Such theories have provided ideological justifications to racism, slavery and colonialism during the New Imperialism period in the second half of the 19th century. Their popularity coincide with this period of European expansion in the world.
Rather than being based solely in objective observation, scientific racism is a scientific tradition in which biology is used not only to prove the existence of race, but also, to maintain existing social hierarchies.
The philosophical and political underpinnings of ideas associated with racial superiority and inferiority were first given scientific legitimacy and credence with the publication of Charles Darwin's (1859) revolutionary book, The Origin of Species.
The "science" of phrenology purported to demonstrate that the structure of the skull, especially the jaw formation and facial angles, revealed the position of various races on the evolutionary scale, and a debate raged on whether there had been one creation for all mankind (monogenism) or several (polygenism).
By the 1920s, scientific racism was already facing intellectual resistance, perhaps most insistently from Catholics such as Hilaire Belloc, and its later association with Nazism eventually brought about its near complete demise.
Aspirations to develop a homogenous "race" of people were based on the premise that there once existed a "pure race." It was accepted that "in the beginning" people were divided regionally and each region shared similar characteristics and phenotypes.
In South Africa, the triumph of apartheid in the 1950s gave a new lease on life to racial ideologies that after the defeat of Nazism were discredited elsewhere
Despite Charles Darwin's idea that there were no fixed divisions between species, let alone races, polygenist notions of race, which assumed that the divisions between races were ancient and fixed, thrived in the new evolutionary thought.
Today, the phrase is used either as an accusation or to describe what is generally considered to be historical racist propaganda about the supposed existence of different "human races", refuted by The Race Question UNESCO statement who advocated the use of the more precise term "ethnic group".
Everything from craniometry to phrenology to I. Q. tests were used by scientists to prove the inferiority of non-white races. Scientists obtained their ideas on race from society; they then proved these ideas using scientific "facts;"