14 
Pigmentation, Susceptibility and Race Selection 
the fatal distemper. In Virginia white pigs perish from eating certain roots 
which dark pigs can eat without injury. White chickens are more subject than 
dark coloured chickens to certain parasitic worms. In cattle susceptibility to the 
attack of flies is correlated with colour, as also is the liability to be poisoned by 
certain plants, the white varieties suffering most severely *. Certain forms of 
blindness are said to be associated with the colour of the hair. Thus Darwin cites 
the case of a man with black hair and a woman with light coloured hair, both of 
sound constitution, who married, and had nine children, all of whom were born blind : 
of these children, five with dark hair and brown iris were afflicted with amaurosis : 
the four others, with light coloured hair and blue iris, had amaurosis and cataract 
combined f. 
Then again the tubercular child is loosely recognized by certain features, 
including the quality of the skin, the brightness of the eyes and the length and 
pigmentation of the eyelashes. 
Beddoe states that phthisis and cancer are more prevalent among dark-haired 
persons \, Tocher has shown§ that on an average more persons become insane in 
parts of Scotland where there is an excess of light-eyed persons in the population, 
and in a much less degree where there is an excess of dark-haired persons. Lunacy, 
he states, is distinctly correlated positively to light eyes and in a much less degree 
to dark hair, and is distinctly correlated negatively to red hair, and in a less 
degree to dark eyes. There is thus a greater tendency to insanity among light- 
eyed and dark-haired persons, and a lesser tendency to insanity among red-haired 
and dark-eyed persons, compared in both cases with the general population. He 
goes on to say that these are only statistical facts, and offers no explanation as 
to how or why presence or absence of pigment comes to be associated with insanity. 
When he extended his inquiry || to discover whether the excess of any particular 
hair or eye colour is associated with physical or mental defects such as blindness, 
deafness and imbecility, he found that the distribution of cases of mental affection 
differs from that of the last three classes, namely, that excesses in the number of 
cases of imbecility, blindness and deafness, occur in the region of excesses of blue 
eyes and of dark and jet black hair. 
It is well known that in the lower animals pigmentation has an important 
function. It seems, especially in the organs of sense, to be essential to their full 
development. Albinos in all species are apt to be defective in keenness of sense. 
Darwin gives numerous examples of the defective senses of such non-pigmented 
animals. White cats with blue eyes, he states, are almost always deaf. He cites 
a remarkable case, in which the iris at the end of four months began to grow dark 
coloured, and then for the first time the cat began to hear 11. Histological exami- 
* Darwin : Origin of Species, p. 236. 
t Darwin: Variation of Animals under Domestication, Vol. n. p. 328. 
+ Beddoe : Races of Britain, p. 224. 
§ Tocher: "Anthropometry of Scottish Insane." Biometrika, Vol. v. p. 344. 
|| Tocher: "Pigmentation Survey of School Children in Scotland." Biometrika, Vol. VI. p. 198. 
If Darwin : Variation of Animals under Domestication, Vol. n. p. 329. 
