Final answer:
Franz Boas was instrumental in showing that human societies are shaped by both biological and cultural factors. He refuted the notion of cultural evolution as a linear progression and emphasized the importance of understanding each society's unique historical trajectory through cultural relativism. Boas's work also discredited race-based theories that linked physical characteristics to intellectual capacity.
Step-by-step explanation:
Franz Boas helped establish that human societies are influenced both by biology and culture. Boas, a prominent figure in the field of anthropology, is renowned for his vehement opposition to the ethnocentric and racist theories prevalent during the late 19th and early 20th centuries. He argued against the notion of cultural evolution being a linear progression towards civilization, as was the prevailing belief at the time. Instead, Boas introduced the concept that each society has a unique historical trajectory shaped by interactions and exchanges with other cultures.
Boas's work highlighted that cultural change is not structured by an overall trajectory of progress but is multifaceted, with societies adopting new ways or reviving older customs based on a web of influences including trade, migration, and conquest. His ethnographic research emphasized the cultural relativism stance, which posits that each culture should be understood on its own terms, rather than judged against those of another.
Furthermore, his research on the skull sizes of immigrants in the United States provided empirical evidence against the race-based theories of the time, showing that environmental factors could influence such physical characteristics, thereby dissociating biological differences from cultural achievements and language.