1Departments of Anthropology and Biology, Pennsylvania State University, 2DFG Center for Advanced Studies “Words, Bones, Genes, Tools”, University of Tübingen, 3Research Centre in Evolutionary Anthropology and Palaeoecology, Liverpool John Moores University
April 17, 2020 , Platinum Ballroom
Bipedalism is hypothesized to have had an evolutionary impact on human parturition. Specifically, the morphology of the human pelvis that permits habitual bipedalism may also constrain fetal brain and body size, a phenomenon known as the obstetric dilemma. Some of the assumptions behind this model have been questioned by recent work, but the genetic mechanisms underlying the potential coevolution of these traits remain largely unknown. Here we use a GWAS approach and the UKBiobank dataset to test whether two proxies for the obstetric dilemma (female hip circumference and first child birth weight) are associated with the same genetic variants in a pleiotropic manner. Using genotype-phenotype data, we identified 148 single nucleotide polymorphisms (SNPs) significantly associated with female hip circumference and 49 SNPs significantly associated (P<5x10-8) with first child birth weight. Of these SNPs, 9 influence both women’s hip circumference and first child birth weight, suggesting pleiotropic impacts on the traits. We further found that SNPs significantly associated with female hip circumference causally affect first child birth weight (P=3.88x10-5), but not vice versa (P=0.449). Using the singleton density score statistic, which evaluates polygenic trait-associated allele frequency changes, we observe tentative evidence of recent (past ~3000 years) positive selection on SNP alleles associated with increased women’s hip circumference (P=0.0381), but no evidence of selection on first child birth weight (P=0.3516). Overall, these results suggest that increased female hip circumference may have been a target of recent positive selection in the UK population, potentially resulting in a pleiotropic increase in offspring birth weight.
The Penn State University Erickson Discovery, Presidential Leadership Academy Enrichment, and Liberal Arts Enrichment Grants (all to A.M.A); NIH grant R01-GM115656 (to G.P); and DFG grant FOR-2237.