1) no assortative mating, (2) no
inbreeding and (3) no selection. Galton's own formula, which supposed
that the parents contributed 1/2, the grandparents 1/4, the
great-grandparents 1/8, the next generation 1/16, 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 1/3, = .36, more exactly 'therefore' 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."

[60] In 9th Trans. of _American Assoc