The Roots of Intelligence: The Problems with “Nature vs. Nurture”

The Problems with “Nature vs. Nurture”

Plainly, people differ from one another in their intelligence and their talents. But what causes these differences? This question is often framed in terms of two alternatives— the notion that what matters is genetics and heredity, or the notion that what matters is environment (and so learning and experience). The options, in other words, are boiled down to the dichotomy of “nature vs. nurture.”

As we discussed, however, this framing of the issue makes no sense, because the influences of genes and environment are inevitably intertwined. Specifically, someone’s genetic heritage merely establishes his genotype; the traits he ends up with (his phenotype) depend on how the process of development, guided by that genotype, unfolds. That developmental process is, of course, heavily shaped by genetic factors. But it is also powerfully influenced by the person’s environment—what nutri-ents he’s exposed to, or what toxins; and, crucially, what experiences he has. In short: There’s no such thing as genetic influences independent of environment.

Likewise, how someone benefits from experience depends on her capacity to per-ceive, to understand, and to form memories. And these capacities depend on the biological equipment that each person has—her eyes, for example, and her brain. This biological equipment, in turn, is heavily shaped by the person’s genotype. As a result, there’s no way for experience to influence us independent of genetics.

Even with these points acknowledged, it’s clear that some traits are more directly shaped by genetic influences than others. For example, the color of someone’s eyes (assuming he’s not wearing tinted contact lenses) depends almost entirely on the genetic pattern he has inherited. Conversely, the language that someone speaks (French or Italian, Walbiri or Bantu) depends on where (and with whom) she grows up. As it turns out, to the fact that someone can learn language at all is heavily guided by genetics. But the choice of language depends on the environment, not on genes.

Where does intelligence fall in this range from heavily influenced by genes (like eye color is) to less influenced (like choice of language)? We took some steps toward answering this question earily —and, as we saw there, the answer is complicated: In some circumstances, genetic factors play a large role; in others, genes count for less. And, as we’ll see, the role for genetic influences depends on whether we’re asking why various individuals perform differently on intelligence tests, or whether we’re asking why various groups (racial groups in particular) perform differently on these tests. Let’s start by asking why various individuals seem to have different levels of intelligence.