This is where
genetic effects and
trends attract
environmental influences on an
organism. The clearest occurrence of this in
humans is associated with
gender. Gender is determined purely by genetics, but gender determines how a
person is treated in
society.
Boys are raised differently to
girls, they will be given different
toys and they will wear different
clothes and so forth. Although there are differences in the
psyche of the
male and
female, these are exacerbated by their
roles in society.
Other less obvious examples of gene-environment covariance include people with a genetic intolerance for alcohol. Such people will decline offers of drinks to avoid becoming ill. Also, children with a genetic tendency which promotes studiousness, will enjoy school and excel in an academic environment.
Such effects help to resolve the nature or nurture debate in developmental psychology. The evidence, as with so many things, points to some sort of middle-ground, with genetics and environment interacting closely rather than one predominating over the other.