Culture-Genetic Models of Information Exchange in Humans: Integrating Genetic, Skeletal and Archaeological Data

Here, I test a model that attempts to explain the low genetic diversity and low effective population size of Homo sapiens though a model of Culturally Mediated Migration (CMM). This model posits that human genetic diversity has been reduced throughout the Pleistocene by an interaction of culture and gene flow. According to the CMM model, humans inevitably develop cultural practices that reduce gene flow between culturally different groups. In this restricted gene flow population, natural selection cannot spread favorable genes by simple diffusion across populations. Instead, favorable genes spread when the populations that carry them expand; displacing or replacing other populations. This process may reduce genetic diversity across the genome as a function of the successive replacements of most ancient populations. However, the model is untested. I derive expectations as to how the anthropological data (osteological, genetic, ethnographic, and archaeological) should be pattern if CMM is an accurate depiction for human behavior. I show that the archaeological data is patterned in the expected way: information follows between populations in ways expected based upon mediated migration. However, neither the skeletal data, the ethnographic, nor the genetic results support the tested hypothesis. I further investigate the force of natural selection in Neandertal populations, to assess the extent to which morphological characters may inform about ancient population sizes as opposed to natural selection. Models predicated on effective population size often misuse this genetic parameter. I further demonstrate that any model that limits the power of natural selection is inherently flawed, as Neandertals were subjected to this force to a greater extent than is often realized. This study uses multiple lines of anthropological data to test a genetic model of human evolution. Low human genetic diversity is symptomatic of the early human population as a whole and models explicating this genetic anomaly must take into account all of these factors. I show that information (both genetic and cultural) moved between regional populations to a greater degree than often recognized.