Us and Them: Neurobiology of Intergroup Differences and Conflict

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Image by John Hain from Pixabay

Written by Brett Weiss

December 2019

Biology reveals that humans are animals– Old World primates, also referred to as apes (Sapolsky, 2018).  Humans have innate needs and desires to belong to groups, and with these needs comes potential for differences and conflict between groups.  Countless examples throughout human history reveal the dangers of these differences: from wars to genocides and from prejudice to stereotypes.  One might ask, “How do we compare behaviorally to other Old-World ape species?”  How has the human brain evolved in comparison to chimpanzees or baboons for instance to make us uniquely human?

Male chimpanzees form territorial ‘border patrols’ to stop other groups of their species from breaching territorial lines.  If an opposing male chimpanzee breaches the demarcation, a male from the other group may murder him (Sapolsky, 2018).  Chimpanzees, along with many other species, form groups based on olfaction (sense of smell).  They can distinguish who relates to them closest based on odor, which helps them to form groups based on kinship.  Kinship entails sharing genetic compositions with others so that one’s genes may pass to the next generation.  Through evolution, humans lost this ability to determine kinship based on odors; and instead, humans use reason.  For instance, a human might remember who a sibling, cousin, aunt, uncle, or parent may be.  This helps humans to determine whom they need to defend based on kinship.  Thus, as the adage goes, “I’ll gladly lay down my life for two brothers or eight cousins.”  Using reason and memory to determine kinship constitutes a uniquely human attribute, which results in feeling more related to others based on identity.  Humans frequently use memory and reason for “pseudo-kinship,” resulting in Christian brotherhoods, sororities, parental figures, etc. (Sapolsky, 2018).  “Pseudo-kinship” allows for people to band together for shared religion, nationality, or sports team partisanship, which represents an unprecedented phenomenon throughout the rest of the animal kingdom (Sapolsky, 2018).

Research in social neuroscience has only begun to uncover details related to group formation in humans.  Much of the research relates to the notion of representing “us” and “them,” or social categorization more specifically.  The research has focused on static groups and categories, such as race, which has made making inferences on the underlying processes involved difficult to generalize.  Across experiments from these studies, differences in social context and experimental methods have produced inconsistent results.  This has led to research on creating an “us” and “them” scenario in the laboratory using a ‘minimal group’ paradigm.  In this paradigm, people are told that they have been assigned to a particular group based on arbitrary group differences, such as taste for abstract art or dot estimation abilities.  Once assigned to groups, participants typically have no face-to-face contact within or between groups.  Remarkably, under these circumstances, participants regularly apply discrimination in favor of their in-group members (Cikara & Van Bavel, 2014).  This highlights how readily people identify with social groups along with the context-dependent nature of group formation.

Once groups form, intergroup differences often entail prejudice and stereotyping.  Prejudice refers to preconceptions or attitudes about groups, races, or ethnicities and associates with emotions such as fear or disgust.  Stereotypes involve cognizing characteristics given to a social group, such as ‘unintelligent’ or ‘poor (Amodio, 2014).’  The neural basis of prejudice encompasses a network of various brain regions.  The amygdala, a structure located bilaterally toward both lower sides of the brain, processes early threat such as an out-group member’s face.  The insula, located bilaterally toward the side of the brain, processes emotion associated with the target, such as an out-group member’s face, and supports emotional responses such as disgust for the out-group member.  The striatum, a structure located bilaterally above the amygdala, orchestrates a behavioral response.  The orbital frontal cortex, located toward the front of the brain above the eyeballs, gives emotion-related judgments of social outgroup members, which affects activity in the medial prefrontal cortex, a region above the orbital frontal cortex.  The medial prefrontal cortex generates empathy and mentalizing, and a negative assessment from the orbital frontal cortex facilitates decreased activity in this region (Amodio, 2014).  The ‘prejudice network’ of brain regions acts in concert to produce an experience of prejudice in humans.

Stereotyping also has a neural network in humans.  The stereotyping network includes the anterior temporal lobe, a region of both sides of the brain, which stores social information such as stereotype-related knowledge of people and social groups.  The information from the anterior temporal lobe then relays to the dorsal prefrontal cortex, a region toward the front of the brain, for the formation of ‘impressions’ or ‘stereotypes.’  The ‘impressions’ or ‘stereotypes’ then relay to the inferior frontal gyrus, toward the front of the brain, to support goal-oriented actions related to the ‘stereotypes (Amodio, 2014).’

The observation that groups form and that conflicts arise between groups of humans seems indisputable.  Some researchers have proposed methods for alleviating intergroup differences and conflict.  These methods range from utilizing oxytocin, a hormone involved in social bond formation, to banishing testosterone in humans (Sapolsky, 2018).  Essentially, though, each remedy that researchers have proposed to alleviate intergroup tensions has the potential to backfire and make intergroup differences worse.  For instance, oxytocin has shown to increase social bond formation toward in-group members but could actually exacerbate out-group hostility (Sapolsky, 2018).  According to Dr. Robert Sapolsky of Stanford, an expert in primate behavior, no easy remedy exists yet to alleviate intergroup conflict.  That which may constitute behavior that some see as humans at their worst may seem like humans at their best to others (Sapolsky, 2018). 


Amodio DM (2014).  “The neuroscience of prejudice and stereotyping.”  Nat Rev Neurosci.  15(10): 670-682.

Cikara M & Van Bavel JJ (2014).  “The Neuroscience of Intergroup Relations: An Integrative Review.”  Perspect Psychol Sci.  9(3): 245-274.

Sapolsky RM (2018).  “Doubled-Edged Swords in the Biology of Conflict.”  Front Psychol.  9: 2625. 

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