| → with its beak 1872 |
| away 1861 1866 1869 |
|
| → all the slight individual variations in the shape of the beak, which were 1869 1872 |
| each slight variation of beak, 1861 1866 |
|
| → or spontaneous 1869 1872 |
| from the want of other food, or the preservation of chance 1861 1866 |
|
| → to become more 1869 1872 |
| more 1861 1866 |
|
| → or taste; but 1869 1872 |
| but 1861 1866 |
|
| → it was instinct 1869 1872 |
| instinct 1861 1866 |
|
| → varied. 1869 1872 |
| slightly changed; nor can we conjecture by what gradations many instincts have been developed when they relate to organs (such as the mammary glands) on the first origin of which we know nothing. 1861 1866 |
|
| → were independently acquired through 1869 1872 |
| have been acquired by independent acts of 1859 1860 1861 |
| have been independently acquired by 1866 |
|
|
this bird often holds the seeds of the yew between its feet on a branch, and hammers
→with its beak
till it gets
the kernel. Now what special difficulty would there be in natural selection preserving
→all the slight individual variations in the shape of the beak, which were
better and better adapted to break open
until a beak was formed, as well constructed for this purpose as that of the nuthatch, at the same time that
habit, or
→or spontaneous
variations of taste,
the bird
→to become more
and more of a seed-eater? In this case the beak is supposed to be slowly modified by natural selection, subsequently to, but in accordance with, slowly changing
→or taste; but
let the feet of the titmouse vary and grow larger from correlation with the beak, or from any other unknown cause, and
it
improbable that such larger feet
lead the bird to climb more
until it acquired
the remarkable climbing instinct and
of the
In this case a gradual change of structure is supposed to lead to changed instinctive
To take one more case: few instincts are more remarkable than that which leads the swift of the Eastern Islands to make its nest wholly of inspissated saliva. Some birds build their nests of mud, believed to be moistened with saliva; and one of the swifts of North America makes its nest (as I have seen) of sticks agglutinated with saliva, and even with flakes of this substance. Is it then very improbable that the natural selection of individual swifts, which secreted more and more saliva, should at last produce a species with instincts leading it to neglect other materials, and to make its nest exclusively of inspissated saliva? And so in other cases. It
admitted that in many instances we cannot conjecture whether
→it was instinct
or structure
first
→varied.
|
|
| No doubt many instincts of very difficult explanation could be opposed to the theory of natural
cases, in which we cannot see how an instinct could
have originated; cases, in which no intermediate gradations are known to exist; cases of instinct of
such trifling importance, that they could hardly have been acted on by natural selection; cases of instincts almost identically the same in animals so remote in the scale of nature, that we cannot account for their similarity by inheritance from a common
and
believe that they
→were independently acquired through
natural selection. I will not here enter on these several cases, but will confine myself to one special difficulty, which at first appeared to me insuperable, and actually fatal to
whole theory. I allude to the neuters or sterile females in insect-communities: for these neuters often differ widely in instinct and in structure
|
