 If the apogee of biological race was reached in the early twentieth century, its decline began at about the same time. While writers such as Chamberlain and Grant popularized and politicized biological conceptions of race hierarchy, academic anthropologists since Blumenbach gave the concept of race its scientific validity. But academic anthropology also provided the first challenge to biological race in the person of Columbia University professor Franz Boas (1858–1942), a German-born Jewish immigrant to the United States. Boas challenged the fixed character of racial groups by taking on one of the key fundaments to racial typology, cranium size. Boas showed that this characteristic was profoundly affected by environmental factors, noting that American-born members of various “racial” types, such as Semitic Jews, tended to have larger crania than their European-born parents, a result of differences in nourishment. From this he concluded that claims about racially differential mental capacities could similarly be reduced to such environmental factors. In so doing, Boas undermined one measure of racial distinction, and although he did not go so far as to reject entirely the concept of biological race itself, he strongly influenced anthropologists to shift their focus from putatively fixed biological characteristics to apparently mutable cultural factors in order to understand differences among human groups (Bernasconi and Lott 2000, 84–88; Brace 2005, 167–169; Cornell and Hartmann 1998, 42–43).