A shared preference in humans and chimpanzees
A new study from researchers at the University of Neuchâtel, published in The Royal Society Open Science, compared the preference for prosocial behaviour, e.g. cooperation, in humans and chimpanzees. Their results uncover surprising similarities that add to our knowledge on the origins of the extraordinary human collaborative and communicative abilities.
By the NCCR Evolving Language
Humans are extremely prosocial beings – they are eager to cooperate, help others, share resources… even when there are no obvious benefits for them. While these behaviours are more complex, frequent and on a larger scale in humans, they can also be found in other species, such as cleaner fish collaborating with their clients, or wolves hunting together. Among our closest relatives, the great apes, prosocial behaviours exist, but to a lesser degree.
In a new study published in The Royal Society Open Science, researchers from the University of Neuchâtel and the NCCR Evolving Language explored where this difference may come from, asking a fundamental question. Why did humans evolve into hypercooperative beings with complex communication systems, while chimpanzees did not? Could the difference lie in their ability to perceive prosocial actions?
Testing perception instead of reaction
Previous experiments have measured the prosocial abilities of chimpanzees through action-based responses, i.e. how individuals behave in cooperative tasks. “In our study, we chose to move away from action-based responses, which can be influenced by methodological approaches, and instead focus on the perceptual level,” Sarah Brocard, first author of the study, explains. “This approach places a greater emphasis on social knowledge, as behaviour may not reflect the ability to perceive what is prosocial.”
For this, using touchscreens, they tested the perception and preference of both humans and chimpanzees for prosocial agents. “Testing preference and not only recognition gives us a better understanding of cognitive processes at stake, reflecting motivation toward an element after its recognition,” she enunciates. The participants were shown videos where an agent acted on another, in a prosocial, neutral or antisocial way, as determined by external evaluators. After each video, participants could touch either actor, hinting at their preference.
The experiment was conducted on both species in a similar way: chimpanzees of the Basel Zoo interacted with the touchscreen inside a Plexiglas box in their enclosure, while humans used a similar screen in a university office. “The idea was to make the testing environments as comparable as possible across species,” the researcher says.
Like human, like chimp
After comparing the responses of humans and chimpanzees, the researchers saw no notable differences. “In both species, this choice was similarly influenced by the perceived prosociality of the agent,” Sarah Brocard says. “According to our results, humans and chimpanzees do not differ in how they perceive and choose between agents in third-party interactions.”
Though they were not particularly surprised to find a preference for prosocial agents in chimpanzees, they expected them to also prefer antisocial agents, given earlier evidence. “This absence of preference was somewhat unexpected, and it reinforced the idea that humans and chimpanzees express similar preferences,” the researcher shares.
In future research, she would like to test chimpanzees from different groups with varying levels of social tolerance, since it may influence prosocial behaviours. “Ideally, we would also expand our video set to include a wider range of behaviours, from more strongly antisocial to more strongly prosocial,” she adds.
Language and evolution
“Cooperation, and ultimately hypercooperation, can only evolve if individuals can perceive interactions as cooperative or prosocial,” says Sarah Brocard. This perceptual ability is a prerequisite for such behaviours to evolve.
The research group previously showed that humans and chimpanzees share a cognitive bias toward agents – the doer of an action. This shared bias may have shaped how our ancestors perceived social events, helping to organize perception in ways that supported the development of more complex communication, and eventually language. “In this study, we wanted to explore whether that cognitive bias could be influenced by the prosociality of the agent,” the researcher explains. “Our findings suggest that the differences between chimpanzees and humans we see today in cooperation and communication did not stem from how our last common ancestor perceived social behaviour, but rather from what evolved later on top of that shared perceptual foundation,” she concludes.
