Some of these correlations are very
curious. Mr. Tegetmeier informed Mr. Darwin that the young of white,
yellow, or dun-coloured pigeons are born almost naked, whereas other
coloured pigeons are born well clothed with down. Now, if this
difference occurred between wild species of different colours, it might
be said that the nakedness of the young could not be of any use. But the
colour with which it is correlated might, as has been shown, be useful
in many ways. The skin and its various appendages, as horns, hoofs,
hair, feathers, and teeth, are homologous parts, and are subject to very
strange correlations of growth. In Paraguay, horses with curled hair
occur, and these always have hoofs exactly like those of a mule, while
the hair of the mane and tail is much shorter than usual. Now, if any
one of these characters were useful, the others correlated with it might
be themselves useless, but would still be tolerably constant because
dependent on a useful organ. So the tusks and the bristles of the boar
are correlated and vary in development together, and the former only may
be useful, or both may be useful in unequal degrees.
Pages:
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261