[35] _Op. cit._, pp. 170-171.
[36] Thorndike, E. L., "Measurements of Twins," _Arch. of Philos.,
Psych. and Sci. Methods_, No. 1, New York, 1905; summarized in his
_Educational Psychology_, Vol. III, pp. 247-251, New York, 1914.
Measured on a scale where 1 = identity, he found that twins showed a
resemblance to each other of about .75, while ordinary brothers of about
the same age resembled each other to the extent of about .50 only. The
resemblance was approximately the same in both physical and mental
traits.
[37] The quotations in this and the following paragraph are from
_Thorndike's Educational Psychology_, pp. 304-305, Vol. III.
[38] _Biometrika_, Vol. III, p. 156.
[39] "William of Occam's Razor" is the canon of logic which declares
that it is unwise to seek for several causes of an effect, if a single
cause is adequate to account for it.
[40] Schuster, Edgar, _Eugenics_, pp. 150-163, London, 1913.
[41] _Educational Psychology_ (1914), Vol. III, p. 235.
[42] Cobb, Margaret V., _Journal of Educational Psychology_, viii, pp.
1-20, Jan., 1917.
[43] This is not true of the small English school of biometrists,
founded by Sir Francis Galton, W. F. R. Weldon and Karl Pearson, and now
led by the latter.
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