Skip to content
Who's in the Video
Richard O. Prum is an evolutionary ornithologist with broad interests in avian biology. He is the William Robertson Coe Professor of Ornithology at Yale University, and the Head Curator of[…]

Duck mating—for what it’s worth—is a surprisingly complex issue with one hand (webbed foot?) in the #MeToo movement. Really. Richard O. Prum, Head Curator of Vertebrate Zoology at the Peabody Museum of Natural History at Yale University, has a lot to say about the matter. Did you know that male ducks often force sex on female ducks that aren’t their mates, to the point where female ducks’ genitalia has evolved to try and counteract what biologists have politely termed “forced copulation”? The lady ducks have found a way to shut out sexual predators. In other words: the power of the female’s choice has literally advanced the species. Ultimately, Prum says, patriarchy is about “coercive control over female reproductive autonomy, whereas feminism is really an ideology of freedom of choice.” Richard’s latest book is The Evolution of Beauty: How Darwin’s Forgotten Theory of Mate Choice Shapes the Animal World – and Us.

Richard Prum: According to aesthetic evolution, animals are agents in their own evolution; that is, through their choices they end up shaping their own species.

One of the implications of this idea is a new perspective on what happens when mate choice is infringed or violated by sexual violence or by coercion in animal species.

One prominent example of this, from our own research, is on duck sex.

Ducks are unusual among birds in having both a typical mate choice situation—where male and females pair up on the basis of display and preferences—and simultaneously other individuals that force copulations on female ducks as they approach reproduction.

So what that means is that as the eggs are being laid, females have to defend themselves from forced copulations by males. Now “forced copulation” is the word that biologists use now, but for over a century biologists used the word “rape” in biology.

Now that was abandoned back in the 1970s in response to the feminist movement and Susan Brownmiller and her work Against Our Will, proposing and articulating a specifically social context for rape in humans.

This led to the creation of a euphemism, “forced copulation,” in biology.

Unfortunately, articulating sexual violence in the animal world with these euphemistic terms has led to scientists losing track of the fact that forced copulation is against the will of the ducks.

And by taking the aesthetic perspective and trying to understand what it is that individual females—in this case ducks—want we have arrived at a new perspective on what it means when they don’t get what they want. So in some ways using socially sensitive euphemisms has led to imprecision or fuzziness in the science.

In the case of duck sex what we find is that males can force themselves on females because they’re among the few birds that still have a penis. And what we find in ducks is, as a result of female resistance and male sexual violence, we find a co-evolutionary arms race between male capacity to force and female resistance.

In this case it takes place in the form of a genital arms race: the males evolve more elaborate and more elaborately armed penises, and the females evolve convoluted vaginal morphologies that exclude the penis during forced population.

So among the many weird things of duck penises is that they’re counter-clockwise coiled. Well, the female vagina (in ducks that have high rates of resistance) actually coils in the opposite direction, so they have literally evolved an “anti-screw” device in their vaginal tract that obstructs the intromission of the penis during forced copulation.

What that means is that what that tea party Senate candidate Todd Akin from Missouri said about women “have a way of shutting that whole thing down” in reference to rape is actually true of ducks. 

But in a way that exposes something fundamentally new and interesting about evolutionary biology, which is that sexual autonomy matters to animals.

Freedom of choice is not merely a political concept discovered by suffragettes and feminists in the 19th and 20th centuries, but is actually an evolved feature of the social and sexual lives of other species, especially in ducks.

How does this work? Well if the female mates with the male she prefers, that is she gets the green head and the “quack, quack, quack,” that she likes, and then her male offspring will share those traits and be sexually preferred by other female ducks who have coevolved those same aesthetic preferences.

But if she’s forcibly fertilized, then her male offspring will either inherit a random trait or one that she specifically rejected, which means that her offspring will be less attractive to other females.

So anything the female duck can do to prevent forced fertilization, through physical resistance or behavior, will evolve because she will be rewarded with more grandkids.

So what this means is that aesthetic norms, the shared ideas about what is beautiful among ducks, gives female ducks the evolutionary leverage to advance their freedom of choice in the environment of persistent sexual coercion and sexual violence. This is really stunning.

In fact we know these ducks are so successful, because in species where 40 or 50 percent of the copulations are forced only two to five percent of the eggs in the nest are fathered by males who are not the social partner.

What that means is that females have a 98 percent successful birth control device that is behaviorably deployable in the vaginal tract in response to sexual violence. That’s like FDA approvable.

And what that shows is the power of female choice to advance the sexual autonomy of individual females.

One of the interesting things we learned from examining sexual conflict in ducks is that the genital arms race between males and females is not really a fair fight. In fact the advances in male coercive capacity are really about control over female outcomes. They are about controlling—physically controlling—fertilization.

However, the countermeasures that females evolve are not actually about power or control, they merely reestablish the freedom of choice, if you will the flat playing field in which individuals are free to choose who they like.

Now this sexual autonomy is not actually about control or control over other individual’s sexual outcomes. That’s fascinating because this asymmetry between male coercion and female resistance in duck sex has really fascinating parallels to a patriarchy and feminism in cultures today.

So for example, patriarchy is historically—and even in a modern sense—about coercive control over female reproductive autonomy, whereas feminism is really an ideology of freedom of choice.

So that same symmetry between male power and freedom of choice is elaborate and present today.  And we can see this explicitly because patriarchy and men’s rights and “incel” movements all articulate feminism as a countervailing force of control over male reproductive outcomes, but that’s a fantasy. In fact sexual autonomy includes the freedom to be rejected, which is a lesson that we learn from duck sex.