(Inside Science) -- Female dolphins, like human women, are blessed with sensitive clitorises that engorge with blood, according to a new study. But unlike the human version, a dolphin's clitoris appears perfectly placed for stimulation during intercourse. The research is still in progress, with preliminary findings presented today at the 2019 Experimental Biology Meeting in Orlando, Florida.
The researchers studied 12 bottlenose dolphins that were found already dead on U.S. beaches. Patricia Brennan and Dara Orbach, both biologists at Mt. Holyoke College in South Hadley, Massachusetts, dissected the dolphins’ clitorises to determine their overall structure and composition. They gleaned more details by examining preserved slices of the tissue under a microscope. Finally, they scanned tissue samples using a 3-D X-ray imaging technique called micro-CT.
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The first thing that struck the researchers was how large the clitorises were, said Brennan. The shape was similar to that of a human clitoris, although the dolphins lacked structures called vestibular bulbs that extend down on either side of a woman's vulva. Like human clitorises, the dolphin clitorises were composed largely of erectile tissue, dense with blood vessels that would allow them to swell. They were also packed with nerve endings, indicating that the organs were highly sensitive, said Brennan.
The location, though, is different between the two species. The tip of a dolphin's clitoris is located lower than a woman's, right at the dolphin's vaginal opening. "So essentially, there is no way that the copulation could happen [in dolphins] without stimulation of the clitoris," said Brennan.
Sexual pleasure in animals has not received a great deal of attention from researchers, said Brennan. But many vertebrates have clitorises, and rats and some primates are known to experience orgasms. Moreover, dolphins are known to be highly sexual creatures. Males have been seen masturbating and even penetrating each other's blowholes.
Male dolphins often appear to coerce females into sex, and it can be hard to tell what a female really wants in a mating situation, said Orbach. But even though the females are only fertile for a few days every two to three years, they mate year-round, suggesting that dolphin intercourse serves other purposes in addition to procreation.
Of course, one can't prove that an animal experiences pleasure just by examining its anatomy. But it would be hard to measure direct signs of orgasm in a dolphin -- for one thing, they don't have any toes to curl, said Brennan. She argues that unless contrary evidence emerges, it makes sense to assume that dolphin clitorises work the way we would imagine.
"They're probably functioning in providing some kind of pleasure to the female dolphin," said Brennan.