Laughter — closely tied to language and a sense of humor — has long been thought to be uniquely human.
But in a new study out of Indiana University, researchers have discovered that bonobos, the closest living relative to human beings, along with chimpanzees, tend to be more optimistic after hearing similar vocalizations during play with their fellow apes.
“We know that other apes, like chimpanzees, have contagious laughter during play,” said Dr. Sasha Winkler, a visiting research scholar in the Cognitive Science program at IU said in a statement
“We were wondering if that behavior could be explained by positive emotions produced from the sound itself.”
The findings, which were recently published in the journal “Nature,” have implications for understanding the evolution of positive emotions in humans and primates alike.
In the study, the researchers conducted a “cognitive bias test,” an animal psychology methodology that assesses the mood of animals based on how they interpret uncertain situations: More positively or more negatively.
First, they trained the bonobos to approach black boxes that always contained food rewards and to avoid white boxes that were always empty. Then, they would be exposed to either a control sound or bonobo laughter, and they would be presented with a grey box they had never seen before.
Their goal was to see if hearing laughter would make the bonobos more likely to approach an ambiguous stimuli, which is coded as a behavioral indicator of optimism.
Similar to humans, the laughter indeed made the bonobos feel more optimistic. Hearing the laughter of their fellow apes, the bonobos anticipated greater rewards when faced with ambiguous cues, namely, the grey boxes.
“Think of it like the rose-colored glasses effect,” explained Winkler. “The bonobos were much more likely to approach the grey boxes after hearing laughter, treating them like the rewarded boxes, and indicating a more optimistic expectation of finding a treat.”
“The tendency to behave more optimistically after hearing laughter suggests that the sound alone induced a positive emotional state in bonobos,” added Erica Cartmill, another lead researcher on the project and professor of anthropology.
“This is the first study of which we’re aware to measure a positive affect shift in non-human primates from a brief experimental intervention.”
The study also indicates that the bonobos experience emotional contagion, or the tendency to “catch” emotions from others, a concept researchers believe to be an important aspect of empathy.
“Studies like ours can help to untangle the evolutionary building blocks of empathy, communication, and cooperation in humans,” Winkler said.
Observing the positive emotional response in the apes encouraged the researchers to draw the conclusion that not only do great apes share laughter as an evolutionary trait with humans, in fact, human laughter likely stems from these sounds made by our primate ancestors.
The researchers also believe that, outside of the acoustic and behavioral similarities, laughter offers shared cognitive and emotional effects between humans and primates.
“Our results suggest that laughter in other apes shares not only phylogenetic and behavioral similarities with human laughter but also perhaps some of the same cognitive-emotional underpinnings,” said Winkler.
“This emotional contagion appears to have been present in the primate lineage long before the evolution of language.”
Beyond the stunning research further expanding on the relationship between humans and great apes, this research also paves the way in a growing body of research into the positive emotional states of animals.
“Our emotions influence many aspects of cognition, including memory, attention, and decision making,” Cartmill said.
“But research has historically focused on negative emotions with clear behavioral correlates, like fear and aggression. We wanted to better understand the relationship between positive affect and cognition in our closest living relatives.”
Hopefully, the researchers added, their work will encourage more studies on positive emotions in animals, especially those closely related to humans.
“We hope this brings greater public awareness to the remarkable similarities between us and bonobos, who are an endangered species,” Winkler said. “We have so much to learn from these incredible animals.”
Header image courtesy of The Ape Initiative
