Final answer:
The assertion is true; physical anthropologists have revealed that racial categories are not scientifically valid due to significant genetic variation within categories and overlapping traits amongst all humans. Social constructions of race have been arbitrary and shaped by historical prejudices. Emphasizing ancestry offers a more accurate understanding of human genetic diversity than race.
Step-by-step explanation:
The statement that physical anthropologists have shown that the assumed clear and distinct differences among races are not clear or distinct at all is true. Biological anthropology demonstrates that racial categories are not biologically justifiable as there is more genetic variation within these categories than between them. Traits like skin color, facial features, hair texture, and blood type exist along spectrums, effectively dispelling the notion of discrete racial categories.
Social science organizations, including the American Association of Anthropologists and the American Sociological Association, reject biological explanations of race, emphasizing the social construction of race. This perspective suggests that categories of race have been arbitrarily assigned and historically used to justify racist practices. Furthermore, statistics reinforce this view, with genetic variation within so-called racial groups being equal to or greater than that between different groups. After sequencing the human genome, many scientists argue against using race in genetic research, due to the vast genetic diversity within any given racial category. Instead, focusing on ancestry could facilitate a greater understanding of human genetic diversity, which is more meaningful than race.