this was in the Philadelphia Inquirer... Carnal Knowledge | Upending ideas on the 'sluts' of the world By Faye Flam The word slut is rarely applied to men. For them the equivalent term might be stud, or lucky guy. Conventional wisdom has long held that male creatures are wired to sleep around while females are supposed to desire nothing more than to tie down one male for life. Now, evolutionary biology is bursting that bubble for animals and perhaps people, too. The latest research suggests the mechanics of sexual intercourse and the shape of the human penis evolved as a countermeasure to the infidelity of our female forebears. Men may not be aware of it, but during sex they may be instinctively using their penises as "sperm displacement devices," says evolutionary psychologist Todd Shackelford of Florida Atlantic University. Biologists have known for years this kind of thing happens in animals, says Shackelford. "It's only shocking when applied to humans." The evolutionary advantage of male sluttishness is obvious - it spreads your genes around. But evolution also may favor females who cheat. Often such behavior helps her beget offspring with better genes. That in turn creates a pressure unique to males: the threat of cuckoldry - evolutionary doom. He who fails to impregnate his mate or who inadvertently brings up another's brood won't pass on his genes. For very promiscuous species such as chimpanzees, the best defense is often a high sperm count, which may explain why chimp testicles are nearly twice the size of a human's. Other male animals compete by developing the ability to scrape or pull out sperm from rivals. The penises of some creatures sport "spikes and knobs and bristles and are often twisted into weird and sinister shapes," writes biologist Olivia Judson in Dr. Tatiana's Sex Advice to All Creation. When the male honeybee, on the other hand, mates with a queen, he leaves his penis stuck inside her, blocking entry for anyone else. The rest of his body explodes. Male rats engage in a safer version of this by leaving a "plug" to prevent other sperm from entering the female's reproductive tract. Once that evolved, other male rats developed the ability to use their penises like plungers to remove the "plug" left by the rat who was there before. In the early 1990s, biologists Robin Baker and Mark Bellis suggested humans evolved from a plug-leaving ancestor, and this explains all that thrusting that goes on. "The repetitive motion was not designed to bring about female pleasure," they wrote. "It was intended to remove a competitor's soft plug and now functions as a piston-like pull-push-scrub-scrape mechanism." Other enterprising scientists used plastic models of human sex organs to see if the old pull-push-scrub-scrape really works to clean out leftover sperm. Apparently it does. Building on all this, Shackelford set out to see if men released more sperm when they sensed competition. Using condoms to collect samples, he found the longer a man's partner had been away, the higher his sperm count. Beyond that, men in Shackelford's study reported they found their partners more desirable and "thrust more vigorously" the longer their partners had been out of their sight. These ideas have not become universally accepted in the scientific community but they may prove the best explanation for the mechanics of sex anyone has offered so far. Better established is the notion of sexual jealousy as a defense against cuckoldry. Male sexual jealousy may explain the pervasive stigma against female promiscuity. The hurtful word slut gets aimed at women not because playing the field is so abnormal but because it can trigger an instinctive rage in men. It's possible the female sluts of the world have had a rough time of it since the paleolithic. But if these new ideas turn out to be true, we owe them credit for making our sex lives what they are today.
