| → OMIT 1872 |
| if it be a true principle, 1859 1860 1861 1866 1869 |
|
| → (with the exception of the curious and not well-understood 1860 1861 1866 1869 1872 |
| unite for each birth; but in the 1859 |
|
| → parthenogenesis) unite for each birth; but in the case of hermaphrodites 1860 1861 1866 1869 1872 |
| hermaphrodites 1859 |
|
| → there is reason 1869 1872 |
| I am strongly inclined 1859 1860 1861 1866 |
|
| → was long ago doubtfully 1872 |
| I may add, was first 1859 |
| was first 1860 1861 1866 1869 |
|
| → Knight, and Kölreuter. 1872 |
| Knight. 1859 1860 1861 1866 1869 |
|
| → and made so many experiments, showing, 1872 |
| showing, 1859 1860 1861 1866 1869 |
|
| → OMIT 1869 1872 |
| (utterly ignorant though we be of the meaning of the law) 1859 1860 1861 1866 |
|
| → intervals of time— 1869 1872 |
| intervals— 1859 1860 1861 1866 |
|
|
banished such views as the excavation of a great valley by a single diluvial wave, so will natural
→OMIT
banish the belief of the continued creation of new organic beings, or of any great and sudden
in their structure. |
|
|
| I must here introduce a short digression. In the case of animals and plants with separated sexes, it is of course obvious that two individuals must always
→(with the exception of the curious and not well-understood
of
→parthenogenesis) unite for each birth; but in the case of hermaphrodites
this is far from obvious. Nevertheless
→there is reason
to believe that with all hermaphrodites two individuals, either occasionally or habitually, concur for the reproduction of their kind. This
→was long ago doubtfully
suggested by
→Knight, and Kölreuter. We shall presently see its importance; but I must here treat the subject with extreme brevity, though I have the materials prepared for an ample discussion. All vertebrate animals, all insects, and some other large groups of animals, pair for each birth. Modern research has much diminished the number of supposed hermaphrodites, and of real hermaphrodites a large number pair; that is, two individuals regularly unite for reproduction, which is all that concerns us. But still there are many hermaphrodite animals which certainly do not habitually pair, and a vast majority of plants are hermaphrodites. What reason, it may be asked, is there for supposing in these cases that two individuals ever concur in reproduction? As it is impossible here to enter on details, I must trust to some general considerations alone. |
|
| In the first place, I have collected so large a body of facts,
→and made so many experiments, showing,
in accordance with the almost universal belief of breeders, that with animals and plants a cross between different varieties, or between individuals of the same variety but of another strain, gives vigour and fertility to the offspring; and on the other hand, that
close
interbreeding diminishes vigour and fertility; that these facts alone incline me to believe that it is a general law of nature
→OMIT
that no organic being
itself for
of generations; but that a cross with another individual is occasionally— perhaps at
long
→intervals of time—
indispensable. |
|
| On the belief that this is a law of nature, we can, I think, understand several large classes of facts, such as the following, which on any other view are inexplicable. Every hybridizer knows how unfavourable exposure to wet is to the fertilisation of a flower, yet
|
