[1] See Woods, Frederick Adams, "Laws of Diminishing Environmental Influences," Popular Science Monthly, April, 1910, pp. 313-336; Huxley, J. S., The Individual in the Animal Kingdom, Cambridge and New York, 1912. Pike, F. H., and Scott, E. L., "The Significance of Certain Internal Conditions of the Organism in Organic Evolution," American Naturalist, Vol. XLIX, pp. 321-359, June, 1915.
[2] There is one line of experiment which is simple and striking enough to deserve mention—namely, ovarian transplantation. A description of this is given in Appendix A.
[3] Galton, Francis, Inquiries into Human Faculty, 1907 edition, pp. 153-173. This volume of Galton's, which was first published in 1883, has been reissued in Everyman's Library, and should be read by all eugenists.
[4] What is said here refers to positive correlations, which are the only kind involved in this problem. Correlations may also be negative, lying between 0 and -1; for instance, if we measured the correlation between a man's lack of appetite and the time that had elapsed since his last meal, we would have to express it by a negative fraction, the minus sign showing that the greater his satiety, the less would be the time since his repast. The best introduction to correlations is Elderton's Primer of Statistics (London, 1912).
[5] Dr. Thorndike's careful measurements showed that it is impossible to draw a hard and fast line between identical twins and ordinary twins. There is no question as to the existence of the two kinds, but the ordinary twins may happen to be so nearly alike as to resemble identical twins. Accordingly, mere appearance is not a safe criterion of the identity of twins. His researches were published in the Archives of Philosophy, Psychology and Scientific Methods, No. 1, New York, 1905.
[6] A First Study of the Inheritance of Vision and the Relative Influence of Heredity and Environment on Sight. By Amy Barrington and Karl Pearson. Eugenics Laboratory (London), Memoir Series V.
[7] Dr. James Alexander Wilson, assistant surgeon of the Opthalmic Institute, Glasgow, published an analysis of 1,500 cases of myopia in the British Medical Journal, p. 395, August 29, 1914. His methods are not above criticism, and too much importance should not be attached to his results, which show that in 58% of the cases heredity can be credited with the myopia of the patient. In 12% of the cases it was due to inflammation of the cornea (keratitis) while in the remaining 30% no hereditary influence could be proved, but various reasons made him feel certain that in many cases it existed. The distribution of myopia by trades and professions among his patients is suggestive: 65% of the cases among school children showed myopic heredity; 63% among housewives and domestic servants; 68% among shop and factory works; 60% among clerks and typists; 60% among laborers and miners. If environment really played an active part, one would not expect to find this similarity in percentages between laborers and clerks, between housewives and schoolteachers, etc.
[8] The Influence of Unfavourable Home Environment and Defective Physique on the Intelligence of School Children. By David Heron. Eugenics Laboratory (London), Memoir Series No. VIII.
[9] Hereditary Genius; an Inquiry into its Laws and Consequences. London, 1869.
[10] Woods, Frederick Adams, "Heredity and the Hall of Fame," Popular Science Monthly, May, 1913.