| → rather strongly marked variations, 1872 |
| variations, 1869 |
|
| → to them, as 1872 |
| as 1869 |
|
| ↑ 1 blocks not present in 1859 1860 1861 1866 1872; present in 1869 |
| The conditions might indeed act in so energetic and definite a manner as to lead to the same modification in all the individuals of the species without the aid of selection.
|
|
| → Or 1872 |
| But we may suppose that the conditions sufficed to affect 1869 |
|
| → may have been thus affected, of which fact several instances 1872 |
| and several such cases 1869 |
|
| → Thus Graba estimates that about one-fifth of the guillemots 1872 |
| for instance, it has been estimated by Graba that 1869 |
|
| → OMIT 1872 |
| about one-fifth of the guillemots, which all breed together, 1869 |
|
| → so well marked, that it 1872 |
| and this 1869 |
|
| → In cases of this kind, 1872 |
| Now, in such cases, 1869 |
|
| → To 1872 |
| With reference to 1869 |
|
| → in eliminating variations of all kinds, I shall have to recur; but it may be here remarked 1872 |
| and of competition, it should be borne in mind 1869 |
|
|
would have only a slightly better chance of surviving and breeding; and this chance would go on decreasing in the succeeding generations. The justice of these remarks cannot, I think, be disputed. If, for instance, a bird of some kind could procure its food more easily by having its beak curved, and if one were born with its beak strongly curved, and which consequently flourished, nevertheless there would be a very poor chance of this one individual perpetuating its kind to the exclusion of the common form; but there can hardly be a doubt, judging by what we see taking place under domestication, that this result would follow from the preservation during many generations of a large number of individuals with more or less
beaks, and from the destruction of a still larger number with the straightest beaks. |
|
| It should not, however, be overlooked that certain
→rather strongly marked variations,
which no one would rank as mere individual differences, frequently recur owing to a similar organisation being similarly acted on,—of which fact numerous instances could be given with our domestic productions. In such cases, if
varying individual did not actually transmit to its offspring its newly-acquired character, it would undoubtedly
→to them, as
long as the existing conditions remained the same, a still stronger tendency to vary in the same manner. ↑
There can also be little doubt that the tendency to vary in the same manner has often been so strong that all the individuals of the same species have been similarly modified without the aid of any form of selection.
→Or
only a third,
or tenth part of the
→may have been thus affected, of which fact several instances
could be
→Thus Graba estimates that about one-fifth of the guillemots
in the Faroe Islands
→OMIT
consist of a
→so well marked, that it
was formerly ranked as a distinct species under the name of Uria lacrymans.
→In cases of this kind,
if the variation were of a beneficial nature, the original form would soon be supplanted by the modified form, through the survival of the fittest. |
|
|
→To
the effects of intercrossing
→in eliminating variations of all kinds, I shall have to recur; but it may be here remarked
that most animals and plants keep to their proper homes, and do not needlessly wander about; we see this even with migratory birds, which almost always return to the same
Consequently each newly-formed variety would generally be at first local, as seems to be the common rule with varieties in a state of nature; so that similarly modified individuals would soon exist in a small body together, and would often breed together. If the new variety
successful in its battle for life, it would slowly spread from a central
|
