The psychologist Jerome Kagan has argued that parenting has a threshold function: up until that threshold is crossed, the effects of a child's very early experience even out in the end. But parenting that crosses the threshold--abuse, stress, utter indifference--can sink in deep, especially if the baby remains in that environment. There's a lot to be said for this perspective on parenthood, not least that it offers well-meaning parents some relief from scaremongering. It also accounts for the astounding flexibility of the human infant: he is game for the craziest parenting stuff you can come up with.