Nicholas Day

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__buse, stress, utter indifference__an 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.

We are at the tail end of a decline in infant mortality that began just over a century ago. Babies no longer wander into open hearths or are mauled by marauding pigs. We have vaccines, lead-free educational toys, diapers that can sop up a typhoon. But we have never been more worried.

You'd expect academics, people who are by training comfortable with complexity, to be the most resistant to the idea that we're shaped by any single factor. In fact, they are often the worst offenders. Immersed in their own research, shaped by their own work, many logically see everything else as a natural extension of it.

Over time, parents have barnacled the most routine activities in infancy with their own preoccupations. It's sometimes hard to see the baby for all the barnacles.