Bio-Psychological Equality
Boas argued (and did experiments to show) that biology played no role in culture.
All differences between groups are the result of their cultural-historical experiences. There are no meaningful biological differences between groups and no superior or inferior groups.
Boas wrote and spoke extensively on this topic. He had a large effect on W.E.B. Du Bois (and vice versa) and on the early NAACP. His arguments were used by the Supreme Court in Brown vs. Board of Education.