The Ethics of Science

Fisher on Human Fertility

Ronald A. Fisher, The Genetical Theory of Natural Selection, Dover, 1958.

The second section of chapter 8 begins with the following statement:

The decay and fall of civilizations, including not only the historic examples of the Graeco-Roman and Islamic civilizations, but also those of prehistoric times, which have been shown to have preceded them, offers to the sociologist a very special and definite problem---so sharply indeed that its existence appears to challenge any claim we dare make to understanding the nature and workings of human society. (Fisher 1958, 193)

In the summary part, Fisher makes quite clear in what context he raised this question:

Among the problems presented by the social evolution of Man the most conspicuous is that of the decay and ruin of all civilizations previous to our own, in spite of their having had every reason to anticipate continued success and advancement. The purely descriptive treatment of the rise and fall of civilizations is inadequate without an examination of the operative causes to which changes in social structure are due. (Fisher 1958, 206)

Towards the end of this chapter, Fisher proposes a conjecture as regards the "operative causes", and it is summarized as follows:

The specialization of reproduction in insect communities has been possible owing to the efficacy of selection in modifying fertility.. The inheritance of fertility will be seen to be equally influential, though in a very different way, in the evolution of human societies. (Fisher 1958, 206)

Thus, the topics of the following 3 chapters are set along this conjecture.

In the three following chapters we shall examine, first, the objective evidence as to the magnitude and heritability of variation in human fertility; next, we shall consider some of the widespread evidence of its association with social class; and, finally, we shall put forward a theory of the selective process by which this association appears to have been established. On this theory it may be seen that its destructive consequences are not incapable of rational control. (Fisher 1958, 205)

You may see that this "rational control" means an Eugenic policy.

In chapter 9, Fisher claims that he has shown things like this:

The number of children actually born to different individuals in civilized societies is, as in other organisms, largely influenced by chance. Whereas in most wild organisms the contribution of other causes to the actual variation is probably so small that it could not easily be detected, the total variance in the number of offspring produced in civilized man is so great that a considerable fraction must be ascribed to causes other than chance.

Temperamental qualities exert a great influence in determining celibacy, or age at marriage, both in men and women. They are, and throughout human history generally have been, at least equally important in conditioning the use or abstinence from the use of artificial methods of family limitation.

The number of children born to women is significantly correlated with the number born to their mothers. Statistics of the upper social classes in the ninteenth century suggest that about 40 percent of the total variance observed may be ascribed to heritable causes. Of these by far the most important must be inherited qualities of the mind, and especially of the moral temperament. The intensity of selection by differences of fertility, due to innate causes of the order found, is relatively enormous in comparison to selective intensities to be expected in nature. ... (Fisher 1958, 227)

Then, in chapter 10, Fisher discusses the human reproduction in relation to social class. And here are some of his conclusions:

The different occupations of man in society are distinguished economically by the differences in the rewards which they procure. Biologically they are of importance in insensibly controlling mate selection, through the influences of prevailing opinion, mutual interest, and the opportunities for social intercourse, which they afford. Social classes thus become genetically differentiated, like local varieties of a species, though the differentiation is determined, not primarily by differences from class to class in selection, but by the agencies controlling social promition or demotion.

Numerous of investigations, in which the matter is approached from different points of view, have shown, in all civilized countries for which the data are available, that the birth-rate is much higher in the poorer than in the more prosperous classes, and that this difference has been increasing in recent generations. ...

Since the birth-rate is the predominant factor in human survival in society, success in the struggle for existence is, in societies with an inverted birth-rate, the inverse of success in human endeavour. The type of man selected, as the ancestor of future generations, is he whose probability is least of winning admiration, or rewards, for useful services to the society to which he belongs.

Chapter 11 has the title "The social selection of fertility". And Fisher now begins to give his own answer to the initial question of the "decay and fall" of civilizations.

In accordance with the theory, developed with successive extensions by Galton, De Candolle, and J. A. Cobb, it is shown that the inversion of the birth-rate is a consequence of two causes which have now been fully demonstrated: (i) The inheritance of the characters, whether physical or psychological, determining reproduction; (ii) The social promotion of the less fertile. The various theories which have sought to discover in wealth a cause of infertility, have missed the point that infertility is an important cause of wealth.

In the problem of the decay of ruling classes it is shown that neither race-mixture, nor the selective action of climate and disease, would suffice to explain their failure under favourable selection. The causes to which we have traced the inversion of fertility must have been operative in the most ancient civilizations, as in our own, and serve to explain the historical importance of ruling races, through the absence of the proper attributes in the native populations. The same causes ensure an adverse selection acting upon each conquering people in turn.


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Last modified, June 6, 2003. (c) Soshichi Uchii.