Neither of these explanations need trouble us. We are not going to use cloning to make the whole of the next generation from one individual (though in the 1930s several eminent geneticists thought that when IVF became available, lots of people would rush out to choose prominent men such as Lenin as a father--which just goes to show how wrong geneticists can be about the future). Also, genetic mutations accumulate much too slowly to worry us.

And even if sex proved to be genetically unnecessary, it still wouldn't be a total waste of energy. It is to sex, after all, that we owe most of the things we consider aesthetically appealing in nature. If it were not for sex, there would be no blossoms and no birdsong. A flower-filled meadow resounding with the dawn chorus of songbirds is actually a scene of frenzied sexual competition. Geoffrey Miller, an evolutionary psychologist at University College London, has pointed out that everything extravagant about human life, from poetry to fast cars, is rooted in sexual one-upmanship.

"If women didn't exist, all the money in the world would have no meaning," said Aristotle Onassis, who should know. Or, as Henry Kissinger put it, "power is the great aphrodisiac." So where would humans - and human civilization - be without sex? Probably back with the aphids and dandelions, I suspect, procreating effortlessly but building neither empires nor cathedrals.

Matt Ridley is the author of "The Red Queen: Sex and the Evolution of Human Nature." His newest book, "Genome: The Autobiography of a Species in 23 Chapters," is due out in February

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