While humans do not come with a ready-made way to create divisions of humanity, we have the capacity to classify and develop mental shortcuts to use classifications once we have created (or learned) them. Most importantly, categories like “us” and “them” are not set in stone; they are flexible and do not necessarily set up a conflictual relationship.
Neuroscientists recently reviewed a wide range of data on how the brain works when we categorize people into groups. They found that the biological bases of the classification processes show that specific in-group and out-group categories are not “hard-wired.” Rather, our neurobiology reflects a highly flexible system that can represent the self and others. Additionally, how “us” and “them” are divided can shift quickly and dynamically. This is a very different reality from the assumption of a natural, inherent “us vs. them” mentality.
Even the argument that the “us vs. them” mode of existence came into being with the evolutionarily recent advent of agriculture, cities, states, and nations is not correct. Humans are neither Hobbesian beasts nor Rousseauian egalitarians; we are a species that is characterized by between-group relations that are complex and dynamic, good and bad.