| → extends to 1859 1860 1861 1866 |
| apparently extends to 1869 |
| holds good with 1872 |
|
| → that 1859 1860 1861 1866 1869 |
| which I have elsewhere given, that 1872 |
|
| → we plainly see that 1859 1860 1861 1866 |
| OMIT 1869 1872 |
|
| → that is between members of different strains or sub-breeds, 1859 1860 1861 1866 |
| which differ to a certain extent, 1869 1872 |
|
| → offspring. 1859 1860 1861 1866 |
| offspring; and that close interbreeding continued during several generations between the nearest relations, especially if these be kept under the same conditions of life, almost always induces weakness and sterility. 1869 |
| offspring; 1872 |
|
| → I believe, indeed, from the facts alluded to in our fourth chapter, that a certain amount of crossing is indispensable even with hermaphrodites; 1859 1860 1861 1866 |
| OMIT 1872 |
|
| → always induces weakness and sterility in the progeny. 1859 1860 1861 1866 |
| almost always leads to decreased size, weakness, or sterility. 1872 |
|
| → varied and become 1859 1860 1861 1866 1869 |
| been subjected to 1872 |
|
| → give 1859 1860 1861 1866 1869 |
| conditions, or which have slightly varied, give 1872 |
|
| → that greater changes, or changes of a particular nature, often render 1859 1860 1861 1866 1869 |
| OMIT 1872 |
|
| → in some degree 1859 1860 1861 1866 1869 |
| long habituated to certain uniform conditions under a state of nature, when subjected, as under confinement, to a considerable change in their conditions, very frequently are rendered more or less 1872 |
|
| → that greater crosses, that is 1859 1860 1861 1866 1869 |
| we know that a 1872 |
|
| → males and females which 1859 1860 1861 1866 1869 |
| two forms, that 1872 |
|
| → cannot persuade myself 1859 1860 1861 1866 1869 |
| am fully persuaded 1872 |
|
| → parallelism is 1859 1860 1861 1866 1869 |
| double parallelism is by no means 1872 |
|
| ↑ 3 blocks not present in 1859 1860 1861 1866 1869; present in 1872 |
| He who is able to explain why the elephant and a multitude of other animals are incapable of breeding when kept under only partial confinement in their native country, will be able to explain the primary cause of hybrids being so generally sterile.
He will at the same time be able to explain how it is that the races of some of our domesticated animals, which have often been subjected to new and not uniform conditions, are quite fertile together, although they are descended from distinct species, which would probably have been sterile if aboriginally crossed.
The above two parallel series of facts seem to be connected together by some common but unknown bond, which is essentially related to the principle of life; this principle, according to Mr. Herbert Spencer, being that life depends on, or consists in, the incessant action and reaction of various forces, which, as throughout nature, are always tending towards an equilibrium; and when this tendency is slightly disturbed by any change, the vital forces gain in power.
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