A new study from Indiana University shows that being in a positive mood leads orangutans to value what they learned more strongly. The study comes from the lab of Erica Cartmill, professor of animal behavior, anthropology and cognitive science in the College of Arts and Sciences at IU Bloomington, and was led by Daan Laméris, a postdoctoral researcher at IU.
Scientists have long acknowledged that in humans, positive moods enhance learning and make experiences more memorable. However, the evolutionary origins of this trait haven't been studied in other great ape species.
Laméris and Cartmill hypothesized that if orangutans heard laughter while learning how to find a reward, they might value that reward more. Laméris designed a study that took place over five consecutive days to test this hypothesis.
The power of laughter
In the study, the orangutans were presented with two bowls containing different materials they had to dig through to find a food reward. On days one and three, food was always hidden under one material (e.g., wood chips) and never under the other (e.g., paper towels).
On days two and four, the same unrewarded material was presented, alongside a new material (e.g., yarn) that now covered the reward. On the fifth day, the researchers brought back the two materials that had previously hidden rewards to see which one the orangutans preferred.
The orangutans had learned that food rewards were hidden under both wood chips and yarn, so they shouldn't prefer one over the other when looking for the reward.
However, the important difference was that the researchers had played the sound of orangutan laughter when the orangutans were searching in one material, and a control sound when the orangutans were searching in the other.
When given a choice between both hiding places, orangutans preferred the material that they dug through when listening to laughter.
Because laughter is contagious for all great ape species, it can impact mood positively. Cartmill and Laméris concluded that hearing laughter puts orangutans in a more positive mood and causes them to value a reward more.
"It is surprising to find these effects with orangutans, because they are the least social of all the great apes," said Laméris, who conducted the majority of the orangutan study at ZOO Planckendael in Mechelen, Belgium. "So even among relatively non-social animals, laughter is important."
Cartmill likens this to something that happens with humans: You might like your grandma's pancakes the best not because they are objectively the greatest pancakes ever made, but because you have positive associations with eating that food at a loved one's house.
"What we've shown in this study is that we can measure the value of laughter, and we can measure how much mood is valued," Cartmill said. "When you're in a better mood, the memories you form are remembered more positively and have more value to you."
Thriving, not just surviving
Cartmill wanted to study positive emotions like joy in animals because she said the scientific scales tend to be tipped toward studying fear, grief and loss in animals, contributing to a narrative that nonhuman animal life is only about competition and survival.
"Part of this project was to ask, 'What are the moments that help shape the lives of the animals we share a planet with?,'" Cartmill said. "It isn't just about surviving to reproduce, but it's actually about creating a narrative that also involves friendships and memories and building toward the things that give life meaning."
