  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.
