Sense 1a of this entry describes the word race as it is most frequently used: to refer to the various groups that humans are often divided into based on physical traits, these traits being regarded as common among people of a shared ancestry. This use of race dates to the late 18th century, and was for many years applied in scientific fields such as physical anthropology, with race differentiation being based on such qualities as skin color, hair form, head shape, and particular sets of cranial dimensions. Advances in the field of genetics in the late 20th century determined no biological basis for races in this sense of the word, as all humans alive today share 99.99% of their genetic material. For this reason, the concept of distinct human races today has little scientific standing, and is instead understood as primarily a sociological designation, identifying a group sharing some outward physical characteristics and some commonalities of culture and history.