Racial classification systems focused on presumed objective physical characteristics, but the systems were not neutral. The races were ordered in specific hierarchies. Some races were placed at a higher evolutionary level than others, considered more intelligent, stronger, or healthier. Such “scientific” assumptions helped to legitimize inequality, racism, and exploitation. The explicit premise was that a white European elite should rule over racially “primitive” colonized peoples and those lower social classes often perceived as biologically inferior.

These ideas were explicitly expressed within the eugenics or racial-hygiene movement and reached their greatest extreme in Nazi Germany. However, both racial hygiene and similar Nazi racial policies were inspired all around the world by mainstream science, and were met with both criticism and support in scientific circles.