 Boas was one of the most prominent opponents of the then-popular ideologies of scientific racism, the idea that race is a biological concept and that human behavior is best understood through the typology of biological characteristics.In a series of groundbreaking studies of skeletal anatomy he showed that cranial shape and size was highly malleable depending on environmental factors such as health and nutrition, in contrast to the claims by racial anthropologists of the day that held head shape to be a stable racial trait.Boas also worked to demonstrate that differences in human behavior are not primarily determined by innate biological dispositions but are largely the result of cultural differences acquired through social learning.