Could the menstrual cycle have shaped the evolution of music?

A piece of advice I once received: Don’t ever talk about your period at work. No one wants to know.

I have broken that rule. Menstrual cycles are fascinating, and at the risk of a major breach of workplace etiquette, here’s why we should all be talking about them more: If you’re a woman, your cycle shapes your physiology more than you probably realize, with hormones orchestrating a monthly chemical waltz through your brain and metabolism. And men, it wouldn’t kill you to understand more about the menstrual cycle than what PMS is.

A lot of recent research has moved beyond PMS to try to understand women’s cycles, and some of it, controversially, focuses on women’s sexual behavior around the time of ovulation. One new study, published April 22 in the Proceedings of the Royal Society B, even proposes that the menstrual cycle may play a role in humans’ musical abilities. It sounds bizarre, but the idea is that women’s preferences for men’s physical and intellectual abilities are more pronounced during the fertile part of the cycle. So a preference for more sophisticated musicianship during the fertile time of month, around ovulation, might have given men with more musical talent an advantage in mating. Over time the species would have become more musical, so the thinking goes.

Darwin once argued that human music might, like birdsong, serve mainly a courtship role. The idea has languished as another untestable tale of the evolutionary past. But now biologist Benjamin Charlton, who has also studied how koalas’ creepily deep voices might attract mates, revives the idea with this new study of how women’s preferences for men’s musical abilities change according to the menstrual cycle.

First, Charlton conducted experiments to see whether women had a stronger preference for either more complex or simpler music at different times of the month. They did not; women who listened to musical snippets generally tended to like more complex music a little better than simpler music, but there was no difference depending on whether they were more fertile (near ovulation) or not.

Next, Charlton had women (more than 600 in each group) listen to snippets of music and gauge their sexual interest in the man who (supposedly) composed each piece. This time, there was a menstrual cycle effect. Women who were not near ovulation had no noticeable preference for creators of more or less complex music; their choices were about 50/50. But women who were in the ovulatory week preferred the more complex music-makers as potential short-term sexual partners, with about three-quarters of women preferring the complex composers and a quarter preferring simple composers.

There was no effect on the women’s stated preference for long-term partners, which is consistent with other research (and common sense) that shows long-term partners are chosen for complex reasons that often have nothing to do with genes or producing children.

As for the menstrual cycle’s link to music’s past, “obviously we can’t go back in time and witness evolution as it’s occurring,” says evolutionary psychologist Martie Haselton of the University of California, Los Angeles. “But even if we can’t know for sure that musical complexity evolved to attract sex partners, these results do leave us to ponder that question more.”

Other studies, including Haselton’s, have suggested that women are more attracted to certain traits during the fertile part of the cycle, including testosterone-driven features like deeper voices, a muscular physique and masculine faces, but also creative intelligence. “Any clue that indicates a male’s ability in an area that could garner resources and provide for a female partner could also provoke more interest in women when they are fertile,” argues attractiveness researcher David Perrett of the University of St. Andrews in Scotland.

The truth is, we still don’t know a lot about the menstrual cycle. In recent years, neuroscientists have started to learn more about how hormonal fluctuations during the cycle affect the brain, famously for mood but also in parts of the brain dealing with rewards. That could play a role in addiction, and other cascading effects may even shape aspects of learning and memory.

And here’s where we all start getting nervous. All this talk about hormones and cycles feels, frankly, sexist. I don’t want my colleagues to think I’m “ruled by hormones.” Women have worked very hard to fight the stereotype that says a woman can’t be a soldier or a president because she’ll get all weepy and emotional every month. It’s insulting.

But that fear of appearing weak, or of simply being different from men, holds us back too. It keeps us from understanding our own bodies. And it prevents us from recognizing how women’s preferences for sexual partners has shaped our species.

“There’s still an old school of feminism that denies that there are sexual differences,” Haselton says. “Ironically enough, I think that the people who bristle at the notion that women’s hormones affect their behavior are motivated by feminist ideology, but I actually think there’s more sexism in denying that hormones might affect women’s behavior, when that denial is based on the idea that women’s hormones somehow make them irrational.”

It’s common for nonhuman females to change their behavior around the ovulation cycle, but people seem to have a hard time believing that such differences apply to humans. “Nonhuman primate females show changes across the cycle in how they respond to potential mates, and indeed how potential mates respond to those females depending where they are in their cycle,” Haselton says. “Because there weren’t such obvious changes across the cycle in humans, people believed that hormones just really didn’t matter in human sexuality.” 

Just to be clear, even if hormone levels do affect women’s sexual preferences, that doesn’t mean women go on autopilot when they’re ovulating. Human behavior is complex, and the studies that have seen effects of ovulation are looking at shifts in what’s rated as sexually attractive on average by women, not what any particular woman actually does in a given situation. 

We may never know if sexual behavior was responsible for the evolution of human musicality. This is just one study, and even if women’s preferences for complex musicianship holds up in further studies, that’s a long way from proving anything about the evolution of music in our ancestors.

But what if it’s correct? Not only would that make it pretty clear that what women want matters, but imagine this: What women want has made us who we are, musical geniuses and all.

I’ll try not to let the power go to my head.

So yes, our hormones set off a monthly chain reaction that we are only just beginning to understand. That’s nothing to be ashamed of. And just maybe we, like every other animal on the planet, behave a bit differently when our sexual context changes. Get over it.

Oh, and lest men think they’re off the hook for hormones, I would just like to point out that testosterone affects the brain and behavior, too. “And the thing about men’s hormone cycles,” Haselton says, “is that they are every day.”

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