[NoImmatureAdHom]

If genes are affecting behavior [I assume you mean variation within the species], then why wouldn't they be relevant? Relevant to what?

I agree culture is the biggie (education is part of culture).

Your example gets at a correlation that can be used to make good predictions. Better-than-chance bets. The example I gave with drug addiction supposes the reader already believes that genes have a causal relationship with drug addiction. That is, a propensity to be, say, an alcoholic can be in your genome and not a result of environmental factors.