Frogs, birds, monkeys, and humans make a variety of sounds expressing emotions. And because that ability is shared by every land-dwelling animal with a backbone, Charles Darwin argued that these cries have a common origin.
Humans can recognize the emotions in the voices of other mammals, including cats and dogs. To find out whether we can also do this for nonmammals, scientists gathered recordings from nine species, including the hourglass tree frog (above), American alligator, common raven, Barbary macaque, and Tamil-speaking humans in two emotional states: highly and mildly aroused. They played the calls to 75 people—men and women who spoke English, German, or Mandarin—and asked them to judge whether the animal was very excited or subdued. You can try it yourself below:
Participants easily passed the tests. Some 90% of listeners distinguished between the excited and calmer sounds of the tree frogs (which were calling for mates), and 87% scored the alligator calls correctly. Sixty-two percent were right about the ravens’ calls of alarm.
The results suggest there are some “universal” vocal elements, like calling at a higher frequency, that convey emotions across taxa, the scientists report today in the Proceedings of the Royal Society B. That may also mean, say the scientists, that our ability to infer how an animal is feeling is indeed rooted in biology.