Sex and the Single Sperm

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By the time Aaron Goetz was in college, times had changed. As a child growing up in San Antonio, Texas, he thought that he might someday want to be a shrink. But on the first day taking a class at the University of Texas at Austin from David Buss, one of Shackelford's own mentors, he knew that evolutionary psychology was for him. "I called my mom and said, 'Mom, I know what I want to be when I grow up,'" he says. "And that was an evolutionary psychologist. It was the integration of evolutionary thinking into human behavior, which made complete sense to me. I mean, how else could it be?"

It made so much sense that he used an EP perspective in his thesis, "Alternative Female Mating Tactics: The Role of the Satellite Female," to study the tactics unattractive women use to pick up men while out with more attractive female friends. He concluded that ugly girls use humor in place of looks. "Perhaps it is no coincidence that most female comedians have unattractive bodies," he suggested.

Goetz came to FAU specifically because of Shackelford. "I knew that sperm competition was the most exciting research going," he says. By 2002, Goetz was on the front lines of evolutionary psychology, researching fake sperm recipes.

Shackelford and Goetz, like all evolutionary psychologists, see sex as a heartless matter of genetic warfare. A winner-takes-all contest where the prize is passing on your genes, it's a battlefield where those with adaptations that help them get laid pass their genes on to future generations.

"We're essentially organic robots," Goetz says. Our behavior, he explains, has nothing to do with what we consciously want — those emotions and desires are just a smoke screen for evolutionary programming. Especially when it comes to sex. "If you think of a penis as a tool," he says, "men might use that tool."

Charles Darwin himself first mapped out the theory of "sexual selection" and devoted the last years of his life to describing it. He came to believe that the competition over mates had as big an effect on evolution as the other environmental influences of natural selection.

It's sexual selection that explains a lion's mane or a peacock's tail — anything, in short, that animals use to attract the opposite sex. And in the 1970s, scientists began to wonder if that kind of competition also took place on the level of sperm.

The term "sperm competition" was coined by biologist Geoffrey Parker, who noted that a male yellow dungfly will sometimes interrupt another male having sex with a female by lifting him off, tossing him away, then immediately taking his place. If both dungflies' sperm were in the female at the same time, Parker reasoned, the male with the faster-swimming sperm would turn out the evolutionary winner.

"That was the announcement of a new type of sexual selection," says Randy Thornhill, a prominent evolutionary psychologist and co-author of the highly controversial 2000 book A Natural History of Rape, which argues that evolution programmed men to rape women when they otherwise couldn't find willing mates.

"[Parker] extended Darwin's earlier work on sexual selection tremendously. He showed that sperm between different males compete... that this was a real evolutionary force in insects."

Once scientists started looking for evidence of sperm competition in animals, they found all sorts of examples. Some species have sperm that actively attack and subdue the sperm of rival males inside the female. Others sport penises with elaborate hooks and curlicues that grab competing sperm out of a vagina. Male birds of some species "guard" their mates to prevent being cuckolded, while others "poach" females to increase the chance of spreading their genes widely. There's even a type of duck that forcibly rapes its mate if it catches her "cheating" on him.

Evolutionary psychologists pounced on the growing body of evidence of sperm competition in animals as a reason to research it in humans. If evolution had programmed birds and insects to rape and guard, they reasoned, it might have programmed humans too.

"There's incredible evidence for sperm competition in birds, fish, and mice," Shackelford says. "There's no reason to believe that humans are the oddball at all."

But the first scientists to apply the theory of sperm competition to humans, a pair of researchers named Robin Baker and Mark Bellis, may have done more harm than good. In 1995, they published Human Sperm Competition, a book that outlined their ideas from several years of research. Disappointed by the lack of reaction to the book, Baker rewrote it for a general audience and called it Sperm Wars.

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Julia Reischel