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The Straight Dope

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The other day we were thinking about sex. Not much new there, you may think. But this time we got to wondering how this charming custom got started. How did a little sexless critter split into two new critters, one with an archeolingam, the other a protoyoni? [Primeval reproductive apparatus, for you rustics. --C.A.] Wonderful new body bits, and a new type of cell division, getting up and running to do the nasty in a single generation seems like an awful long shot to us. We need some help with this one, Cecil. --Mike Assels, Adam Steele, Montreal, Canada

I'll say. Unfortunately, you're not going to get much from the world of science, which is not only stumped by how sex got started, but is equally adrift on why we keep doing it. Well, you may say, it beats watching TV. But the truth is that sex is not a very efficient means of reproduction. Not to be crude about it, but we've all had evenings where a sizable investment in flowers, lamb chops, and after-shave netted us nothing but a handshake. More to the point, asexual reproduction, such as that engaged in by our parents, dispenses with men, who, if we look at the matter dispassionately, are a waste of biological material. More than one woman has had occasion to think this, of course, and with good reason. What good is a man? He sits around the house, burping, scratching, and eating all the potato chips, and when it comes to reproduction, where is he? Five minutes to do his dirty business and off to bowling. In the same time a sexual woman can produce a male and a female offspring, your, how shall I say, self-gratifying female can produce two little females, that is to say, two little reproductive engines, and thereby propagate the species twice (at least) as fast.

Sure, sex has its advantages. It is difficult to imagine how the deodorant industry would have amounted to anything without it. But some more fundamental mechanism must surely be at work. A few hypotheses:

Sex is a disease. Dreamed up by someone who had a rough night, no question. But perhaps true. Carl Sagan in his book Shadows of Forgotten Ancestors says, "Perhaps sex started out as an infection, becoming later institutionalized by the infecting and infected cells." This follows a discussion of "how viruses exchange genetic material with their hosts, thus causing major changes in DNA impossible by the slow random mutation process," one of Cecil's correspondents summarizes. Just like sex, notes another, but without the squeaky bedsprings. Sagan also offers the disquieting thought that the invention of sex coincided with the advent of death. Presex, cells simply divided and for practical purposes were immortal. Then again, bacteria do "conjugate," which is vaguely akin to sex (you know, amo, amas, amat), so we dasn't take this sex/death thing too far. A related theory is:

Sex evolved as a mechanism of DNA repair. Harris Bernstein et al (1981) propose that DNA in the early days (and maybe still) was easily damaged, and when sex occurred and two strands combined, you had an opportunity to throw out the bad parts and recombine the rest into one sturdy genetic whole.

Fine, but what keeps the ball rolling? We turn to a seminal article, you should pardon the expression, by Alexey Kondrashov, which begins: "Sexual reproduction--the alternation of meiosis and syngamy with attendant segregation and recombination--is one of nature's wonders." Alexey, you old romantic, one thinks. But who among us, seeing an attractive member of the species, has not thought: jeez, would you get a load of the gametes on that polar body? Anyway, Kondrashov's idea is that deleterious mutations are accumulating in the human population, an idea that an evening at a Knicks game will certainly confirm, and that (I omit a good deal of mathematical subtlety here) sex tends to counteract this. A comforting thought, although probably not one that Ed Meese would have endorsed. We haven't even touched on the intriguing ideas of W.D. Hamilton, nor have we answered the question of how all this evolved in one generation, except to say that it undoubtedly didn't. You're focusing on thrusting loins, whereas the real issue is recombining nucleic acids. Try to keep this in mind on your next blind date.

Art accompanying story in printed newspaper (not available in this archive): illustration/Slug Signorino.

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