Whenever I talk about The Nurture Assumption there are a minority of angry and peeved comments. Usually they’re not too coherent, but they don’t get me down. The reality is that the basic message of the book is very important to get out to the American public, by which I mean upper to upper middle class Americans (since these are the target of “think pieces”). The reason is that today the “nurture assumption” reigns ascendant, and makes superhuman demands on parents, especially mothers. This explains some of the reaction to a new paper, Does the Amount of Time Mothers Spend With Children or Adolescents Matter? (ungrated). For a representative example, see in The Washington Post, Making time for kids? Study says quality trumps quantity. Quality as in quality of time.

But one thing bothers me about these treatments in the press: the totally confounded nature of causality. Consider:

The one key instance Milkie and her co-authors found where the quantity of time parents spend does indeed matter is during adolescence: The more time a teen spends engaged with their mother, the fewer instances of delinquent behavior. And the more time teens spend with both their parents together in family time, such as during meals, the less likely they are to abuse drugs and alcohol and engage in other risky or illegal behavior. They also achieve higher math scores.

The implication above is that “time engaged with mother” → “less delinquent behavior.” But we don’t know that that’s causal at all. Rather, it could be a correlation between a third factor, term in “prosociality,” and these two variables. More generally if you look for references to genetics in the original paper you won’t find it. It strikes me that one of the reasons that parental investment doesn’t seem to matter so much is that there are many outcomes they just aren’t effecting, because their primary contribution in heritable, with a major secondary contribution to the environmental context in which children grow up (the “non-shared environment”).

High parental investment also isn’t about the children in the proximate sense (though parents sincerely believe that it matters ultimately). Rather, it’s a form of inter-familial status competition. The “best” parents are those who invest the most, and achieve the best outcomes in their offspring.