Eccentric's Corner: The Croaks of Seduction

Michael Ryan has spent decades studying a tiny, bumpy frog that offers clues to universal laws of romance.

By Gary Drevitch, published March 1, 2018 - last reviewed on May 1, 2018

To understand what beauty is, we need to understand the brain that perceives it," University of Texas biologist Michael Ryan writes in A Taste for the Beautiful. "The details of an animal's brain give rise to its sexual aesthetics, which in turn drive the evolution of beauty in that species." This is the core of the theory of sensory exploitation, which Ryan has explored over 40 years of field work with the tungara frogs of Central America. He believes that they have a lot to teach us about why our own romantic strategies succeed or fail.

LOVE DENS: Michael Ryan has studied tungara frogs in the montane forest habitat of Panama's Chiriqui province for four decades. (Photo courtesy of Ximena Bernal)

For you, the idea that beauty is in the eye of the beholder is no cliché but a law of nature.

I say that beauty is in the brain of the beholder. All of these animals have evolved very different sexual displays. Where do these differences come from? They come from the fact that you have different brains judging what's attractive.

How did you decide that tungara frogs were the creatures that would become your life's work?

I started studying frogs as a graduate student in the mid-1970s, and I thought that after my thesis I'd move on. All frogs make calls that identify them by species. We knew that the frog's auditory brain found calls of the same species more attractive, but when I started listening to these guys, I could tell a lot of the individual males apart just by hearing them. I wondered if the females could, too. 

So you stuck with the frogs.

I went to Panama to study red-eyed tree frogs to see whether differences in calls translated into differences in perceived attractiveness. Those frogs mostly breed up in the canopy, though, and it was hard to record them. But I had all of these noisy little tungara frogs at my feet that I kept kicking to shut them up. It became obvious that they were not only more accessible but also more interesting. 

What have they taught you about attraction?

That the females are in the driver's seat. They decide what's attractive. Darwin suggested that, like humans, female animals have aesthetic senses—a taste for the beautiful—and that's why males evolve all of these traits that don't enhance their survivorship at all. They do the opposite: These are traits that kill.

That's a real problem for the frogs: The calls that best attract females also attract predatory bats.

When we play calls in the forest, the bats come out of the canopy, land on the speaker, and try to rip it up to get inside. Just like the female frogs, they're most attracted to a call that's a whine with multiple staccato sounds known as "chucks." The difference is that the females are looking for mates and the bats are looking for meals. 

How much are we like the frogs? Do men recalibrate their pitch to attract a female who may not be responsive, or do they move on to others who may respond more positively?

Frogs and humans both experience the "closing time" phenomenon: As closing time approaches, a guy in a bar convinces himself that the women who are left are more attractive than he thought they were earlier in the evening. With frogs, when we replayed calls late at night that females wouldn't respond to earlier, all of a sudden those calls were attractive. For the frogs, it's better to mate with an inferior male than not to mate at all. With humans, it probably has more to do with reducing cognitive dissonance.

Humans rely on multiple modalities of attraction—sight, sound, and smell. Is that rare?

It's not unique. The frogs that we work with are primarily auditory, but frogs call in the water, and their vocal sac inflates and deflates, creating ripples. Much like lip reading, females can extract information from the visual cues of the vocal sac and the seismic cues of the ripples. Birds are both visual and auditory: Males will sing or display. As for us mammals, we also pay a lot of attention to the olfactory, too. 

But we don't realize it.

In a famous experiment, women sniffed men's T-shirts and then rated the owners' attractiveness. They found the guys with different histocompatibility genes from their own—these are genes that influence our sexual attraction—to be more attractive, but there's a caveat: That's only if you're not taking oral contraceptives. If you're on the pill, you don't have that preference. I've seen speculation about what might happen if a couple starts to date while the woman is on contraceptives, and then she stops taking the pill. Does this lead to problems?

That's an interesting question.

I once met with a screenwriter who had a lot of questions about odor and humans. He was writing a comedy about a woman who hooks up with a sexy, rich young man, but then she goes horseback riding, falls, and breaks her nose. Now, all of a sudden, she doesn't like her boyfriend at all, and this lazy janitor who's been hitting on her is really attractive to her. Unfortunately, it was never made, but I was going to play the evolutionary psychologist.