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painting of amourous coupleessay: The Advantage of Sex by Matt Ridley

Why does sex -- that is, sexual reproduction -- exist? In many ways, asexual reproduction is a better evolutionary strategy: Only one parent is required, and all of that parent's genes are passed on to its progeny. In sexual reproduction, only half of each parent's genes are passed to the next generation. What's more, a mate must be found. Yet sex persists.

This essay offers possible explanations of this evolutionary paradox.

Matt Ridley is the author of The Red Queen: Sex and the Evolution of Human Nature (1995), The Origins of Virtue: Human Instincts and the Evolution of Cooperation (1998), and Genome: The Autobiography of a Species in 23 Chapters (2000). A former science editor and Washington correspondent of The Economist, he now lives in northeast England, where he is chairman of a science center called The International Centre for Life.

Adapted with permission from New Scientist, 4 December 1993, no. 1902 © 1993 by RBI. (Boldface added.)

painting of amourous couple
human style

A variety of theories have been proposed over the years to explain why sexual reproduction may be more advantageous than asexual reproduction, and, for that matter, why sexual reproduction even exists at all. For years everyone accepted the general proposition that sex is good for evolution because it creates genetic variety, which, in turn, is useful in adapting to constantly changing and challenging environments. But it may give organisms a very different kind of edge.

By the late 1980s, in the contest to explain sex, only two hypotheses remained in contention.


One, the deleterious mutation hypothesis, was the idea that sex exists to purge a species of damaging genetic mutations; Alexey Kondrashov, now at the National Center for Biotechnology Information, has been its principal champion. He argues that in an asexual population, every time a creature dies because of a mutation, that mutation dies with it. In a sexual population, some of the creatures born have lots of mutations and some have few. If the ones with lots of mutations die, then sex purges the species of mutations. Since most mutations are harmful, this gives sex a great advantage. black salamander
Salamanders can
reproduce sexually
or asexually.
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