BIOLOGICAL FOUNDATIONS OF SOCIOLOGY 537
tion of the unfit is reduced to a minimum, it tends to degenerate. Thus we cannot improve or even preserve our breed of race- horses merely by supplying good food and the other conditions necessary for a healthy existence. We must weed out the unfit, and so breed the race with care.
Were the prevailing medical doctrine, that variations are nor- mally caused by the direct action of the environment on the germ- plasm, true, all life would be impossible on earth; for all living species are subjected to deteriorating influences, such as cold, want, and disease. Unless the germ-plasm were resistant to the environment, every species would drift steadily and helplessly to destruction. Natural selection could not preserve it. There could be no selection when all variations were unfavorable. There could be no improvement in a race when in each generation all its indi- viduals were inferior to their predecessors. Medical men found their belief chiefly on certain statistics, compiled mainly by gentle- men in charge of lunatic asylums, which demonstrate that a large number of feeble-minded people have parents or grandparents dis- eased or intemperate. But these statistics fail to take into account the proportion of cases which have inherited parental defects, or which have varied spontaneously from the parents. They fail also to demonstrate that asylum patients have parents diseased or intemperate in a greater proportion of cases than people of the same social stratum outside the walls. I hope it will be under- stood that, in controverting the prevailing medical doctrine, I do not mean to imply that variations in offspring are never caused by parental disease or intemperance. I mean to imply merely that instances of variations so caused must be very rare. Other- wise the race would become extinct. We know that the offspring of diseased and intemperate people are often perfectly normal and robust. That implies that their germ-plasm was insusceptible to the action of toxins and alcohol. This insusceptible type survives. The susceptible types are weeded out. A high degree of insus- ceptibility is thus established as a necessary condition of individual and racial survival, and in the process of ages becomes almost absolute. Doubtless the germ-plasm of every species is most insusceptible to the influences to which it is normally exposed.
