Dr. Jones: Size matters for IQ

From Slate's Will Saletan:

Twins had IQ's nearly 7 points lower than their nontwin siblings, on average, in an old sample of 10,000 Scottish kids. Family size, mother's age, and father's social class didn't correlate with IQ differences, but gestational age and birth weight did.

The study concludes it's "very likely that there will still be differences in cognition between twins and singletons because of the shorter gestations and impaired fetal growth that affect some twins."

I know that deep down, you really really want to believe that the reason for the lower IQ's among twins is because their parents aren't paying as much attention, since there are two kids rather than one. I understand the feeling---when it comes to IQ, we all become amateur anthropologists, seeking feverishly for any cultural explanation for the large IQ differences that exist between many human groups. But it ain't there, at least not this time 'round.

The link to Slate is here.

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Orig. Posted by Garett Jones at 11/29/2005 09:19:00 PM