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“Data for the Problem of Evolution in Man. V. On the Correlation between Duration of Life and the Number of Offspring”
Published online by Cambridge University Press: 18 August 2016
Extract
According to the Darwinian theory of evolution the members of a community less fitted to their environment are removed by death. But this process of natural selection would not permanently modify a race, if the members thus removed were able before death to propagate their species in average numbers. It then becomes an important question to ascertain how far duration of life is related to fertility. In the case of many insects death can interfere only with their single chance of offspring; they live or not for their one breeding season only. A similar statement holds good with regard to annual and biennial plants. In such cases there might still be a correlation between duration of life and fertility, but it would be of the indirect character, which we actually find in the case of men and women living beyond sixty years of age—a long life means better physique and better physique increased fertility. On the other hand, there is a direct correlation of fertility and duration of life in the case of those animals which generally survive a number of breeding seasons, and it is this correlation which we had at first in view when investigating the influence of duration of life on fertility in man. The discovery of the indirect factor in the correlation referred to above was therefore a point of much interest. For it seems to show that the physique fittest to survive is really the physique which is in itself (and independently of the duration of life) most fecund.
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- Copyright © Institute and Faculty of Actuaries 1900
References
page 458 note * Of course longer life may denote greater chance of male or female meeting female or male, but in this case we have not a graduated fertility, the individual is or is not once fertile.
page 459 note * Roy. Soc. Proc., vol. 65, p. 290.
page 459 note † Second edition, p. 445.
page 459 note ‡ We have also to very heartily thank Mr. L. N. Filon, M.A., and Mr. K. Tressler for aid in the calculations and preparation of diagrams.
page 460 note * Of course a “family” history like that of the Whitney family, professing to deal with all the descendants of a single pair, really contains an immense addition through marriage of other strains.
page 460 note † The existence of a modal value about 45 has already been noted in the resolution of the mortality curve; it is the mode of the middle age mortality component. See Phil. Trans., A, vol. 186, p. 408, and Plate 16.
page 460 note ‡ Phil. Trans., A, vol. 192, p. 257.
page 462 note * See , Yule, Roy. Soc. Proc., vol. 60, p. 477 CrossRefGoogle Scholar.
page 462 note † I have shown in a memoir not yet published (a) how to fit all types of curves, but particular parabolas of any order, by the method of moments; and (b) that such method gives results practically of the same order of exactness as those given by the method of least squares.—K.P.
page 464 note * It has been suggested that this is due to the nature of the record, there being a tendency to enter only the children who survive their parents. Thus the longer the latter live the fewer would be the offspring entered. In other words, we should be under-estimating the correlation between fertility and longevity. But the Quaker birth-records include all children, and their system is uniform. There does not appear any reason on this ground for English and American returns differing so sensibly.
page 466 note * Omitting, for example, the effect of natural selection as evidenced possibly in a greater death-rate in large families, &c.
page 466 note † Phil. Trans., vol. 187, p. 288.
page 467 note * Roy. Soc. Proc., vol. 65, p. 297. The Landed Gentry would appear to be closer than the Peerage to our present material.
page 467 note † It is by no means certain that this is the true view of the case. We have seen that the American women have their maximum mortality in early middle-life, and only a secondary maximum at 70. The maximum mortality of the table prepared by J. P., F.R.S., for the years 1728-57 ( A Collection of the Yearly Bills of Mortality from 1657 to 1758 inclusive, London, 1759 Google Scholar ) occurs about 41 years, and there is no evidence of a maximum at 70 at all. Thus the American data appear to resemble London data of two centuries back.
page 468 note * Roy. Soc. Proc., vol. 65, p. 297.
page 468 note † The average age at death of mothers must in our case closely give the expectation of life of women of 20, for there are few marriages below 20, and we have in our tables included all cases of sterile unions.
page 468 note ‡ Contributions to Vital Statistics, London, 1846 Google ScholarPubMed.
page 469 note * We do not know how J. P.'s table was deduced, but we got the above results by averaging the years lived by those surviving at any age out of the 1,000 born.
page 471 note * The matter is still under investigation, so that this conclusion is stated subject to modification. Of course, the selective death-rate among children may largely remove those not weak from inherited constitution, but by physical or physiological accident. These our method of investigation would throw into the non-selective death-rate.
page 271 note † The Grammar of Science, second edition, pp. 448-9.