Most people think discrimination comes from group identities—people favoring those in their own group over outsiders. But new research from the University of Sydney suggests bias can arise from something as trivial as a coin flip. The study finds that people prefer those who share even the smallest similarities with them, challenging the idea that discrimination is mainly about group loyalty.

The findings go against social identity theory, which says people divide themselves into groups and favor their own. Instead, the study suggests that even the smallest difference between two individuals can lead to favoritism.

Random discrimination

The researchers ran seven experiments with over 1,400 participants in the United Kingdom. They asked people to make arbitrary choices—such as picking a favorite painting (by Kandinsky or Klee), estimating the number of dots in a cloud, or flipping a coin. Participants were then given money to distribute, knowing only whether the recipient had made the same choice or had the same coin flip result.

The results were striking. On average, people gave 43.1% more money to those who shared their preference or random outcome. Even a coin flip—a meaningless event—was enough to trigger bias. This suggests that discrimination isn’t just about group identity but can stem from individual instincts.

The findings have troubling implications. If people treat others differently based on something as random as a coin toss, bias may be more widespread and harder to prevent than we assume. Earlier research showed that people discriminate based on real differences, such as political or religious views. This study suggests that even trivial differences can shape behavior.

Neurological detection

Why does this happen? One possibility comes from neuroscience: the brain detects differences as a kind of conflict, which triggers negative emotions. Recognizing similarity, on the other hand, may create positive emotions and lead to favoritism.

The researchers warn against jumping to conclusions about how to fight discrimination. “Because these are basic scientific results, their implications for interventions designed to prevent discrimination are highly speculative,” they note. But if bias can emerge from something as small as a coin flip, solving it may be harder than we thought.