Does Natural Selection Continue to Operate in Modern Mankind?

Abstract

THE purpose of the present article is to examine the validity of the assertion, frequently made in medical, biological and sociological writings, that natural selection has been relaxed or even done away with altogether in modern mankind, particularly in advanced industrial societies. With this assertion as a premise, dire predictions of biological decadence of the human species have been uttered, especially in popular scientific literature. It is of course not our intention in this article to grapple with this immense problem in its entirety, and we mean neither to affirm nor to refute the predictions of decadence. We feel, however, that the thinking in this field may gain in clarity from a re-examination of the concepts of natural selection and adaptation, particularly as they apply to man. Such a re-examination is the more needed since these concepts have not remained stable even in biology since they were advanced by Darwin. Particularly rapid change has taken place in recent years in connection with the development of population genetics. Natural selection is regarded in modern biology as the directing agent of organic evolution. The process of mutation yields the genetic variants which are the raw materials of evolutionary change. Sexual reproduction then gives rise to innumerable gene combinations or genotypes. However, which mutants arise, and when, has nothing to do with their possible usefulness or harmfulness to the species. Natural selection, nevertheless, so maneuvers the genetic variability that living species become fitted to their habitats and to their modes of life. Organic evolution consists of a succession of threatened losses and recapturings of the adaptedness of living matter to its environment. But the environment does not change the genotype of a living species directly, as some evolutionists of the past have wrongly assumed. The role of the environment consists rather in that it constantly presents challenges to the species; to these challenges the species may respond either by adaptive modification or by extinction. It would be an exaggeration to say that the above view of the evolutionary process is universally accepted. Few biological theories really are. However, the importance of natural selection, at least as an agent which guards against degenerative changes in populations, is denied by scarcely anyone. We need not labor the point that the evolution of the ancestors of the human species was brought about by the operation of the same fundamental biological processes which act elsewhere in the living world. A new situation has arisen with the advent of the human phase. Species other than man become adapted