The only series of data for hair color in husband and wife (where one may not suspect artificial selection of cases) is that given by Mr. Galton for the parents of English scientific men. I have grouped his data into three classes, and calculated the coefficient of mean square contingency, which is + .34. No stress is to be laid on the result, since the number of cases is small and the coarse grouping—which is necessary if the constant is to be calculated at all—unsatisfactory.
4. Physical Defects and Pathological Conditions
To Alexander Graham Bell probably belongs the credit of first laying great stress upon the social consequences of assortative mating. The title of his memoir, "Upon the Formation of a Deaf Variety of the Human Race," sufficiently indicates the seriousness with which he regarded the intermarriage of the deaf.
Probably assortative mating for deafness is more nearly perfect than that for any other known character. The reasons for this are patent. Hearing individuals rarely choose non-hearing mates. When both partners are deaf, on the other hand, they are united by the strong bond of fellowship and sympathy growing out of their similar condition, they communicate with each other with perfect ease and freedom, and the social interests and sympathies outside their own home are the same.
The extensive records given by Fay rather than those used by Bell in his pioneer study may furnish illustrations.
Table III. shows that in the marriages of the deaf, 72.5 per cent.
|Marriages of the Deaf||Number||Percentage|
|Both partners deaf||3,242||72.512|
|One partner deaf; the other hearing||894||19.995|
|One partner deaf; the other unreported whether deaf or hearing.||335||7.493|
have both of the contracting parties deaf as contrasted with 20 per cent. in which one is deaf and the other a hearing person. When we consider that in the general population of the United States there are roundly 1,500 hearing persons to one deaf, and consequently about 1,500 hearing persons to one deaf from whom a given deaf individual might seek to select a life partner, we see to what enormous extent sexual selection is at work for this character.
- Galton, F., "English Men of Science," p. 21, 1895.
- Bell, A. G., Mem. Nat. Acad. Sci., Vol. 2, pp. 179-262, 1883.
- Fay, E. A., "Marriages of the Deaf in America," Washington (Volta Bureau), 1898.
- Schuster (Biometrika, Vol. 4, p. 473, 1906) was unable to calculate the precise intensity of the assortative mating coefficients for deafness because of the mathematical difficulties involved, but it is certainly considerably higher than + .90.