ABSTRACT
In nature, animals are essentially prisoners of the type of environment in which they have evolved and to which they are adapted. But the human species, as has been noted, has spread over the entire globe. The mutations which have brought about the different races have never been sufficiently profound to prevent any human group from adapting to any of the environmental conditions under which other human beings find it possible to live. As is the case for all living species, mutations continuously occur in the human species, and those mutations which have been selected by the environmental conditions and by the ways of life have produced the diversity of biological types which people call races. Humanity constitutes a highly integrated and complex system of an immense number of genetic and social forces. Any profound change in its genetic endowment would destroy this integration and probably soon spell the end of human life.
