Sex Differences in Sexual Choosiness
Women are choosier about their mates than men... but not always
This is the latest excerpt from my forthcoming book A Billion Years of Sex Differences. You can access the full collection here, and preorder the book here (UK) or here (US).
In this installment, I share one of my favorite sections of the book, which explores one of the deepest patterns in nature: greater female choosiness about sexual partners. Among other things, we’ll look at:
Why men dominate what biologists call “mate-choice failure”
Why women swipe right less
Why some female animals would rather fake their own deaths than mate
Why even female plants are choosy about their sexual partners
Why men are less choosy in casual mating but not in long-term relationships
Why female orgasm may be choosier than male orgasm
Women Are Choosier than Men About Their Mates… But Not Always
Woman is the dominant sex. Men have to do all sorts of stuff to prove that they are worthy of woman’s attention.
–Camille Paglia (attributed)
Aside from sexual orientation, the most fundamental sex difference in mate choice concerns overall sexual choosiness. The evolutionary rationale for this difference is straightforward. Both sexes evolve to be choosy in proportion to their level of parental investment. If females and males in a species invest equally in the young, the sexes evolve to be equally choosy. Conversely, if one sex invests more than the other, the higher-investing sex evolves to be choosier than the lower-investing sex. As we know from earlier excerpts, in most species, females invest more than males in each offspring. Ergo, females in most species are choosier about their mates.
Even a cursory glance at the living world confirms the accuracy of this claim. A common trend among animals is that males do everything within their power to impress females, only for the females to remain entirely unimpressed, nine times out of ten. A nice example concerns the greater superb bird of paradise. Males in this species perform one of the most elaborate and bizarre courtship dances known to modern science; google it if you want to feel insecure about your own dance moves. Despite the male’s strenuous efforts, however, females typically reject several dozen suitors before finally consenting to mate. The funny thing is that because females evolved to be so super-choosy about the males’ displays, we humans are probably more impressed by the superb male’s dance than is the average female of his own species. Ditto the peacock’s tail and every other nonhuman mating display.
Greater female choosiness doesn’t just explain males’ desperate attempts to wow the ladies; it explains all sorts of otherwise mysterious behaviour found across the animal world. In some frog species, females fake their own deaths to escape unwanted male attention; males, on the other hand, never fake theirs to escape female attention. In some spiders, females attempt to eat any male that tries their luck with them, thus filtering out suitors that don’t have the skills to avoid becoming dinner. And in some octopus species, females throw shells and other objects at amorous males who they don’t feel measure up. Even apparent exceptions to the choosy-female rule generally turn out not to be. We saw in a previous excerpt that female chimps and bonobos are highly promiscuous, commonly mating with every adult male in the group. Importantly, though, underneath this stereotypically male behaviour is a strong undercurrent of stereotypically female choosiness. The females’ sexual adventurousness, you see, is largely confined to the period leading up to estrous – that is, the period before they’re fertile. As soon as estrous kicks in, the females become much more socially conservative, reserving their sexual favours for the highest status males.
And we’re still only scratching the surface! Female choosiness isn’t just a behavioural phenomenon; it’s often stamped into female anatomy and physiology. Some female ducks, for instance, have corkscrew vaginas that spiral in the opposite direction to the males’ corkscrew penises, helping them to avoid fertilization by rapist males. In some species, including some rodents and sea urchins, eggs are choosy about which sperm they allow to fertilize them. And in some plants, female reproductive organs are choosy about which pollen they accept, selectively aborting ovules fertilized by suboptimal pollen. Yep, that’s right; greater female choosiness isn’t even confined to animals. It’s an extremely deep trend in nature.