Nature + Nurture is a model
Aamodt and Wang in the NYTimes:
Much more than depression is partly inherited. Here’s a weirder fact: the genes you get from your parents partly determine your risk of being mugged. So do genes dictate our fate? Of course not — but they do have a say in who we become.
Psychiatric geneticists have formalized this idea by studying “heritability,” the amount of the variation within a population that can be explained by genetic differences between individuals. Identical twins are more likely to both experience a variety of life events than fraternal twins, who, like siblings of different ages, share only half their genes. About one-fourth of the variation in life experiences — from strictness of parents to difficulties with friends — can be traced to genetic origins
So some of the effects that we call “genetic” (or “nature”) are the indirect result of people being drawn to particular environments because of their personality. Or to put it another way, some “environmental” (or “nurture”) effects are actually attributable to genetic tendencies.
What is often glossed over, even by quantitative geneticists, is that heritability is the proportion of variance explained by a model describing something that is passed from parents to offspring and acts additively. This isn't always genes (although under most situations and experimental conditions it is). We are still interested in heritability because it plays a role in how populations evolve, but we don't have to be tied to the assumption that this will always involve DNA molecules.
photo cc-by kacascade
