Few anthropologists and biologists, in the 1st half of the 20th Century, believed that it was difficult to use zoological nomenclature for classifying humans into groups. According to them, classifying humans into races, was not a creative endeavor to examine human variation. Anthropologist Ashley Montagu and biologist Julian Huxley were two significant opponents of using the term 'race'. They noted, there were no clear boundaries in the continuous stream of human variation. They suggested that human variation and relationships among human groups must be studied using Darwinian natural selection and concepts such as mutation, isolation, random genetic drift, endogamy, etc.
Following Huxley, Deniker, and Huddon, Montagu adopted the term 'ethnic group' as a replacement for 'race' in 1942.
Following World War 2, UNESCO issued a statement suggesting to replace the term 'race' with 'ethnic group', including both; scientific opposition to race theories, and a moral condemnation of racism.
During this time, some anthropologists suggested that population should be the basic unit of study of human diversity, and adaptation subjected to specific environmental constraints.
As these populations adapted to these particular environments, they came to manifest traits that were unique. Thus, races could be viewed as episodes in the evolutionary process. (Hulse, 1962)
Despite the paradigm shift in the construct of race, the racist view of humanity has not changed, even in the 21st century. The outcome of which is, ethnic violence, warfare, terrorism, and genocide.
Reference: IGNOU study materials