All Mr. Mivart's objections will be, or have been, considered in the
present volume. The one new point which appears to have struck many
readers is, "That natural selection is incompetent to account for the
incipient stages of useful structures." This subject is intimately
connected with that of the gradation of the characters, often accompanied
by a change of function, for instance, the conversion of a swim-bladder
into lungs, points which were discussed in the last chapter under two
headings. Nevertheless, I will here consider in some detail several of the
cases advanced by Mr. Mivart, selecting those which are the most
illustrative, as want of space prevents me from considering all.
The giraffe, by its lofty stature, much elongated neck, fore legs, head and
tongue, has its whole frame beautifully adapted for browsing on the higher
branches of trees. It can thus obtain food beyond the reach of the other
Ungulata or hoofed animals inhabiting the same country; and this must be a
great advantage to it during dearths. The Niata cattle in South America
show us how small a difference in structure may make, during such periods,
a great difference in preserving an animal's life. These cattle can browse
as well as others on grass, but from the projection of the lower jaw they
cannot, during the often recurrent droughts, browse on the twigs of trees,
reeds, etc., to which food the common cattle and horses are then driven; so
that at these times the Niatas perish, if not fed by their owners.
Pages:
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346