before the 2th century, scientists generally believed that human beings were divided into several races by essentialism (that is, by indispensable characteristics), such as Negro race (black race), Mongolian race (yellow race) and Caucasian race (white race). But since the 194s, evolutionary scientists have begun to eliminate this theory.
In addition, race has long been understood as a scientific classification, that is, race is regarded as a level of classification, such as equating race with subspecies; However, since 196s, new data and models in population genetics research have made some scientists begin to question this understanding, and turn to other concepts such as population, cline (also translated as "gradual group" or "ecological group") to study the differences within human beings.