The effect a gene has on a trait isn't equal in all environments. It plays a larger part in groups of people who have very similar environmental conditions, con

The effect a gene has on a trait isn't equal in all environments. It plays a larger part in groups of people who have very similar environmental conditions, conversely it plays a much smaller role in populations with a high variation in environmental conditions. We know that there is a fairly large variation in the environments of the groups you mentioned so it stands to reason the differences have very little to do with genetics. tl;dr go learn what heritability is.