<p>There are more overt environmental influences, as well. For example, there are good data showing that exposure to lead, even at levels below the threshold considered significant, results in reduction of IQ. Prenatal alcohol exposure is another well-established factor. And it’s hard to believe that nutrition, either prenatally or in early childhood, doesn’t affect brain development. So the idea that IQ (even accounting for differences in tests, norms, constructs, etc.) is entirely genetic is much too simplistic.</p>