Thursday, November 27, 2008

Does paternal investment increase child IQ?

The latest issue of Evolution and Human Behavior has an article on paternal investment and IQ. Using a longitudinal dataset of children born in Britain in 1958, Nettle (2008) found a significant positive correlation between a child’s IQ at age 11 and the father’s degree of family involvement. The less a father cared for his offspring, the less intelligent they were. Nettle concluded that paternal investment affects childhood IQ.

Now, correlation is not causation. It can be shown, for instance, that Presbyterian ministers in Boston have earnings that significantly correlate over time with the price of rum in Havana. But that doesn’t mean they’ve been dabbling in the rum trade. It simply means there’s a common causal factor, in this case the North American business cycle.

Similarly, a common cause may explain the correlation between low investment by fathers and low intelligence in their children. Deadbeat dads tend to be more present-oriented and probably less intelligent. Since intelligence has a large heritable component, their children would be less intelligent on average.

In all fairness, the Nettle study did control for social class, which in turn partially controls for time preference (i.e., whether the fathers were present-oriented or future-oriented). Specifically, the fathers were coded in terms of five occupational categories: professional, managerial and technical, skilled, partly skilled, and unskilled. I doubt, though, that this factor would have accounted for most variability in time preference. Even within the British working class, there is considerable variation, notably by religion and ethnicity, in the respective weighting that people give to present impulses versus future obligations.


Nettle, D. (2008). Why do some dads get more involved than others? Evidence from a large British cohort. Evolution and Human Behavior, 29, 416-423.


Anonymous said...

If a deadbeat dad had spent extra time with his children doing so might not have improved their IQ.

Perhaps his children have less potential improvement from being read to ect. And of course the tendency to have large families might mean the children would be spending time with each other compensating for their lesser share of their fathers total time available.

A high investment dad might be getting a bigger return on his time as the child might have a potential to recieve IQ improvement from paternal association far beyond the low cut off point (where additional parental investment ceased to be cost effective) of the lower class children.

A good way of finding out would be to discover if the children of lower class parents who were given to adoptive parents of the professional/managerial class benefited (inasmuch as they gained IQ points over expectations) more than the children of even one professional/managerial parent* who were adopted into lower class families had their IQs lowered .

I've read that adoption authorities have a policy of placing children of one or more relatively higher socio-economic status parents with adoptive parents of a similarly high SES.

*I don't imagine that many children of two professional class people come up for adoption.

Anonymous said...

As a parent who spent hours reading to his kids, I long ago concluded that their love of reading was due to the genes I passed on to them rather than the reading I did for them.

However, the reading was rewarding.

Anonymous said...

Studies do seem to show that adopted children gain IQ from being brought up in a middle class home. I wonder if the adoption authorities may be able to recognise the more able lower class child at a very early age and prefer to match them with the best homes that are available.

Anonymous said...

The adoption studies I've seen indicate that a middle-class family environment does boost the intellectual performance of adopted children during childhood and adolescence. This effect, however, tends to 'wash out' over time and is usually gone by the end of adolescence.

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