"It is better for all the world if instead of waiting to execute degenerate offspring for crime, or let them starve for their imbecility, society can prevent those who are manifestly unfit from continuing their kind. . . . . . Three generations of imbeciles is enough (Buck v. Bell, 1927)."
"Most of those who have sought to suppress human knowledge about heredity have done so with kindly intentions, but sound policies can never be constructed on bad science or unsound data. Any society that sets itself against the immutable causal laws of biology and evolution will ultimately bring about its own demise" (Pearson, p. 140)."
"the various races, when carefully compared and measured, differ much from each other - as in the texture of hair, the relative proportions of all parts of the body, the capacity of the lungs, the form and capacity of the skull, and even the convolutions of the brain. But it would be an endless task to specify the numerous points of difference. The races differ also in constitution, in acclimatization and in liability to certain diseases. Their mental characteristics are likewise very distinct; chiefly as it would appear in their emotion, but partly in their intellectual faculties. Everyone who has had the opportunity of comparison, must have been struck by the contrast between taciturn, even morose aborigines of S. America and the light-hearted talkative negroes (p. 20)."
See
http://www.eugenics.net/papers/gw001.html