Population genomic assessments of the plausibility of evolutionary ecology hypotheses for human rainforest hunter-gatherers

Open Access
Author:
Cohen, Jacob Aubrey
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • George H Perry, Thesis Supervisor
  • Katriona Shea, Honors Advisor
Keywords:
  • rainforest hunter-gatherer
  • pygmy phenotype
  • convergent evolution
  • polygenic adaptation
  • ecology
Abstract:
Over the course of human history, genetically distinct hunter-gatherer populations in the tropical rainforests of Africa, Southeast Asia, and South America have evolved small stature, or the “pygmy” phenotype. There are many hypotheses, but no concrete answers, as to why this phenotype evolved convergently, in similar habitats, across the world. Recent research has identified multiple regions of the genome associated with the pygmy phenotype in the Batwa, a rainforest hunter-gatherer population from Uganda. This work also identified a signature of polygenic adaptation, or relatively subtle shifts in allele frequency in aggregate across a set of loci associated with a phenotype, for the pygmy phenotype-associated regions in the Batwa. In my honors thesis study, I analyzed population genomic data from the Batwa, a second rainforest hunter gatherer population from Cameroon, and the agriculturalist neighbors of each these two populations. I tested a hypothesis of neutrality vs. polygenic adaptation for sets of genes involved in functions relevant to various ecological hypotheses for the adaptive origins of small body size in the tropical rainforest (but not body size itself): food limitation/metabolism, thermoregulation, mobility/movement, and life history. If rainforest hunter-gatherer-specific signatures of polygenic adaptation are observed in any of these gene sets, then this would establish the evolutionary relevance of the related ecological factors in rainforest hunter-gatherer populations (although the potential role(s) of these factors in the evolution of the pygmy phenotype could not be confirmed directly with this approach). Concrete evidence of polygenic adaptation was not found; that is, the null hypothesis of neutral evolution could not be rejected for any gene set following correction for multiple tests. I do discuss two of the gene groups showing a trend towards statistical significance, and opportunities for further study.