When a cat purrs or a dog yelps, people can often contextualize the animals’ sounds to be in response to pleasure or pain. Now, new research finds that humans also have the ability to infer certain behavioral information from the sounds that chimpanzees make, suggesting a “phylogenetic preservation” of acoustic features throughout the course of human evolution.
“When we hear a hissing cat or a person laughing, we may be able to infer information from these vocalizations, including both the individual's affective state and the kind of situation they are in,” write the researchers in Proceedings of the Royal Society B.
Charles Darwin hypothesized in 1872 that emotional vocal expressions have “ancient evolutionary roots” based on shared mechanisms across mammalian species. Most research has focused on the production of noises by animals, but not other species’ ability to understand and contextualize what they mean. Many vocalizations can be linked to the emotional state of the individual making the sound, and these vocalizations tend to be species-specific.
In order to determine human listeners’ ability to perceive the behavior of chimps based solely on their vocal sounds, researchers from the University of Amsterdam, the University of York, and the Max Planck Institute for Evolutionary Anthropology conducted two experiments employing 155 vocalizations from 66 chimpanzees in 10 different situations, some of which were positive and others that were negative. Thousands of human volunteers were asked to listen to the chimps’ sounds and then categorize them based on 10 types of behavior, such as copulating or aggression. It turns out, people weren’t great at this task, so researchers instead played a sound and asked the volunteers to say whether or not it corresponded with a behavior listed on a computer screen.
People picked up on cues of “brightness” and “duration” as well as “noisiness and pitch.” By and large, they were good at determining when a chimp found a good meal or was denied food, but not so great at picking up cues of copulation or a juvenile being separated from their mother.
“Overall, the results suggest that human listeners can infer effective information from chimpanzee vocalizations beyond core effect, indicating phylogenetic continuity in the mapping of vocalizations to behavioral contexts,” write the study authors.
Understanding cross-species communication could help researchers clue into parental behavior and sexual partner selection, as well as gather information about an individual’s “inner state” to help facilitate “adaptive behavior” in a number of contests, such as being attacked by a predator. Human inference of chimp behavior suggests a potential learning pattern and communication that has followed through the course of evolution, further helping to bolster survival skills in the wild.
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