Conflict and Cliques Primate Study Sheds Light On Group Bias

Although studies have looked at intergroup conflicts in animals, there has been no detailed analysis on the origin of these conflicts. The series of experiments in this study examined the conflict between social groups, using monkeys as experimental animals. The results showed that individuals in a group could identify those who did not belong there. Overall,  macaque monkeys viewed their group members more positively than non-group members. The authors concluded that the feelings of belonging to a group and lack of goodwill towards other groups is deep-seated and is similar in primates and humans.

Historically, wars and conflicts have arisen out of group feelings like racialism and other factors like ethnicity, class, religion and nationality. Although the triggers are different, human behavior of “prejudice, hatred and even large scale genocide” is similar in all these conflicts. These conflicts have been studied by social psychologists to understand humans’ antagonism towards those who do not belong to their group. No studies, however, have explained how these feelings come into being in humans and also whether it exists in all primates. This series of experiments was conducted to understand the feelings of conflict and bias without and within the groups, respectively.


  • In experiment 1, 37 adult macaques were shown pictures of other adults who may have or may not have belonged to their group. Similarly, in experiment 2 and 3, 39 and 40 monkeys, respectively, were shown pictures of members from the other group, who were later shifted to the participating monkey’s group.
  • For experiment 4 and 5, the pictures of outgroup and ingroup monkeys were covered with a novel object like a foam cut out as a donut etc. The time taken for the 79 tested monkeys to look at the pictures after removing the object was noted.
  • For experiment 6 and 7, pictures of ingroup and outgroup monkeys were teamed up with a pleasant (fruits) or unpleasant (spider) picture. Time taken to gaze at each of the combinations was measured.


  • Experiments 1 and 2 showed that the monkeys looked longer at faces (average 10.83 seconds) that belonged to outgroup monkeys than ingroups (average 6.58 seconds). Experiment 3 showed that the monkeys looked longer at faces of outgroup monkeys (average 7.78 seconds) than at ingroup faces (average 4.72 seconds).
  • In experiments 4 and 5, it was noted that the monkeys gazed longer at objects associated with outgroup pictures (average 3.32 seconds) than with ingroup pictures (1.6 seconds). The monkeys showed more vigilance towards anything associated with outgroups than ingroups.
  • The results from experiment 6 showed that monkeys spent less time in expected combination of pictures – outgroup with spider and ingroup with fruits. Male monkeys gave up their vigilance of the expected combination faster than they did the unexpected combinations; it was similar in the case of the female monkeys too.
  • Experiments 1 to 5 showed no differences between males and females but experiments 6 and 7 showed that females felt less negative about outgroups than males.

Next Steps/Shortcomings
The authors agree that there was a difference in the attitude in the two genders, especially in the last two experiments. They agree that this study did not address the question why there was a difference and suggest further studies to look into gender differences and their effects on intra and intergroup positive and negative biases.

This study shows that bias that is positive for intragroup individuals and negative for intergroup individuals is more deep-seated that believed earlier. The authors suggest that these biases run in primates and apes as well as humans, and go deeper than race, caste and religious differences. They conclude, “adult human intergroup attitudes are not simply the result of cultural training and experience.” They urge social researchers to look for these underlying feelings of distrust towards those who belong to different groups. Two of this study’s experiments also show that males of the species are more likely to treat outgroups with distrust, as compared to the response of the females. This can have deeper implications among human females too; it is seen in history that “men sometimes show stronger biases than women, in all cases women still do show the same types of biases as men, just to a lesser extent.” This aspect warrants further study.

For More Information:
The Evolution of Intergroup Bias: Perceptions and Attitudes in Rhesus Macaques
Journal of Personality and Social Psychology, January 2011
By Neha Mahajan; Margaret A Martinez
From the Yale University, New Haven, Connecticut

*FYI Living Lab Reports Are Summaries of the Original Research.

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