338 THE STRUCTURE OF EVOLUTIONARY THEORY
head and limbs tend to vary together in shape and even in color; but several highly
competent judges dispute the correctness of this view" (1868, vol. 2, p. 324). He
also argues that joint slimness in head and limbs of greyhounds, and similar
thickness of both structures in draft horses, might record structural correlation
between putative homologs.
Proceeding further, Darwin considers hair, feathers, hooves, horns and teeth
as "homologous over the whole body" (p. 326). He argues that sheep with a
tendency to grow multiple horns also have "great length and coarseness of fleece."
He also reports that sheep with more curly wool bear more spirally twisted horns,
and that many breeds of hairless dogs grow deficient teeth.
Moving to humans, Darwin tries to relate some forms of inherited baldness to
weakness of dentition, and even claims that rare cases of restored hair in old age
may be accompanied by renewal of teeth. In his most intriguing example, Darwin
discusses Julia Pastrana, the famous "bearded lady" of circus sideshows.
Proclaiming her, with true Victorian sensibility, "a remarkably fine woman" (p.
328), Darwin continues: "... but she had a thick masculine beard and a hairy
forehead; she was photographed, and her stuffed skin was exhibited as a show; but
what concerns us is, that she had in both the upper and lower jaw an irregular
double set of teeth, one row being placed within the other. .. From the redundancy
of the teeth her mouth projected, and her face had a gorilla-like appearance" (p.
328).
Darwin even invokes putative homology—this time between organs of sight
and hearing—to explain the case that he had always found personally most
bothersome: deafness correlated with blue eyes in cats:
The organs of sight and hearing are generally admitted to be homologous,
both with each other and with the various dermal appendages; hence these
parts are liable to be abnormally affected in conjunction ... Here is a more
curious case: white cats if they have blue eyes, are almost always deaf...
This case of correlation in cats has struck many persons as marvelous ...
[But,] we have already seen that the organs of sight and hearing are often
simultaneously affected. In the present instance, the cause probably lies in a
slight arrest of development in the nervous system in connection with the
sense organs. Kittens during the first nine days, whilst their eyes are closed,
appear to be completely deaf; I have made a great clanging noise with a
poker and shovel close to their heads, both when they were asleep and
awake, without producing any effect. ... Now, as long as the eyes continue
closed, the iris is no doubt blue, for in all the kittens which I have seen this
color remains for some time after the eyelids open. Hence if we suppose the
development of the organs of sight and hearing to be arrested at the stage of
the closed eyelids, the eyes would remain permanently blue and the ears
would be incapable of perceiving sound; and we should thus understand
this curious case (pp. 328-329).