Orgasms in animals.

From Popular Science:

FYI: Do Animals Have Orgasms?

Well, probably, but how can you tell?

Ah, the age-old question. When animals are going at it like, uh, animals, how does it end? Is there an animal version of the Big O?

It's a bit hard to say, actually. "The short answer is that we don't know much about orgasms in other species -- in fact, scientists are still studying the significance/evolution of female orgasms in humans," Marlene Zuk, a professor of ecology, evolution and behavior at the University of Minnesota, wrote me in an email.

Unlike humans, animals can't tell us they're having orgasms, so we can't truly know what their experience is like. For the most part, we assume that male animals orgasm because there's an ejaculation--though one can happen without the other, they usually go hand-in-hand. (Or something in hand.) The question of female orgasm is, as usual, more hotly contested, though all female mammals have clitorises.

Scientists can infer that animals--mostly primates--orgasm through recording physiological or behavioral aspects, like muscle contractions or changes in vocalization. Studies of primate orgasm have often focused on macaques, a subset of monkeys which are used often in research because they're genetically similar to humans and have similar reproductive systems. According to Alfonso Troisi, a clinical psychiatrist in Rome who has studied female orgasm in Japanese macaques, they're easier to study in the lab than gorillas or chimps. Macaques species tend to have longer copulations than other primate species like gorillas, which is a bonus if you're trying to observe their mating behavior.

"In the lab, by artificial stimulation, it is possible to trigger female orgasm in virtually any primate species."In a 1998 study, he and his co-author wrote that "Under specific circumstances, nonhuman primate females may experience orgasm." But, the rate at which the females orgasmed was variable, and they weren't exactly sure what caused them. Their study found that the level of dominance of the male macaque might play a role, for instance. But, as Troisi wrote me via email, "In the lab, by artificial stimulation, it is possible to trigger female orgasm in virtually any primate species."

Read the rest here.