Identifying human races in terms of skin color, at least as one among several physiological characteristics, has been common since antiquity. Such divisions appeared in rabbinical literature and in early modern scholarship, usually dividing humankind into four or five categories, with color-based labels: red, yellow, black, white, and sometimes brown. It was long recognized that the number of categories is arbitrary and subjective, and different ethnic groups were placed in different categories at different points in time. François Bernier (1684) doubted the validity of using skin color as a racial characteristic, and Charles Darwin (1871) emphasized the gradual differences between categories. Today there is broad agreement among scientists that typological conceptions of race have no scientific basis.