The bright colors of butterfly wings, the sweet aromas of flowers and the euphonious melodies of songbirds all evolved as signals that help individuals propagate, yet humans also find these very same signals pleasing to their own senses. In a study published today, Mar. 19, in Science, scientists from the Smithsonian Tropical Research Institute (STRI) collaborated with researchers in U.S., Canada, and New Zealand to show that humans and animals not only express the same subjective preferences for one type of signal—particular animal mating calls. In addition, across the range and complexity of the animal sounds found in nature, humans and animals show overlapping preferences for certain qualities of an animal's call. These findings indicate that preferences for some animal sounds are more universal than previously known.
In the early 1980s, STRI staff scientist A. Stanley Rand and STRI research associate Michael J. Ryan demonstrated for the first time that in the tropical rainforests of Central America, a female túngara frog's preference for a mate depends on the complexity of the male's call. In this new paper, Ryan, now also a professor at the University of Texas at Austin, and his colleagues wanted to know whether human preferences for certain animal calls, including those from male túngara frogs, correlate with the preferences of female animals.
"After witnessing those female preferences Stan and Mike discovered when I got to measure them myself, I became fascinated with the question of where these preferences come from," said Logan James, a STRI research associate and the study's lead author. "Plus, since that team released their initial findings, we've found that other animals, including eavesdroppers such as blood-sucking flies and frog-eating bats, also prefer complex calls. This got us wondering how common acoustic preferences may be."
The team tested humans' preferences for different animal sounds using an online computer game . More than 4,000 human participants from around the world were presented with pairs of animal sounds from 16 different species across the animal kingdom and were asked to express their preference for one or the other. The animal sounds were all recorded in previous research studies, and within each pair, the animal from which the sounds came is known to display a preference for one of the two. The researchers tested whether humans showed a preference for the same sounds the animals preferred.
"In gamified citizen science, people volunteer for experiments simply because they're fun and interesting," said Samuel Mehr, an associate professor at Yale University's Child Study Center and the senior author of the study. "The method is perfect for answering questions from evolutionary biology where we aim to study phenomena across many species as opposed to just a few. Our game enabled us to test lots of humans' preferences for lots of different sounds."
The research team found broad overlap between human and animal sound preferences. They discovered that the stronger an animals' preference for a particular sound, the more likely it was that a human was to select that sound as their favorite. And the human participants were quicker to select the more attractive sound. Agreement between animals and humans was strongest for lower-frequency (lower pitch) sounds and those with acoustic adornments, such as "trills," "clicks" and "chucks."
"Darwin noted that animals seem to have a 'taste for the beautiful' that sometimes parallels our own preferences," Ryan said. "We show that Darwin's observation seems to be true in a general sense, probably due to the many sensory system properties we share with other animals."
About the Smithsonian Tropical Research Institute
Headquartered in Panama City, Panama, STRI is a unit of the Smithsonian Institution. Our
mission is to understand tropical biodiversity and its importance to human welfare, to train
students to conduct research in the tropics, and to promote conservation by increasing
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