In the same way that a knife which has to cut all sorts of things
may be of almost any shape; whilst a tool for some particular purpose must
be of some particular shape. Natural selection, it should never be
forgotten, can act solely through and for the advantage of each being.
Rudimentary parts, as is generally admitted, are apt to be highly variable.
We shall have to recur to this subject; and I will here only add that their
variability seems to result from their uselessness, and consequently from
natural selection having had no power to check deviations in their
structure.
A PART DEVELOPED IN ANY SPECIES IN AN EXTRAORDINARY DEGREE OR MANNER, IN
COMPARISON WITH THE SAME PART IN ALLIED SPECIES, TENDS TO BE HIGHLY
VARIABLE.
Several years ago I was much struck by a remark to the above effect made by
Mr. Waterhouse. Professor Owen, also, seems to have come to a nearly
similar conclusion. It is hopeless to attempt to convince any one of the
truth of the above proposition without giving the long array of facts which
I have collected, and which cannot possibly be here introduced. I can only
state my conviction that it is a rule of high generality. I am aware of
several causes of error, but I hope that I have made due allowances for
them. It should be understood that the rule by no means applies to any
part, however unusually developed, unless it be unusually developed in one
species or in a few species in comparison with the same part in many
closely allied species.
Pages:
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246