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This frog sexbot can teach you about evolution

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Sometimes you just have to build a sexbot for science. And when you're studying the mating habits of frogs, well, that means you're going to need some pretty specific moving parts. The best part? Something fascinating is revealed about evolution when you watch video of this frog sexbot in action.

But first, some backstory on why there was a frog sexbot in the first place. Biologists Michael Ryan and Ryan Taylor wanted to find out how frogs would react to mating calls that didn't perfectly mirror what they would typically hear and see in nature. Would the frogs only be lured by perfectly reproduced mating behavior, or would a rough approximation be enough to arouse their interest? So they had to devise a frog sexbot that would act like a male frog trying to attract a mate — but with a few slight deviations from the typical frog mating ritual.

In a release about the study, we learn more about how Ryan and Taylor devised their experiment:

When choosing a potential mate, female túngara frogs listen to the sounds of the male calls, which are based on a pattern of "whines" and "chucks." If visible, the sight of the male frogs inflating their vocal sacs adds to the appeal of the calls. It makes a whine more attractive, though still less attractive than a whine-chuck, and it makes a whine-chuck more attractive still.

In an innovative experiment, [Ryan and Taylor] played around with those visual and auditory signals. They took a recording of a basic whine, then added a robotic frog that inflated its vocal sac late. They ran a parallel experiment with a chuck that arrived late relative to the whine.

On their own neither the late vocal sac expansion or the sluggish chuck added to the sex appeal of the whine. In both cases it was as if the frog had just whined.

When the late cues were strung together, however, something extraordinary happened. The vocal sac "perceptually rescued" the chuck and bound it together with the first part of the whine-chuck call. The resulting signal was as attractive to the female túngara frogs as a well-timed "whine-chuck."

"It never would happen in nature, but it's evidence of how much jury-rigging there is in evolution, that the female can be tricked in this way," said Ryan.


Here's the frog sexbot attracting a mate in their video:

What Ryan means when he says there's "jury-rigging in nature" is that our brains don't always rely on exact inputs from the outside world to discover meanings. The two biologists say that what the female frog did with her sexbot is similar to what your brain does in "continuity illusion" tests. In these tests, a lot of white noise is played in between blip sounds. With enough noise in between, your brain hears those blips as a single, continuous sound instead of blips interrupted by noise. (This is similar to what our brains do in "persistence of vision" illusions for the eyes.)


The female frogs were basically knitting together the whine and chuck noises in their minds, pulling meaning out of a noisy, confusing situation — kind of like the way you can reconstruct what somebody has yelled in a noisy bar based on a few snatches of words and hand movements. According to Ryan, this means the frogs have adapted to have flexible reactions to communication in noisy environments. In a release, he said:

We need to be able to hook things together perceptually in unexpected ways to extract meaningful stimuli from a lot of noise. So what we think is happening here is that the vocal sac, the visual cue, is working kind of like the white noise, giving perceptual continuity between these two sounds, binding the temporally displaced whine and chuck together.


Ryan believes the study helps illuminate how animals evolve complicated behaviors, like the multiple signals these frogs use to mate. If you couple an ability to extract meaning with chaotic situations, one possible result would be that frogs would evolve new ways of communicating and perceiving information over time. This neurological ability could certainly help frogs behave more flexibly in new situations.

This study could also shed light on human intelligence, which is based in part on our ability to put many sounds together and create complex meaning out of them. Perhaps language evolved from much simpler kinds of communication, like these frogs', that became more elaborate over time.


This study might also might explain why humans love sexbots so much. No, really. Think about it.

You can read the full scientific study in Science.