in intellectual traits may involve the dynamic deficiencies which common opinion claims to exist."
There are other racial and heritable differences of much importance, which are given too little recognition—namely, the differences of disease resistance. Here one can speak unhesitatingly of a real inferiority in respect to the environment of North America.
As was pointed out in the chapter on Natural Selection, the Negro has been subjected to lethal selection for centuries by the Negro diseases, the diseases of tropical Africa, of which malaria and yellow fever are the most conspicuous examples. The Negro is strongly resistant to these and can live where the white man dies. The white man, on the other hand, has his own diseases, of which tuberculosis is an excellent example. Compared with the Negro, he is relatively resistant to phthisis and will survive where the Negro dies.
When the two races are living side by side, it is obvious that each is proving a menace to the other, by acting as a disseminator of infection. The white man kills the Negro with tuberculosis and typhoid fever. In North America the Negro can not kill the white man with malaria or yellow fever, to any great extent, because these diseases do not flourish here. But the Negro has brought some other diseases here and given them to the white race; elephantiasis is one example, but the most conspicuous is hookworm, the extent and seriousness of which have only recently been realized.
In the New England states the average expectation of life, at birth, is 50.6 years for native white males, 34.1 years for Negro males. For native white females it is 54.2 years and for Negro females 37.7 years, according to the Bureau of the Census (1916). These very considerable differences can not be wholly explained away by