These blurred lines often give rise to nature's most fascinating sexual organs. “There's not a binary that is categorically one thing or the other when it comes to genitalia,” says Willingham. Many of the creatures packing the most surprising phalluses are hermaphrodites, meaning they also have female reproductive organs. Gender and sex rarely fit into tidy categories and animal penises are no different. Typically, a penis helps male animals reproduce sexually with a female-however, exceptions exist. One explanation for this research gap, says Willingham, is “because of who has been asking the questions until quite recently, and who's been deciding how those questions should be answered.” Penises have been a longstanding subject of scientific fascination, and they’re far more studied than vaginas. Phallacy plunges readers into the wild and wacky world of animal genitalia while exploring the social and cultural significance of penises as symbols of power and identity. Her book, Phallacy: Life Lessons from the Animal Penis, hit shelves in September. Just ask Emily Willingham, a biologist and journalist who’s been studying penises for over a decade. The more scientists learn about penises, the more they realize how varied sex organs are. Across vastly different species and ecosystems, unique environmental pressures have allowed creatures of many species to evolve an array of shapes and sizes-from the electric blue penis of the leopard slug to the blue whale’s ten-foot phallus. Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/ have them, bees have them, even regular old fleas have them, but in the animal kingdom, no penis is exactly like the next. “But looking at the reproductive anatomy, we’re learning that they have all sorts of cryptic ways to control paternity.” “It might appear behaviourally that females are very passive,” says Orbach. This combination of precise positioning and complex vaginal structures means that subtle mid-copulation movements by females could send the penis the wrong way in their vaginas, preventing fertilisation. That is consistent with Orbach and Mann’s observations of wild porpoises and dolphins mating. Any deviation from this tended to result in unsuccessful penetration. In all four species studied, the ideal position for successful fertilisation appeared to be the male on top with his penis hooked underneath the female. “She may not choose who she mates with, but might be able to choose which male or, more precisely, which sperm, fertilises her egg.” However, vaginal folds could grant her some agency, says Janet Mann of Georgetown University in Washington DC. When confronted by such an alliance, a female has little choice in who mates with her, and may mate with everyone. Male bottlenose dolphins form alliances two to four strong to keep competitors away from females. But the common porpoise and bottlenose dolphin had extensive vaginal folds that obstructed penis entry. The vaginas of the common dolphin and common seal seemed amenable to penetration, suggesting their genitalia had evolved to allow males access. They also took CT scans of penises inserted into the corresponding vaginas, to determine whether they fitted in easily and the best positions.

They inflated the males’ penises with saline to see how they looked when they were erect, and compared them with the vaginal moulds. Orbach, Brennan and their colleagues obtained genitals from marine mammals that had died of natural causes: common and bottlenose dolphins, common porpoises and common seals. So Orbach wondered if female cetaceans’ unusual vaginas had also evolved to keep out unwanted sperm. Orbach’s collaborator Patricia Brennan of Mount Holyoke College, Massachusetts, has previously found evidence that duck vaginas have evolved to make it harder for males to force copulation. Similarly complex vaginal structures are found in several species of duck. “There’s this unparalleled level of vaginal diversity that we had no idea existed before,” Orbach says.

Dolphin vagina shapes