[18] Dr. Reid is the author who has most effectively called attention to this relation between alcohol and natural selection. Those interested will find a full treatment in his books, _The Present Evolution of Man_, _The Laws of Heredity_, and _The Principles of Heredity_. [19] _Principles of Psychology_, ii, p. 543. [20] Leon J. Cole points out that this may be due in considerable part to less voluntary restriction of offspring on the part of those who are often under the influence of alcohol. [21] For a review of the statistical problems involved, see Karl Pearson. An attempt to correct some of the misstatements made by Sir Victor Horsley, F. R. S., F. R. C. S., and Mary D. Sturge, M. D., in their criticisms of the Galton Laboratory Memoir: _First Study of the Influence of Parental Alcoholism_, etc.; and Professor Pearson's various popular lectures, also _A Second Study of the Influence of Parental Alcoholism on the Physique and Intelligence of Offspring_. By Karl Pearson and Ethel M. Elderton. Eugenics Laboratory Memoir Series XIII. [22] _A First Study of the Influence of Parental Alcoholism on the Physique and Intelligence of Offspring._ By Ethel M. Elderton and Karl Pearson. Eugenics Laboratory Memoir Series X. Harald Westergaard, who reexamined the Elderton-Pearson data, concludes that considerable importance is to be attached to the selective action of alcohol, the weaklings in the alcoholic families having been weeded out early in life. [23] Prohibition would have some _indirect_ eugenic effects, which will be discussed in Chapter XVIII. [24] Chapter XXX, verses 31-43. A knowledge of the pedigree of Laban's cattle would undoubtedly explain where the stripes came from. It is interesting to note how this idea persists: a correspondent has recently sent an account of seven striped lambs born after their mothers had seen a striped skunk. The actual explanation is doubtless that suggested by Heller in the _Journal of Heredity_, VI, 480 (October, 1915), that a stripe is part of the ancestral coat pattern of the sheep, and appears from time to time because of reversion. [25] Such a skin affection, known as icthyosis, xerosis or xeroderma, is usually due to heredity. Davenport says it "is especially apt to be found in families in which consanguineous marriages occur and this fact, together with the pedigrees [which he studied], suggests that it is due to the absence of some factor that controls the process of cornification of the skin. On this hypothesis a normal person who belongs to an affected family may marry into a normal family with impunity, but cousin marriages are to be avoided." See Davenport, C. B., _Heredity in Relation to Eugenics_, p. 134. New York, 1911.