Natural selection in human populations : the measurement of ongoing genetic evolution in contemporary societies / edited Carl Jay Bajema.

Date:
[1971]
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Natural selection in human populations : the measurement of ongoing genetic evolution in contemporary societies / edited Carl Jay Bajema. Source: Wellcome Collection.

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    6 NATURAL SELECTION IN HUMAN POPULATION caution. What, indeed, is selection, and when is a selection natural and when is it not? Darwin said that natural selection is the outcome of the survival of the fittest in the struggle for life. Struggle suggests strife, contention, competition. Darwin himself wrote that ... from the war of nature, from famine and death, the most exalted object we are capable of conceiving, the higher animal, directly follows. However, natural selection does not ineluctably depend on any of these things. Birch (1957) has defined competition thus: Competition occurs when a number of animals (of the same or different species) utilize common resources the supply of which is short; or if the resources are not in short supply, competition occurs when the animals seeking these resources nevertheless harm each other in the process. Natural selection may, however, take place when resources are not limiting, if the carriers of some genes possess greater reproductive potentials than others. Some cases have been observed in experiments with animals and plants when a genotype superior under competition is inferior in the absence of competition, or vice versa. And who is the fittest, whose survival results in natural selection? Does na¬ tural selection make us fit for life in the society of other men, or for wisdom, or for good will, or for unselfishness? It does not necessarily ordain any of these qualities. Darwinian fitness is a measure of the reproductive proficiency. Its guiding principle is be fruitful, and multiply, and replenish the earth. It is quite indispensable to distinguish Darwinian fitness from excellence in human estimation. The two may go hand in iiand, but sometimes they may be in opposition. It is man and man alone who can probe, scrutinize, and question the wisdom of the evolutionary process which brought him into being. He may improve what na¬ ture hath wrought. When man chooses the individuals who are to become parents of the succeeding generation he practices artificial selection. According to Lerner (1958), artificial selection is a process which has a goal that can be visualized. Any selection which is not artificial is natural selection. Mutation and the Normalizing Natural Selection There are several forms of natural selection operating in the human species, as well as in other organisms. Although the distin(;tions between these forms of selec¬ tion are neither absolutely rigid nor always clear-cut, they are helpful for straight thinking about evolutionary problems. Stabilizing (Schmalhausen 1949) or normal¬ izing (Waddington 1957) natural selection is the simplest and most obvious. It is a conservative force; it counteracts the spread in populations of detrimental mutants, hereditary diseases, and weaknesses of various kinds. Failure, or at least relaxation, of the normalizing selection in human populations leads to fears that an insidious process of genetic decay is at work in the human species. Is there a basis for these fears? Mutations continue to arise in man, even as they have been arising since the