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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
selection,
selec- tion,
selection
OMIT banish the belief of the continued creation of new organic beings, or of any great and sudden
modifications
modification
in their structure.
On
On
the
the
Intercrossing
Intercrossing
of
of
Individuals .—
Individuals.
Individuals.
Individuals.
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
case
cases
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
view,
view
was long ago doubtfully suggested by
Andrew
Sprengel,
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
self-fertilises
fertilises
itself for
an eternity
a perpetuity
of generations; but that a cross with another individual is occasionally— perhaps at
very
....
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