The biological, physiological, or genetic classification of humans according to distinctive features of physical appearance such as skin colour, shape of face, hair colour, body morphology. It is generally used in a binary fashion to identify both a superior race and an inferior race. Throughout history, but especially since the rise of the African slave trade, the concept of race has been of concern to western political thinkers, who use it to justify and legitimate the invasive, exploitative, and predatory actions of their governments. In critical theory, race is thus treated as a problematic term whose history is instructive because it shows how power and ideology combine to facilitate the unjust and unequal treatment of others by hegemony powers. Recent scholarship in postcolonial studies has demonstrated that race is an important issue for non-western political philosophy as well. Because of its associations with colonialism, eugenics, and slavery, race has not been used in an affirmative sense in critical theory since the 1970s, when affirmative terms such as négritude began to lose their currency. It has been replaced by ethnicity in this regard.