| → exist at 1869 |
| continue to exist to 1859 1860 1861 1866 |
| have survived to 1872 |
|
| → their successors, which were gradually rendered more 1869 1872 |
| the very process of 1859 1860 1861 1866 |
|
|
live on the
and seeing that we have flying birds and mammals, flying insects of the most diversified types, and formerly had flying reptiles, it is conceivable that flying-fish, which now glide far through the air, slightly rising and turning by the aid of their fluttering fins, might have been modified into perfectly winged animals. If this had been effected, who would have ever imagined that in an early transitional state they had been
of the open ocean, and had used their incipient organs of flight exclusively, as far as we know, to escape being devoured by other fish? |
|
| When we see any structure highly perfected for any particular habit, as the wings of a bird for flight, we should bear in mind that animals displaying early
grades of the structure will seldom
→exist at
the present day, for they will have been supplanted by
→their successors, which were gradually rendered more
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
|
