Human paternal and maternal demographic histories: 4 insights from high-resolution Y chromosome and mtDNA sequences 5." Methods 1 (2014): 2.
Citation: Lippold, Sebastian, et al. “Human paternal and maternal demographic histories: 4 insights from high-resolution Y chromosome and mtDNA sequences 5.” Methods 1 (2014): 2.

Alexander Kim has already responded in depth to a new paper in Investigative Genetics, Human paternal and maternal demographic histories: insights from high-resolution Y chromosome and mtDNA sequences:

We identified 2,228 SNPs in the NRY sequences and 2,163 SNPs in the mtDNA sequences. Our results confirm the controversial assertion that genetic differences between human populations on a global scale are bigger for the NRY than for mtDNA, although the differences are not as large as previously suggested. More importantly, we find substantial regional variation in patterns of mtDNA versus NRY variation. Model-based simulations indicate very small ancestral effective population sizes (<100) for the out-of-Africa migration as well as for many human populations. We also find that the ratio of female effective population size to male effective population size (Nf/Nm) has been greater than one throughout the history of modern humans, and has recently increased due to faster growth in Nf than Nm.

The NRY and mtDNA sequences provide new insights into the paternal and maternal histories of human populations, and the methods we introduce here should be widely applicable for further such studies.

Comparing male and female demographic histories can be a mug’s game. But if one is appropriately cautious some insight can be gained, and in this paper the authors are appropriately cautious. It isn’t surprising that female effective population sizes are somewhat larger over the long term and across deep history than male ones for our lineage. We’re a mildly sexually dimorphic species, suggestive of possible mild polygyny at best, on average. In other words, males compete, but not that much. Far more interesting to me is what Alexander Kim keys in on:

Among the most interesting inferences is Holocene crash in male Ne, with no clear reflection on the mitochondrial side of things, everywhere but Oceania and America — most dramatically in the Middle East/North Africa:

Not from the Pleistocene
Not from the Pleistocene

As a speculative matter this might reflect the rise of “super-male” lineages that arose with agriculture and mass society. In other words, extreme levels of polygyny are a novel cultural evolution, which could only emerge with the level of stratification and power accumulation in patrilineages enabled by agricultural, or agro-pastoral, societies. Hyper-polgyny might also be correlated with the extreme mate guarding and sexual jealousy which is the norm among many Eurasian societies. The implication here is that many of the “regressive” social practices we associate with “traditional” Eurasian societies are simply cultural retrofits to adapt to new social circumstances enabled by mass society. Liberal individualism as an ethos may not be a novel innovation, as much as the emergence of long submerged instincts which evolved when collective institutions and interests were far weaker as forces in our day to day decision making.

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