| → may under new conditions of life 1859 1860 1861 1866 1869 |
| under new conditions of life may 1872 |
|
| → have 1859 1860 1861 1866 1869 |
| it may have 1872 |
|
|
not linked together by a multitude of intermediate
partly because the process of natural selection
always
very slow, and
at any one
on a
few forms; and partly because the very process of natural selection
implies the continual supplanting and extinction of
and intermediate
Closely allied species, now living on a continuous area, must often have been formed when the area was not continuous, and when the conditions of life did not insensibly graduate away from one part to another. When two varieties are formed in two districts of a continuous area, an intermediate variety will often be formed, fitted for an intermediate zone; but from reasons assigned, the intermediate variety will usually exist in lesser numbers than the two forms which it connects; consequently the two latter, during the course of further modification, from existing in greater numbers, will have a great advantage over the less numerous intermediate variety, and will thus generally succeed in supplanting and
it. |
|
| We have seen in this chapter how cautious we should be in concluding that the most different habits of life could not graduate into each other; that a bat, for instance, could not have been formed by natural selection from an animal which at first
only
through the air. |
|
| We have seen that a species
→may under new conditions of life
change its
or
→have
diversified habits, with some
very unlike those of its nearest congeners. Hence we can understand, bearing in mind that each organic being is trying to live wherever it can live, how it has arisen that there are upland geese with webbed feet, ground woodpeckers, diving thrushes, and petrels with the habits of auks. |
|
| Although the belief that an organ so perfect as the
|
