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The human behavioural immune system is a product of cultural evolution

Disgust is a basic emotion that serves to avoid contaminants, and is central to the behavioural immune system. While disgust-motivated avoidance occurs in bonobos and chimpanzees, humans show uniquely high levels of contamination sensitivity. Current theory postulates that human disgust is primarily a genetic adaptation, side-lining social transmission and denying parental modelling. Here, we test whether this strong view is warranted by simulating 100000 years of cultural and biological evolution in various scenarios. We modelled disgust as a trait that governed the extent to which individuals forewent potentially contaminated nutrition. This lowered their risk of gastrointestinal illness, at the cost of increasing starvation risk and birth-interval. As environmental levels and costs of contamination rose, so did relative fitness of high-disgust individuals. Evolutionary shifts in disgust as polygenic trait occurred as a consequence of germ-cell mutations, but were most prominent in populations with high initial genetic variance. Crucially, cultural transmission between generations operated at a higher rate, even if parental modelling was eliminated. This study serves not only as evidence of cultural evolution shaping the behavioural immune system, but also as an illustration of emerging theories that paint affective and cognitive mechanisms as socially transmitted rather than biologically determined functions.

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