Prejudice in humans has ancient evolutionary roots

The tendency to perceive others as "us versus them" is not exclusive to humans, but also exists in some of our cousins ​​- the primates. This is according to a new study led by researchers at Yale University and with the participation of Prof. Gil Dizandrok from the Department of Psychology and the Gonda Center for Brain Research at Bar-Ilan University and researchers from Harvard University

The tendency to perceive others as "us versus them" is not exclusive to humans, but also exists in some of our cousins ​​- the primates. This is according to a new study led by researchers at Yale University and with the participation of Prof. Gil Dizandrok from the Department of Psychology and the Gunda Center for Brain Research at Bar-Ilan University and researchers from Harvard University.

In a series of experiments, researchers led by psychologist Lori Santos showed that monkeys treat individuals outside their group with the same suspicion and resentment that humans tend to attribute to strangers, suggesting that the conflict between the different human groups has strong evolutionary roots. The findings were reported in the March issue of the Journal of Personality and Social Psychology.

"One of the more troubling aspects of human nature is that we evaluate people differently depending on whether they are our 'ingroup' friends or 'outgroup' strangers," Santos said. "To a large extent, all the conflicts in human history have involved people who discriminated based on who shares with them race, religion, social status, etc. The question we were interested in, where do these diagnoses come from?"

The answer, she adds, is that such biases have probably been shaped by 25 million years of evolution and not just by human culture.

Santos and the people in her lab studied the rhesus monkeys living on an island off the coast of Puerto Rico. Like humans, monkeys in this population naturally live in different social groups based on family history. To assess whether monkeys made the distinction between individuals in the same ingroup and between outgroup strangers, the researchers used the well-known tendency of animals to look longer at new or fearful things than at familiar or friendly things. They presented the monkeys, side by side, pictures of monkeys that were from their own social group or members of another group. They found that the monkeys stared longer at pictures of other monkeys that were outside their group, suggesting that the monkeys spontaneously recognize who is a stranger and who is a member of their group.

"What made this result even more impressive," noted Neha Mahajan, a PhD student at Yale University who led this project, "is that monkeys in a population move from group to group, so some of the monkeys that were strangers were previously members of the same monkey's group, but However, the results are also significant for monkeys who moved from group to group only a few weeks earlier. This indicates that these monkeys are sensitive to their current group members. In other words, even if the monkeys divide the world into 'us' and 'them', they do This is in a flexible manner and they update their decisions in real time."

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Santos and her colleagues then asked whether monkeys evaluate ingroup members and outgroup members differently ie do they associate them with "good" and "bad" respectively? They developed a monkey version of the hidden attitudes test (IAT) that is usually done on humans. In humans the test measures the degree of bias of humans towards members of other groups. To test the same feature in monkeys, the researchers showed the monkeys a sequence of pictures in which the pictures of members of their group and of monkeys from other groups appeared in pairs together with good things such as fruit or bad things such as spiders.

The researchers measured the amount of time the monkeys stared at the two types of image sequences. It turned out that they stared longer at their non-constant value image sequences than constant value sequences. For example, he stared more at a sequence consisting of pictures of other-group monkeys (negative) and fruits (positive) than at a sequence of other-group monkeys and spiders (both negative). Like humans, monkeys spontaneously tend to see members of their group as good and members outside their group negatively.

"Because both humans and rhesus monkeys make distinctions between 'us' and them, the roots of prejudice in humans date back 25 million years when humans and rhesus monkeys share a common ancestor."

Social psychologists introduced to the world the idea that the immediate situation has a huge influence in determining behavior, including intergroup feelings, says Mehazarin Banjai from the Department of Psychology at Harvard University and a co-author of the article. "The evolutionary theories make us aware of our past. In this work we connect the years and show the importance of both influences in this work."

"The bad news is that the tendency to hate members of other groups has an evolutionary history, and will therefore be less straightforward to reverse than we would like to think." Santos said. "The good news is that even apes are flexible about their group members. If humans find ways to exploit this flexibility, it might make us a more tolerant species."

Dizendrock does build on this potential flexibility, and for years has been conducting research on the development of Israeli children's views on in-groups and out-groups. His research shows that from an early age secular and religious Jewish children, and Arab children demonstrate a belief that the two nationalities are fundamentally different from each other, and that this cannot be changed.

Recently, Dizandrok started an innovative study in his laboratory at the Gonda Center for Brain Research at Bar-Ilan University, where he and a team of students are trying to test the process of creating social groups in 9-11 month old babies. Those interested in hearing more about it, or participating in research, Welcome to visit the site.