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 the fact that the Negro is crowded into parts of the cities where the sanitation is worst. They indicate that the Negro is out of his environment. In tropical Africa, to which the Negro is adapted by many centuries of natural selection, his expectation of life might be much longer than that of the white man. In the United States he is much less "fit," in the Darwinian sense. In rural districts of the South, according to C. W. Stiles, the annual typhoid death rate per 100,000 population is: _Whites_ _Negroes_ Males 37.4 75.3 Females 27.4 56.3 These figures again show, not alone the greater intelligence of the white in matters of hygiene, but probably also the greater inherent resistance of the white to a disease which has been attacking him for many centuries. Biologically, North America is a white man's country, not a Negro's country, and those who are considering the Negro problem must remember that natural selection has not ceased acting on man. From the foregoing different kinds of evidence, we feel justified in concluding that the Negro race differs greatly from the white race, mentally as well as physically, and that in many respects it may be said to be inferior, when tested by the requirements of modern civilization and progress, with particular reference to North America. We return now to the question of intermarriage. What is to be expected from the union of these diverse streams of descent? The best answer would be to study and measure the mulattoes and their posterity, in as many ways as possible. No one has ever done this. It is the custom to make no distinction whatever between mulatto and Negro, in the United States, and thus the whole problem is beclouded.