Simulation of 100 000 years of evolution in hunter-gatherers: Evolutionary shifts in disgust as polygenic trait occurred (consequence of germ-cell mutations), but cultural transmission between generations operated more quickly & at greater magnitude

The human behavioural immune system is a product of cultural evolution. Edwin S. Dalmaijer, Thomas Armstrong. arXiv Dec 17 2021, https://arxiv.org/abs/2008.13211

Abstract: To avoid disease, humans show far greater contamination sensitivity and avoidance than their closest living relatives. This is driven by an increased propensity to experience disgust. There is broad agreement that uniquely sensitive disgust in humans is an evolutionary adaptation, which was previously thought to be fuelled by both cultural and genetic inheritance. However, current theories have centred biology and sidelined culture, despite surprisingly little empirical evidence to support this claim. Here, we simulated 100 000 years of evolution in human hunter-gatherers to directly compare genetic and cultural inheritance in a variety of scenarios. We modelled disgust avoidance as a trait that governed the extent to which individuals forewent potentially contaminated nutrition to avoid risking gastrointestinal illness. Our results confirmed natural selection for disgust, particularly as the level and cost of contamination in an environment increased. Evolutionary shifts in disgust as polygenic trait occurred as a consequence of germ-cell mutations, but were more prominent in populations with high initial genetic variance. Crucially, cultural transmission between generations operated more quickly and at greater magnitude, even if parental modelling was eliminated. Our computational work supports the hypothesis that cultural evolution outpaced its biological counterpart to select health-improving behaviours that benefited survival. This study serves not only as evidence of cultural evolution shaping the behavioural immune system, but is also an illustration of emerging theories that paint affective and cognitive mechanisms as socially transmitted rather than biologically determined functions.