Poverty, Biology, and Intelligence

Science, technology, and life.
April 7 2009 10:28 AM

Poverty, Biology, and Intelligence

Why do poor kids have more trouble in school? Is it due to environment or biology?

The answer, according to a new study, may be both.

William Saletan William Saletan

Will Saletan writes about politics, science, technology, and other stuff for Slate. He’s the author of Bearing Right.

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We tend to think of biological explanations as an alternative to environmental explanations. The clearest example of this conflict is the debate over genetic theories of intelligence . But biology is more than genetics. It includes physical processes that are environmentally influenced. So if poverty causes cognitive impairment, biology should be able to explain part of the effect.

That's what a study published last week in Proceedings of the National Academy of Sciences tries to do. Working with a sample of nearly 200 children, the authors set out to identify "underlying biological mechanisms that may account for the income-achievement gap." But instead of looking for genes, they look for a different kind of mechanism: measurable stress.

And they find it. "Childhood poverty no longer predicts young adults' working memory capacity once chronic stress exposure is partialed from the covariance between childhood poverty and adult working memory," they report. In other words, stress is the missing link. They conclude:

One, we demonstrate that the duration of childhood poverty is related prospectively to working memory performance later in life among young adults. Two, we show that allostatic load, an index of chronic stress, conveys a significant proportion of the covariation between childhood deprivation and an adult's working memory performance. The longer the period of childhood poverty, the higher the levels of allostatic load during childhood, and the greater the reductions in young adults' subsequent working memory. Furthermore, elevated childhood allostatic load predicts working memory in young adults and, in turn, largely explains the prospective relationship between childhood poverty and these working memory deficits.

In an interview with Rob Stein of the Washington Post , the study's lead author enumerates various ways in which poverty can cause stress: "You may have housing problems. You may have more conflict in the family. There's a lot more pressure in paying the bills. You'll probably end up moving more often."

This study alone doesn't settle anything. It hasn't monitored cognitive performance over time, doesn't measure performance beyond working memory, and doesn't rule out other underlying factors. But it shows how biological and environmental explanations can help each other. And that's an important lesson in a field too often polarized between the two.