Global experiment supports Darwin’s century-old hunch about auditory aesthetics

People tend to favor the exact same mating calls that female frogs, birds, and insects find most attractive in their own species. This overlap in auditory taste suggests that humans and other animals process sounds using similar sensory traits shaped by millions of years of evolution. The findings were recently published in the journal Science.

Across the natural world, male animals use a variety of signals to attract a mate. These signals range from the bright colors of butterfly wings to the elaborate songs of birds. Female animals receive these signals and show a distinct preference for certain traits over others. A female might choose a mate based on the depth of his call or the addition of extra acoustic flair.

These choices often stem from the way an animal’s nervous system is wired. Certain sounds provide greater stimulation to the auditory system, making them naturally more appealing to the listener. Because many species share similar nervous system structures, a sound that stimulates a frog might also stimulate a person. Charles Darwin originally suspected this shared appreciation, proposing that humans and animals possess similar aesthetic tastes.

A team of biologists and psychologists wanted to test Darwin’s century-old hypothesis using modern data. Logan S. James, a biologist at the University of Texas at Austin, led the investigation. James and his colleagues sought to determine if human listeners share the same subjective preferences as female animals listening to male courtship calls.

“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,” James said. “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 researchers designed an online game to test human preferences for a wide variety of animal calls. They recruited more than 4,000 volunteer participants from around the world to play this game on their computers and mobile devices. During the activity, participants listened to pairs of sounds produced by male animals from sixteen different species. These species included various frogs, birds, mammals, and insects.

Prior field studies had already established which sound in each pair the female animals preferred. The researchers only used audio recordings from these past studies to ensure the animal’s choice was well documented. As the participants listened to the pairs of natural recordings, they were prompted to select which sound they liked more. The participants did not know which sound the female animals actually preferred.

The research team used recordings that had been manipulated in past experiments to isolate specific audio traits. For example, some frog calls had been digitally altered to change their frequency or pitch. Other recordings captured natural variation in the wild, such as the difference between an ancestral cricket chirp and a newer cricket purr. This variety allowed the researchers to test a wide range of acoustic features.

Samuel A. Mehr, a psychology researcher at Yale University and senior author of the study, noted the benefits of this online approach. “In gamified citizen science, people volunteer for experiments simply because they’re fun and interesting,” Mehr said. “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 discovered a broad overlap between the sounds humans liked and the sounds animals liked. When an animal showed a very strong preference for a specific mating call, human listeners were highly likely to pick that exact same call. This agreement occurred across all the major animal groups tested, including birds, mammals, frogs, and insects.

When participants agreed with the animal’s choice, they also made their decisions about 50 milliseconds faster. This quicker reaction time suggests the appealing nature of the sound was processed rapidly by the human brain. The human participants also showed high internal consistency in their choices. When the game played the same pair of sounds a second time, the participants generally picked the same sound they had chosen before.

The team looked closely at the specific acoustic traits that humans and animals found appealing. Humans and animals both favored calls that included acoustic adornments. An acoustic adornment is an extra sound added to the end of a basic call, like a trill, click, or a low-pitched chuckling noise. Humans and animals also both favored ancestral sounds, which are basic calls that have existed for a very long time in a species’ evolutionary history.

There were a few instances where human and animal preferences did not align. Humans showed a distinct preference for lower-pitched sounds across the board, while the non-human animals did not share this specific preference for lower pitches. Humans also preferred the songs of birds that had grown up in isolation. In contrast, the female birds preferred the songs of males that had learned their tunes from older tutors.

The team also checked if a participant’s background influenced their choices. They assumed that birdwatchers or expert musicians might align more closely with animal tastes due to their trained ears. The data showed no such connection for musicians or animal experts. The results for these groups were not statistically significant when compared to the general public.

The only trait that predicted a higher agreement with animal choices was the amount of time a person spent listening to music each day. The researchers suspect that frequent music listening might lead to better auditory discrimination skills. These enhanced listening skills could translate into a higher agreement with the aesthetic choices of animals.

Michael J. Ryan, a biology professor at the University of Texas at Austin and co-author of the study, explained the broader meaning of these shared tastes. “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.”

The researchers noted a few limitations regarding the study’s scope and the nature of animal preferences. Animal preferences in the wild are highly dependent on context and can vary widely among individuals in a single population. This natural variation makes it difficult to pinpoint exactly which call is universally preferred by a species. The researchers had to rely on average preference rates from past studies, which inherently includes some uncertainty.

Additionally, the researchers struggled to find a single acoustic feature that perfectly predicted attractiveness across all species. Biological preferences likely arise from multiple audio cues blending together rather than one specific trait. A sound might need a specific combination of pitch, length, and volume to appeal to a particular species. This makes it challenging to draw sweeping conclusions about the exact nature of an attractive sound.

Future research will need to explore how these different sound features interact within the auditory systems of various species. Scientists hope to investigate whether this shared appreciation for sound extends to other sensory experiences. They want to know if humans also share animal preferences for visual patterns or physical courtship dances. Until then, these findings provide strong support for the idea that a basic sense of aesthetics is deeply rooted in our shared evolutionary past.

The study, “Humans share acoustic preferences with other animals,” was authored by Logan S. James, Sarah C. Woolley, Jon T. Sakata, Courtney B. Hilton, Michael J. Ryan, and Samuel A. Mehr.