We are all mammals, and our brains carry an evolutionary history that can sometimes make unfamiliar people or situations feel more threatening or uncertain than they actually are. Our brains evolved to help us detect potential danger, navigate social relationships and respond quickly to our environment. Although the human brain has continued to evolve, many of the systems involved in emotion, threat detection and social behaviour have much deeper evolutionary roots than modern societies do. And this matters when we think about difference.

One of the most consequential ideas developed in European intellectual history was the classification of human beings into racial categories. Race was constructed as a way of categorising people, often based on perceived physical differences, and these categories were subsequently used to create hierarchies and justify systems of power and exclusion. The consequences have been profound, including the distortion and marginalisation of African histories and the creation of assumptions about human difference that have persisted across societies. Scientifically, however, we are one species: Homo sapiens. Our species evolved in Africa, with the oldest currently recognised Homo sapiens fossils dating to around 300,000 years ago. All living human beings share this common evolutionary history, and our genomes are more than 99.9% alike.

There is enormous human variation, including differences in skin colour, physical characteristics and genetic ancestry. Yet those differences exist within a single human species, and most genetic variation occurs within populations rather than neatly between socially defined racial groups. Perhaps the more useful question, therefore, is not why humans are different. It is why we have historically attached so much social meaning, hierarchy and value to those differences.