Orangutans base their food choices on whether others appear to be having a good time, research suggests. Scientists studying captive orangutans have found that when the great apes heard the sound of their peers laughing before they searched a bowl for a tasty treat, they valued the reward more highly. Erica Cartmill, a professor of anthropology and cognitive science at Indiana University and senior author of the work, said the study is part of a larger project exploring whether animals feel joy and what the implications of those emotions are in areas such as cognition and learning.
The researchers first trained the orangutans to search through bowls to find food treats. They then presented each orangutan with two bowls. One contained a tasty morsel buried under a harmless substance such as moss or sawdust, while the other contained a different type of material but no treat.
Crucially, just before the researchers presented the bowls to the orangutans, they played a recording. This was either the sound of orangutans playing and laughing or environmental sounds such as wind, with the choice of soundtrack depending on which of two substances was used to cover the food that day. On the fifth day the team presented the orangutans with two bowls, but this time each contained a treat buried beneath one of the two food-covering substances.
They then asked the orangutans to pick a bowl. The results from multiple trials revealed that, overall, the apes preferred to pick the bowl containing the substance associated with the sound of laughter, with four of the six orangutans showing a clear preference. Cartmill said the preference could be rooted in the sound of laughter putting the orangutans in a more positive emotional state when they learned to associate the substance with food.
Dr Adriano Lameira, a primatologist and evolutionary psychologist at the University of Warwick, who was not involved in the work, described the results as fascinating. Cartmill added the results suggest it is not only the quantity or frequency of a reward that can be important when learning associations. She added that could be useful in helping to understand why some information is more trusted or why students choose to continue studying certain subjects.
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