BIOLOGICAL FOUNDATIONS OF SOCIOLOGY 539
in the environment. Thus it is only because children vary spon- taneously from their parents in all directions, like bullet marks round a bull's-eye, that natural selection has been able to render the races of mankind resistant to all the diseases by which they are assailed.
We reach thus two fundamental biological laws. The first law is that the germ-plasm is very highly indifferent to the action of the environment, and therefore that children are seldom affected by the influences to which their parents are exposed. The second law is that germ-cells, and therefore the individuals that arise from them, vary spontaneously among themselves, just as the body-cells vary, and for the same reason. It follows that we cannot improve races of plants and animals by improving the con- ditions under which they exist. Such a course benefits the indi- vidual, but results in racial degeneration. The race can be improved only by restricting parentage to the finest individuals. All the practice, if not the theory, of breeders confirms us in this belief.
It will be well worth our while to devote a little space to a consideration of some of the effects resulting from man's evolu- tion against disease. Probably this evolution is the only form of evolution which civilized races are now undergoing. Such is our care for the weak in body and mind that there is nothing to indi- cate, for example, that big and strong and active men, or clever men, have, on the average,, more children than smaller or duller men. Nearly all our deaths are due to disease or old age. The few that are otherwise caused are not selective in the sense that they eliminate particular types of individual. Thus death by drowning does not select particular types. It falls on the fit and unfit in a fashion that is quite haphazard.
Zymotic diseases that is, diseases due to living microbes appear to have originated among the ancient and crowded popu- lations of the Old World. Our oldest histories, even our oldest myths, tell of plague and pestilence. But we have no indication, with the exception of malaria, that any such diseases existed in the Western Hemisphere before the arrival of Europeans. On the contrary, while we never hear of European adventurers in the
