Why kids come out that way

I just read something that cast new light on my previous question of whether stigma against single parenting would be good for kids. Scott's summary of a point from Judith Rich Harris's The Nurture Assumption:

"Studies do show that parents who adhere very meticulously to the standard parenting advice have children who, let's say, do better at school. But Harris points out - what personality trait is necessary to adhere meticulously to the latest parenting fads? Conscientiousness. What personality trait is necessary to do well at school? Conscientiousness. And what personality trait is about 50% heritable (recall that most things are about 50% heritable)? Conscientiousness. So the discovery that parents who adhere to parenting advice have children who adhere to school rules is absolutely worthless until you control for conscientiousness - after which the finding should disappear. . . .

Harris thinks that these sorts of problem explain the much-trumpeted findings that kids from single-parent homes and children of divorce tend to turn out worse. After all, what kind of fathers abandon their partners and young children? Low conscientiousness fathers who probably have a lot of personal issues. So what kind of children would we expect them to have, just by genetics alone? Low conscientiousness children who probably have a lot of personal issues. And surprise! Children of single parent homes are low conscientiousness and have lots of personal issues! But - and here's something I had never read before - this is true only of homes that are single parent because the father left. If the father died - in a car accident, of cancer, whatever - those children turn out exactly as well as children of double-parent homes! Exactly what one would expect if the problem were caused by what the split implied about genetics and social situation rather than by the parenting itself."

I'm always pleased to find evidence that I don't have to be a frantic parent.