Racist theory behind "they all look the same"?

It's called CRR for cross racial recognition. It works both ways. Whites have trouble distinguishing between other races and visa versa.

Race is socially constructed for power, privilege, rights. What do you mean by "they all look the same"? If you look across all different ethnicities, humans have very little variation within their regional background. Most chinese will have similar appearances, so did scandinavians, and aboriginals. There is no such thing as as "inferior races" because depending on your background, you may come from a huge ethnic population or very little. It depends on the number of people, and whether these groups outmarried other ethnicities and whether they had contacts with other people. Do you mean that white people have varying eye colors/hair and not Asians, African Americans, Mexicans, and Iranians? This is only color variation and is the result of color pigment from living in colder climate areas for thousands of years. HOwever, all humans have the same genetic make-up.

I would have to argue that it is not always racist. If a person is used to looking at people of African decent, for example, because he comes from a village in Kenya and has never saw a Chinese person before he will naturally come to the conclusion that all Chinese people look alike. The human brain looks for patterns and with experience will learn ways of distinguishing between faces etc and therefore living in Kenya he will be more used to differentiating between Kenyan faces. Another factor is the fact that some societies do indeed have less obvious distinguishing features. White people for example can have red, blonde, brown or black hair whereas black people only have black hair same thing goes for eye colour.

There’s no scientific theory for that, only pseudo-scientific ones that are outdated now. As S.H. rightly said, we now know them as stereotypes!

it's called a stereotype