Franz Boas

Was racist after all.
Often, however, the discrepancies remain unknown. They develop too gradually for the average person to notice and are most obvious to those who least want to point them out, i.e., the successors of the great teacher. Of course, the great teacher is no longer around to set things straight.
This has happened to many belief-systems. In my last post, I discussed how the real Sigmund Freud differed significantly from the one we know. The same is true for Franz Boas (1858-1942), whose school of anthropology is as much a product of his immediate disciples—Margaret Mead and Ruth Benedict—as of Boas himself.
Today, Boas is remembered as the man who moved the social sciences away from genetic determinism and toward environmental determinism. His Wikipedia entry states:
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. [...] 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.
In reality, he felt that genes do contribute substantially to mental and behavioral differences ... and not just between individuals. This is apparent in a speech he gave in 1894 under the title "Human Faculty as Determined by Race."
It does not seem probable that the minds of races which show variations in their anatomical structure should act in exactly the same manner. Differences of structure must be accompanied by differences of function, physiological as well as psychological; and, as we found clear evidence of difference in structure between the races, so we must anticipate that differences in mental characteristics will be found.  [...] As all structural differences are quantitative, we must expect to find mental differences to be of the same description, and as we found the variations in structure to overlap, so that many forms are common to individuals of all races, so we may expect that many individuals will not differ in regard to their faculty, while a statistical inquiry embracing the whole races would reveal certain differences. Furthermore, as certain anatomical traits are found to be hereditary in certain families and hence in tribes and perhaps even in peoples, in the same manner mental traits characterize certain families and may prevail among tribes. It seems, however, an impossible undertaking to separate in a satisfactory manner the social and the hereditary features. Galton's attempt to establish the laws of hereditary genius points out a way of treatment for these questions which will prove useful in so far as it opens a method of determining the influence of heredity upon mental qualities (Boas, 1974, p. 239)
We have shown that the anatomical evidence is such, that we may expect to find the races not equally gifted. While we have no right to consider one more ape-like than the other, the differences are such that some have probably greater mental vigor than others. The variations are, however, such that we may expect many individuals of all races to be equally gifted, while the number of men and women of higher ability will differ. (Boas, 1974, p. 242) 
 When discussing brain size, Boaz merely pointed to the overlap among racial groups:
We find that 50 per cent of all whites have a capacity of the skull greater than 1550 cc., while 27 per cent of the negroes and 32 per cent of the Melanesians have capacities above this value. We might, therefore, anticipate a lack of men of high genius, but should not anticipate any great lack of faculty among the great mass of negroes living among whites and enjoying the advantages of the leadership of the best men of that race. (Boas, 1974, pp. 233-234)
He did add that "mental ability certainly does not depend upon the size of the brain alone." He then argued, quoting an authority, that the encephalon and the cortex develop to a greater degree in whites, especially after puberty:
When we compare the capacity for education between the lower and higher races, we find that the great point of divergence is at adolescence and the inference is fairly good that we shall not find in the brains of the lower races the post-pubertal growth in the cortex to which I have just alluded. (Boas, 1974, p. 234)