Physical anthropology has its roots in the Enlightenment, but became acknowledged as a distinct scientific discipline in the second half of the nineteenth century. Its aim was to examine human evolutionary history, and to describe and interpret the biological diversity found among people. For this purpose, anthropologists developed a range of instruments, measuring methods, and statistical techniques. They focused on a variety of external physical characteristics, such as skull shape; anatomical measurements; and eye, hair, and skin color.
Anthropologists believed they could sort humanity into a well-defined system of racial groupings. It was common to assume that human races were something that existed in nature, and that these races were something that science could “detect,” analyze, and define. Nonetheless, researchers never agreed on how many human races existed. Their number might range from three or four to dozens.