Thursday, August 2, 2007

Fertility and the IQ of Nations


We have long known that economic growth was associated with decreasing family size. It appears the increases in IQ may also be associated with decreases in family size. The myriad of ways in which this trivariate correlation could be explained are tantalizing but for now I will leave you with the data itself.



P.S.

I can't help but mentioned that if low IQ caused larger families then we would expect IQs to decline over time. In fact they have been doing the opposite. What I wouldn't give for good measures of Chinese IQ before the 1-child policy.

22 comments:

dWj said...

There are two approaches, at least in the simplistic world of such dichotomies, to successful propogation of one's genes: one either has millions of kids, hoping dumb luck will see a couple of them through to sexual maturity, or one has a few kids and nurtures the hell out of them. I knew a large family once that was clearly trying the first approach, but in industrialized nations the second approach seems to be more in vogue, and it may be that one strategy is more likely to succeed in some institutional environments and the other in others.

(Do you know anything about eusocial animals? If you're interested in evolution -- and what economist isn't? -- eusociality is fascinating not least for the way it clarifies some things about evolution that often trip up laymen.)

Karl Smith said...

I love evolutionary explanations but I wonder if evolution alone can do it here.

The problem is that in the modern world almost all children survive to reproduce. This means that evolution should be driven by fertility.

This would indicate that we are evolving to be less intelligent. And yes, it would evolution not devolution or some other phrase. High intelligence is at least currently an impediment to evolutionary fitness.

The problem with this, however, is the phenotypically IQ is increasing.

So either environmental pressures are swamping evolutionary pressures or the evolutionary pressures are weak.

One possible answers is that smaller families cause higher intelligence. Smaller families in the Western World mean that kids spend a larger fraction of their time in the "adult" world which may encourage brain development.

Perhaps, more straightforwardly smaller families mean more resources per child and less chance of malnutrition, etc.

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