As humans, we share many characteristics with other primates, such as bonobos, who – together with chimpanzees – are the ape species most closely related to us. While there are many similarities in the social behavior of bonobos and humans, a team of researchers led by Leiden University and the University of Amsterdam has recently found that there are also remarkable differences.
The experts discovered that, although both species are more interested in photos of conspecifics that show emotion than in neutral photos, human attention is more easily drawn to photos of family members or friends, whereas the attention of bonobos is drawn to the emotion of individuals they don’t know.
In a first experiment, the scientists trained bonobos from the Apenheul zoo to press a dot on a screen. After pressing it, two images appeared briefly that showed bonobos from the same group as well as unfamiliar conspecifics. While some images were neutral, others expressed emotions related to fear, play, or sex. Then, a dot appeared again behind one of the two images, and the bonobos had to touch it as quickly as possible in order to receive a food reward.
The researchers kept track of how fast the bonobos pressed the dot that appeared after seeing the different pictures, with the presupposition that the apes would be faster at touching the dot behind the photo that immediately grabs their attention.
A second experiment presented people visiting the zoo with the same task, with photos of strangers or a person with whom they visited the zoo that day, and with varying facial expressions, such as neutral, happy, angry, or scared.
“In these studies, we saw that both humans and bonobos react more quickly to photos of conspecifics with an emotional charge than neutral photos,” said study lead author Evy Van Berlo, a postdoctoral researcher in Cognitive Behavioral Ecology at the University of Amsterdam. “That is what we expected: it makes sense given that we are both social animals. Yet there was also a remarkable difference. We humans are mainly focused on emotionally charged photos of people we know, while the attention of bonobos is focused on studying emotionally charged photos of unfamiliar others.”
According to the researchers, this evolutionary difference has probably emerged due to differences in the living environment of the two species. “Bonobos live in a relatively stable ecological environment in Congo, where there is enough food available. Under those circumstances, there is less need for competition with other groups and peaceful interaction with strangers might even be beneficial for the conservation of the species. Early humans, on the other hand, lived in nomadic groups that had to compete with other groups of humans for food. Under such circumstances, it is probably evolutionarily more beneficial to favor individuals from your own group over strangers,” Van Berlo explained.
In future research, the scientists plan to repeat this study with other species of great apes with different social organizations, such as chimpanzees, which are more competitive, male-dominated, and socially stratified. “With chimpanzees, for example, I would expect them to be more interested in the emotions of individuals they know than the emotions of strangers,” Van Berlo concluded.
The study is published in the journal Emotion.
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