| → continue to exist to 1859 1860 1861 1866 |
| exist at 1869 |
| have survived to 1872 |
|
| → the very process of 1859 1860 1861 1866 |
| their successors, which were gradually rendered more 1869 1872 |
|
| → animal, by some modification of its structure, for 1859 1860 1861 1866 |
| structure of the animal to 1869 1872 |
|
| → But it is 1859 1860 1861 1866 |
| It is, however, 1869 1872 |
|
|
grades of the structure will seldom
→continue to exist to
the present day, for they will have been supplanted by
→the very process of
through natural selection. Furthermore, we may conclude that
between structures fitted for very different habits of life will rarely have been developed at an early period in great numbers and under many subordinate forms. Thus, to return to our imaginary illustration of the
it does not seem probable that fishes capable of true flight would have been developed under many subordinate forms, for taking prey of many kinds in many ways, on the land and in the water, until their organs of flight had come to a high stage of perfection, so as to have given them a decided advantage over other animals in the battle for life. Hence the chance of discovering species with transitional grades of structure in a fossil condition will always be less, from their having existed in lesser numbers, than in the case of species with fully developed structures. |
|
| I will now give two or three instances
diversified and of changed habits in the individuals of the same species.
either case
it would be easy for natural selection to
the
→animal, by some modification of its structure, for
its changed habits, or exclusively
one of its several
habits.
→But it is
difficult to
and immaterial for us, whether habits generally change first and structure afterwards; or whether slight modifications of structure lead to changed habits; both probably often
almost simultaneously. Of cases of changed habits it will suffice merely to allude to that of the many British insects which now feed on exotic plants, or exclusively on artificial substances. Of diversified habits innumerable instances could be given: I have often watched a tyrant flycatcher (Saurophagus sulphuratus) in South America, hovering over one spot
|
