What was the scientific reason Europeans gave to justify imperialism in Africa?

There was the idea of social darwinism and also of biological and scientific racism

The idea was that the strong have the right to rule over the weak in the similar manner in which the evolutionary species are sometimes on the top of the food chain and sometimes on the bottom. This was combined with the idea that some races are inherently lower races based on their race which was a pseudoscientific fake belief that was used as justification for colonialism.