The cloakroom attendant was the first person to alert me to the fact that a baby cannot attend a sex exhibition. “Oi, madam,” she cried. “You can’t bring that child in there.” I was en route to Seduced at the Barbican, which I would describe as dirty pictures through the ages, except the organisers want to emphasise that it is, actually, “a comprehensive exploration of the boundaries of exploration in art”.

Anyway, I eluded the attendant but the nice woman in charge of the preview explained apologetically that a ten-month-old baby does indeed fall within the prohibition on anyone under the age of 18 looking round.

“But she can’t be depraved and corrupted,” I pointed out. “I can.” No go. Ten months old is, however you want to look at it, under the age of 18. So I parked the infant, all cosy in her bear suit, next to the reception desk and left her to suck her dummy and contemplate the attendees drinking prosecco and eating oysters (aphrodisiacs, see) while I went round.

It was a minor but suggestive episode. How is it that a baby is barred from an exhibition about sex and the art that is intended to make people want to engage in it? Because a baby is, of course, the natural outcome of sex. It is, from the physiological point of view, the object of the whole exercise. All the exhaustive depictions of the act are designed to encourage you to engage in an activity that nature, in all her brutal utilitarianism, intends to result in a baby. Taking an infant round the show would be tantamount to a rival exhibit – entitled The End Result.

And one of the most basic aspects of pornography is, of course, that it separates cause and effect, sex and procreation. It is hard to imagine anything more detumescent than an infant obtruding on the serious business of titillation. But it’s still ironic when you consider that, until relatively recently, quite the most popular subject was the sexual activity of the gods. I can’t think, offhand, of many heterosexual encounters between gods and girls that were not fruitful.

To take a few of the subjects in the exhibition, Leda and the swan, Danaë and the cloud, Jupiter and Antiope, all resulted in offspring: in poor Antiope’s case, twins. Fecundity is the basic subject matter of mythology – it might be lewd, but it has a point.

Our own porn culture has obviously taken the stuff of antique filth and brought it to the level of the commonplace by making it so accessible. What was once intended for rich men’s bedrooms and public brothels is now yours for under five quid in any newsagent. But the gist is the same – it’s sex without consequences.

Which is why I rather regret the age limit on the exhibition, quite apart from it being based on the rather lovely illusion that under-18-year-olds can be depraved by anything much. An infant in a pushchair would put the whole thing in context.

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