4 surprising facts about sex in the animal kingdom

“So have you heard about the sea slugs that inseminate each other hypodermically in the head?” asks Dr Emily Willingham in her latest book, Phallacy: Life Lessons from the Animal Penis. It’s the kind of question you’d expect from someone who spent five years studying the reproductive systems of red-eared slider turtles.

The fields of evolutionary psychology, genitalia research and entomology (that’s the study of insects) are filled with fascinating information about how frogs, fleas and ducks do it. Until recently, however, these fields have been dominated by men, which has resulted in an excessive focus on penises and left, as biology professor Patricia Brennan put it, the female side of things “a copulatory black box.”

But now, women scientists like Brennan and Willingham are addressing the previous biases, blindspots and outright misogyny of these fields. Unlike their predecessors, they are careful not to let their own anxieties, human experiences and cultural attitudes colour their perspectives. Nonetheless, Willingham’s guide through the specialised and mind-blowing world of animal penises sheds a lot of light the psychology, biology and culture of sex when it comes to our very own species.

Brace yourself for geeky weirdness.

Bird expert and lecturer at the University of Washington, Kaeli Swift, once described duck penises as “sperm-shooting ballistic missiles.” They are long, corkscrew-shaped and ejaculate in less than a third of a second. As you’d expect with such an organ, duck mating is characterised by sexual aggressiveness.

There are many species in the animal world like ducks, which exhibit weaponised penises and forced copulation. However, animals are less likely to exhibit stabby, hard, or crowbar-like abilities if they display a sensory-rich approach to sex.

“The human penis couldn’t stab through a perfectly ripe avocado,” writes Willingham. Similarly, the vagina has no tough barriers that require forceful entry. Our genitalia, in the context of the animal kingdom, does not support the idea that rape is part of human nature.

We tend to think of males as having penises, which are inserted into females for fertilisation. A delve into the world of animal genitalia demonstrates that nature is far more complex. On the island of Vanuatu in the South Pacific Ocean, a breed of pigs are considered sacred because many of them display intersex features, from ovaries to ovotestes (tissues of both ovaries and testes), large clitorises and uteruses.

Likewise, some moles and bears also show mixes of genitalia that we often associate with either males or females. In some species of cave insects and beetles, the female actually penetrates the male with a penis-like organ in order to suck up male sex cells. 

Studies of communities in the Dominican Republic have shown that some human cultures celebrate and accept people who are non-binary, and that this contributes to the psychological well-being of intersex individuals.

Perhaps it is because the clitoris is smaller than the penis, and emanates from the same place during embryonic development in humans, that it is often seen as a lesser penis. However, even in animals such as the hyena, which has a famously long clitoris that the females even give birth through, it is still not celebrated as its own organ.

Scientists frequently refer to it using terms such as “large clitoral pseudopenis.” Female moles, which display impressive external genitalia, have been subject to similar treatment, with researchers referring to their bits as “peniform clitorises.”

The practise of placing the utmost importance on penises, while treating female genitalia as secondary, permeates much of science, and seeps into our sex lives. With the clitoris so undervalued and overlooked, is it any wonder that women orgasm only 62 per cent of the time compared to 85 per cent of men during heterosexual sex?

Let’s go back to the ducks. Duck penises have been the subject of fascination for decades, but what about duck vaginas? When Patricia Brennan went to the University of Sheffield to learn how to dissect genitalia in birds, she saw that the work only focused on male genitalia. Surely, with duck penises being so antagonistic, it would be interesting to see what role vaginas played?

She seems to have been the only scientist interested in investigating the question, and strode out to a nearby farm to acquire a duck that was already doomed for the dinner table to find out. What she found was that duck vaginas were not just passive vessels designed to receive ejaculate; they were equally antagonistic structures, with dead end pockets and a twisting tunnel that ran counter to the corkscrew motion of duck penises. Not only were duck vaginas not passive—they also shaped and influenced the evolution of the male organ.

In a broader context, men are often seen as advancing humanity, while women are seen as passive. Just look at all those depictions of cavemen, standing erect, spear in hand, while women and children huddle on the floor around him. Loretta A Cormier and Sharyn R Jones set this story straight in The Domesticated Penis: How Womanhood Has Shaped Manhood, writing that “Female selection is not an alternate view of evolution—it is integral to evolution.”

A stroll through the field of genitalia research highlights just how culturally loaded sex is—even a supposedly objective discipline like science is tainted by cultural attitudes! However, as scientists like Willingham demonstrates, taking a step back to consider our assumptions, biases and hang-ups about the subject can be a mind-blowing, sexy experience.

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