Facts So Romantic

A Huge Outdoor Orgy Is Beginning; Humans Not Invited

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When the cicadas of Brood II burst into open air—and into song—later this month, after living 17 years in darkness below ground, they will have one thing on their collective, eerily synchronized mind: sex. Though millions of humans inhabiting the mid-Atlantic states will soon hear the insects’ incredible racket, they’re probably unaware that what they’re hearing is an enormous mating festival.

These particular insects have been underground—where the sexually immature nymphs dig around, suck on tree roots, and bide their time—since 1996. This is their coming-out party, their debutante ball, and we all get to be a part of it, whether we decide to make ice cream out of them, fry them into tasty little bug nuggets, or just sit out on the porch in their deafening hum, pondering the peculiarities of other species’ reproductive habits.

Rising en masse from the ground is particularly spectacular way of showing that you’re ready to reproduce, but the big majority of creatures has some signal. If you’ve visited a zoo, you may have seen those swollen pink rumps on female chimps, proclaiming that they’re in a period of fertility. Other creatures release tantalizing smells or put up other signs that say they’re open for reproductive business.

Though it’s pretty clear when humans reach sexual maturity—one might argue that the flood of hormones around puberty creates the societal equivalent of the cicadas’ roar—we don’t actually show when we are fertile. The days in a woman’s monthly cycle when she has an egg slotted into position, ready to be fertilized, are very well-hidden, even from the woman herself. A 2007 study found that lap-dancers got significantly more tips from male customers when they were fertile, suggesting that there may be signs that no one is consciously aware of; that study has spawned (so to speak) a line of research on other evidence that women’s ovulation is somehow perceptible. In any case, compared with most other animals, the clues are extremely subtle. Instead, women look like they could be fertile anytime. We don’t usually think of it this way, but having breasts that continuously protrude, rather than just when one is in heat or pregnant, is pretty weird in the animal kingdom.

It’s still mysterious why humans are so different in this respect—what our species might have gained from keeping our reproductive status under wraps. It could be that looking fertile all the time, even when one is not, means that males have to stick around all the time in order to ensure that they have offspring live to reproduce. This could mean that couples have to commit to one another long-term, with each contributing to the raising of some very time- and resource-hungry offspring—a good thing for infant survival. Or it could be that uncertainty over whether a given female is fertile means that there’s less conflict between males to mate with her and hence less violence within a population. Or maybe that not knowing for sure that a baby is one’s own cuts down on infanticide, a method used by male chimps to eliminate competitors’ offspring.

At this point, there’s no consensus as to what might have happened to make this our status quo—these are all stories spun by scientists to help get a handle on the problem. But they are something to consider while listening to cicadas drone and reflecting on how funny it is to witness a distantly related species’ grandiose fertility peak, while our own remains a secret.


Veronique Greenwood is a former staff writer at DISCOVER Magazine. Her work has appeared in Scientific American, Popular Science, and the sites of Time, The Atlantic, and The New Yorker. Follow her on Twitter here.


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