TAKING CONSTRUCTIVISM TOO FAR? John Ray recommends a Paul Sheehan column in the Sydney Morning Herald that weighs in on parental leave. The opening paragraphs, however, are the most interesting part.

It's time someone praised and defended reckless teenage girls and young women who behave badly, dress provocatively, engage in risky sex, and get pregnant. They are the normal ones. The rest of us are the deviants. They are behaving in the most natural way. The rest of us are mutants.

There is nothing wrong with pelvic display, push-up bras, Gosford miniskirts, spray-on jeans, low-cut tops, bare legs, bare arms, bare ankles, G-strings or even buttock cleavage, providing the displayer is young enough to get away with it. A woman's body is at its fertility peak between the ages of 17 and 23. So when young women advertise or flaunt their sexuality they are being driven by a force far stronger than the Judeo-Christian ethic. They are driven by the power of peak fertility and a million years of evolutionary biology. Nature has programmed them for pregnancy, genetic diversity and keeping the species going. A big job.

Sexually active teenage girls, and sexually promiscuous women of any age, carry the greatest social burden of judgements, punishments, restrictions and risks because we haven't got the child-care equation right. These women are just doing their job. They are real, while the rest of the equation is artificial. Society is the collective weight of traditions, conventions, laws, habits, fears, tribes, taboos and technologies, permeated by a Judeo-Christian ethic dominated by men and designed to curb female sexual power. Our norms are also dominated by the ideology of materialism that is moving women further and further towards unnatural behaviour, pressuring them to have babies later rather than sooner.

This is society's real problem. Teenage pregnancy is trivial by comparison to suppressed pregnancy.

Really? Where did that "nature" get us? There's a reason schools teach Romeo and Juliet to eighth and ninth graders. The protagonists are about the same age as the readers. Why a teenage romance with such weighty content? Because that same nature Mr Sheehan celebrates endowed us with high infant mortality rates, as well as high rates of women dying in childbirth. (There might have been reason for men and women alike to restrict their lovemaking if the consequence of the act was death in nine months for one participant.) So fast-forward 700 years and consider West Side Story. Although the setting of the story is now the poorer quarters of New York, the protagonists now enjoy a standard of living that is opulent by 13th century Veronese standards, although shabby by Central Park West standards. And what is the lot of the residents of the poorer quarters where the women are defying the "collective weight of traditions?" Yup. Higher rates of infant mortality and social disease.

Granted, my biases as economist and curmudgeon are showing. But I must protest in the strongest possible terms Mr Sheehan's characterization of a "tension between fertility and materialism." It is the materialism that makes freer expressions of sexuality possible, by obtaining the means to prevent or terminate pregnancies or to understand and cope with the complications of childbirth. Nature, on the other hand, responds to the successes of materialism by accelerating puberty. And that's totally logical. A living thing that has an easier time maintaining itself develops more quickly the ability to reproduce itself. Any gardener worth his Miracle-Gro is exploiting that tendency. But harvesting a tomato early is a very different proposition from preparing a nine year old -- or a nineteen year old -- to raise a baby, precisely because mastering materialism takes a lot of thought and preparation. As well as making it possible for thirty- and forty-somethings to have babies.