Us and Them: Understanding Your Tribal Mind is a 2005 nonfiction book by David Berreby about how humans divide and categorize themselves. The psychological text explains human nature and the neuroscience of human groupings like races, ethnicities, classes, and nationalities. Berreby also discusses the positive and negative effects of human-kind groupings and offers advice on how to better act on human-kind beliefs.

Plot Summary

Berreby begins by explaining the concept of human kinds—a number of people that is more than one but fewer than everyone. He describes human-kind categories we are born into, such as family and race; perceived human-kind categories, like being a nerd or punk; and acquired categories, like attorney or millionaire. Berreby explains the function of human-kind beliefs: They guide people through the world. He elaborates on how they work.

Berreby explains faulty pseudoscience that forms the basis of harmful human-kind beliefs like stereotypes. Science offers theories, but humans crave certainty and confirmation of preconceived biases. We are adept at manipulating scientific data to apply certainty to our faulty beliefs. This habit leads to stereotypes, which are inaccurate and erroneous human-kind beliefs. Berreby explores other methods of tricking minds into forming false human-kind beliefs, such as invention of tradition and founder effects. He details how, once grouped into a human kind, members can further define the group through looping effects: The group’s definition shapes its members’ behavior, and their actions affect the group’s definition.

Humans are the only animals able to interpret human-kind codes because we are the only animals able to view objects as symbols. We perceive objects both as what they are and as indicators of nonphysical facts. This process occurs when the real world meets our minds. We have complex mental circuits which span our entire brain, constantly receiving, summarizing, and transmitting electrical signals to interpret these codes. Humans are born able to learn this. If presented with the appropriate stimulus, our minds figure out the rest.

The ability to interpret and transmit codes enables us to build large societies and dominate the Earth. Humans create societal rules through shared culture. Human-kind groups allow us to communicate via symbols and signs that people share, and therefore, play by the same rules. Once we establish someone as in our human-kind group, we trust we can exchange goods, ideas, and emotions with them—even if they are strangers. Inclusion is a good thing, but exclusion has negative effects. We see those who don’t share our culture as “not our kind” and don’t allow them to participate in our society. Sometimes, people enforce this “Us-Them” relationship through stigma. Stigmatized groups suffer psychologically and physically.

While human-kind beliefs can produce harmful results when people act on them, such as stereotypes and stigma, they are also a valuable human trait that allow our species to evolve and achieve remarkable things. Human-kind beliefs and the neurological codes that form them are beneficial to humanity, but we must become more knowledgeable of how they function to prevent pseudoscience, external manipulation, or subconscious biases from shaping human-kind beliefs and influencing harmful action.