Porn Helps Human Sperm Gear Up for Competition

Animals have developed some fascinating tactics to ensure that their genes survive to the next generation: impressive color displays, the best pheromone smell, sperm that induces the female to ovulate right after mating. And humans apparently aren’t above such biochemical shenanigans.
A recent study has shown that human sperm are honed for competition.

The study, conducted at the University of Western Australia, examined the effect of gender-specific pornography on sperm. On one day of the study, the heterosexual subjects donated samples while they viewed pornography that featured three women. On a separate day, the same subjects viewed X-rated pictures depicting a woman with two men. Overall, the sperm became more vigorous—and, it’s surmised, more fertile—after the subjects watched other men in action. “We found that men viewing images containing both men and women had higher sperm motility in masturbatory ejaculate,” explained the head researcher, Leigh Simmons.

But why does heterosexual sperm key up around sexy men? Simmons thinks it has something to do with sperm competition. Deep in our species’s past, a particular female often had multiple male suitors at one time. As a result, an assortment of sperm swarmed toward her ova, and the fastest swimmer won the fertilization contest. Over time, the researchers surmise, human males evolved to rev their sperm when they faced this kind of competition. So as the study subjects watched other men have sex, the perceived challenge worked their sperm into a frenzy.

It’s not surprising that science has confirmed that we’re not so different from our animal brethren. Most other animals have sperm that roils near competitors too, but the race to the egg isn’t just about speed—it’s also about cheating. The dragonfly, for example, has a bristled, scoop-shaped penis. He uses it to brush foreign semen away from his mate’s egg, giving his own swimmers
a head start. The chimp cheats later in the game. He kills offspring fathered by other chimps and then plants his seed before the bereaved female finds another mate. Even the lowly sea squirt preemptively swindles other would-be fathers. The rock-bound sea squirt casts his sperm into the water, sterilizing
other, competing species’ ova. With fewer unrelated spawn cruising the waters near his permanent home, the sea squirt can hoard his real estate for his own offspring.

These tactics may seem a bit dodgy, but people shouldn’t get too smug. Even if our sperm don’t cheat on their way to the egg, some humans still practice the disturbing habit of buying pheromone perfume over the Internet.