NATURE VS. NURTURE, PART 4,578….Are variations in intelligence primarily due to genes or environment? A new study suggests that the answer is: it depends.

Specifically, it depends on how good your environment is in the first place. If you’re middle or upper class, and have a reasonably good environment to begin with, then variations are mostly due to your genes. But if you’re at the bottom end of the lower class, your environment is likely to overwhelm genetic differences:

Specifically, the heritability of IQ at the low end of the wealth spectrum was just 0.10 on a scale of zero to one, while it was 0.72 for families of high socioeconomic status. Conversely, the importance of environmental influences on IQ was four times stronger in the poorest families than in the higher status families.

As sensible as this seems, it turns out this is a new result. And it makes sense: at a certain point, improving your surroundings just doesn’t make much additional difference, which explains the weak effect of environment for a broad swath of middle class and upper class kids. (And it also ought to be a signal to middle class parents not to worry quite so much about Mozart tapes and preschool assignments.) But a really lousy environment, on the other hand, can make a huge difference. Basically, it’s a lot easier to break something than it is to significantly improve it.

If these results hold up ? always something to be cautious about ? they are significant both for their scientific value and for the way they address some very important public policy issues. In other words, don’t let the Bush administration gut the Head Start program just yet. It might actually be making a difference.

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