[51] In strict accuracy, the law of ancestral inheritance must be described as giving means of determining the probable deviation of any individual from the mean of his own generation, when the deviations of some or all of his ancestry from the types of their respective generations are known. It presupposes (1) no assortative mating, (2) no inbreeding and (3) no selection. Galton's own formula, which supposed that the parents contributed ½, the grandparents ¼, the great-grandparents ⅛, the next generation ⅟16, and so on, is of value now only historically, or to illustrate to a layman the fact that he inherits from his whole ancestry, not from his parents alone.
[52] Johnson, Roswell H., "The Malthusian Principle and Natural Selection," American Naturalist, XLVI (1912), pp. 372-376.
[53] Karl Pearson, The Groundwork of Eugenics, p. 25, London, 1912.
[54] "Let p be the chance of death from a random, not a constitutional source, then 1-p is the chance of a selective death in a parent and 1-p again of a selective death in the case of an offspring, then
(1-p)2 must equal about ⅓, = .36, more exactly ∴ 1-p = .6 and p = .40. In other words, 60% of the deaths are selective."
[55] Archiv f. Rassen-u. Gesellschafts Biologie, VI (1909), pp. 33-43.
[56] Snow, E. C., On the Intensity of Natural Selection in Man, London, 1911.
[57] Biometrika, Vol. X, pp. 488-506, London, May, 1915.
[58] Pearson, Karl, Tuberculosis, Heredity and Environment, London, 1912. Among the most careful contributions to the problem of tuberculosis are those of Charles Goring (On the Inheritance of the Diathesis of Phthisis and Insanity, London, 1910), Ernest G. Pope (A Second Study of the Statistics of Pulmonary Tuberculosis, London, Dulau & Co.), and W. P. Elderton and S. J. Perry (A Third Study of the Statistics of Pulmonary Tuberculosis. The Mortality of the Tuberculous and Sanatorium Treatment), London, 1909. See also our discussion in Chapter I.
[59] While most physicians lay too great stress on the factor of infection, this mistake is by no means universal. Maurice Fishberg, for example (quoted in the Medical Review of Reviews, XXII, 8, August, 1916) states: "For many years the writer was physician to a charitable society, having under his care annually 800 to 1,000 consumptives who lived in poverty and want, in overcrowded tenements, having all opportunities to infect their consorts; in fact most of the consumptives shared their bed with their healthy consorts. Still, very few cases were met with in which tuberculosis was found in both the husband and wife. Widows, whose husbands died from phthisis, were only rarely seen to develop the disease."