| → were formed 1859 1860 1861 1866 |
| have been developed 1869 1872 |
|
| → simple. 1859 1860 1861 1866 1869 |
| comparatively simple; and we can understand to a large extent the laws governing their imperfect development. 1872 |
|
| → breeds,— 1859 1860 1861 1866 |
| breeds of sheep,— 1869 |
| breeds of sheep, 1872 |
|
| → monsters. 1859 1860 1861 1866 1869 |
| monsters; but I doubt whether any of these cases throw light on the origin of rudimentary organs in a state of nature, further than by showing that rudiments can be produced; for the balance of evidence clearly indicates that species under nature do not undergo great and abrupt changes. 1872 |
|
| → I doubt whether any of these cases throw light on the origin of rudimentary organs in a state of nature, further than by showing that rudiments can be produced; for I doubt whether species under nature ever undergo abrupt changes. 1859 1860 1861 1866 1869 |
| we learn from the study of our domestic productions that the disuse of parts leads to their reduced size; and that the result is inherited. 1872 |
|
| → to 1859 1860 1861 1866 |
| by beasts of prey to 1869 |
|
| ↑ 3 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| It appears probable that disuse has been the main agent in rendering organs rudimentary.
It would at first lead by slow steps to the more and more complete reduction of a part, until at last it became rudimentary,— as in the case of the eyes of animals inhabiting dark caverns, and of the wings of birds inhabiting oceanic islands, which have seldom been forced by beasts of prey to take flight, and have ultimately lost the power of flying.
Again, an organ, useful under certain conditions, might become injurious under others, as with the wings of beetles living on small and exposed islands; and in this case natural selection will have aided in reducing the organ, until it was rendered harmless and rudimentary.
|
|
| → function, 1859 1860 1861 1866 |
| structure and function, 1869 1872 |
|
|
in order to excrete horny matter, as that the rudimentary nails on the fin of the manatee
→were formed
for this
|
|
| On
view of descent with modification, the origin of rudimentary organs is
→simple. We have plenty of cases of rudimentary organs in our domestic productions,— as the stump of a tail in tailless breeds,— the vestige of an ear in earless
→breeds,—
the reappearance of minute dangling horns in hornless breeds of cattle, more especially, according to Youatt, in young animals,— and the state of the whole flower in the cauliflower. We often see rudiments of various parts in
→monsters. But
→I doubt whether any of these cases throw light on the origin of rudimentary organs in a state of nature, further than by showing that rudiments can be produced; for I doubt whether species under nature ever undergo abrupt changes. I believe that disuse has been the main agency; that it has led in successive generations to the gradual reduction of various organs, until they have become rudimentary,— as in the case of the eyes of animals inhabiting dark caverns, and of the wings of birds inhabiting oceanic islands, which have seldom been forced
→to
take flight, and have ultimately lost the power of flying. Again, an organ useful under certain conditions, might become injurious under others, as with the wings of beetles living on small and exposed islands; and in this case natural selection would continue slowly to reduce the organ, until it was rendered harmless and rudimentary. ↑ |
|
| Any change in
→function,
which can be effected by
small
is within the power of natural selection; so that an organ rendered,
changed habits of life, useless or injurious for one purpose, might
be modified and used for another purpose.
organ
retained for one alone of its former functions.
|
