No Two Alike: Human Nature

William Saletan writes:

Judith Rich Harris calls "No Two Alike" a "scientific detective story." The mystery is why people -- even identical twins who grow up in the same home with the same genes -- end up with different personalities. ...

Eight years ago, Harris's book "The Nurture Assumption" set academic psychology on fire by attacking the notion that parenting styles shape children. ...

Harris shreds popular theories of personality formation. Does home environment -- parenting style, marital harmony, the use or rejection of day care -- shape a child's personality, making her more agreeable, less aggressive or more extroverted? Nope. Research shows that twins don't turn out more alike if they're raised together than if they're raised apart. Nor do adoptive siblings. And when you compare apples to apples -- making sure that each parent-child unit in a study is as genetically related as any other -- being raised in one home rather than another, on average, makes no difference.

This is one of those subjects where people cling to their beliefs, regardless of the evidence.