3 Genotype-Environment Effects

It has long been realized that the distinction we make for heuristic purposes between ``genotype'' and ``environment'' is an approximation which ignores several processes that might be important in human populations. Three factors defy the simple separation of genetic and environmental effects, but are likely to be of potential significance from what we know of the way genes operate in other species, and from the logical consequences of the grouping of humans into families of self-determining individuals who share both genes and environment in common. The factors we need to consider are:

1. assortative mating
2. genotype-environment covariance (CovGE, or genotype-environment correlation, CorGE)
3. genotype $\times$ environment interaction (G$\times$E).

Each of these will be discussed briefly.