Final answer:
Key anthropologists at the start of the 20th century include Franz Boas's students Ruth Benedict, Margaret Mead, and Edward Sapir, who made significant contributions to the field of psychological anthropology and were pivotal in shaping the discipline.
Step-by-step explanation:
The main anthropologists of the early twentieth century and the second generation include the students of Franz Boas. Ruth Benedict, Margaret Mead, and Edward Sapir are among the prominent figures who continued Boas's work. These anthropologists each took their research in unique directions, with Benedict focusing on cultural personality studies, Mead on child-rearing practices and adolescence, and Sapir on the intersection of psychology and language. Together, they laid the groundwork for the subfield of psychological anthropology. Their work was essential in building upon the concepts initiated by earlier scholars such as W. H. R. Rivers, a British psychiatrist and anthropologist known for his research on the inheritance of sensory capabilities and disabilities among Melanesian populations.