With species in a state of nature, every naturalist has in fact brought descent into his classification; for he includes in his lowest grade, or
that of
the the 1869 | a 1859 1860 1861 1866 | the 1872 |
species, the two sexes; and how enormously these sometimes differ in the most important characters, is known to every naturalist: scarcely a single fact can be predicated in common of the males
and hermaphrodites of certain cirripedes, when adult,
and yet no one dreams of separating them. As soon as the three Orchidean forms, Monachanthus,
Myanthus, and Catasetum, which had previously been ranked as three distinct genera, were known to be sometimes produced on the same plant, they were immediately considered as varieties; and
now I have been able to show that they are
the male, female, and hermaphrodite forms of the same species. The naturalist includes as one species the several
larval stages of the same individual, however much they may differ from each other and from the adult;
as he likewise includes
the so-called alternate generations of Steenstrup, which can only in a technical sense be considered as the same individual. He includes monsters;
he includes
varieties, not solely because they closely resemble
the parent-form, but because they are descended from it. ↑2 blocks not present in 1866 1869 1872; present in 1859 1860 1861 | He who believes that the cowslip is descended from the primrose, or conversely, ranks them together as a single species, and gives a single definition.
As soon as three Orchidean forms (Monochanthus, Myanthus, and Catasetum), which had previously
been ranked as three distinct genera, were known to be sometimes produced on the same spike, they were immediately included as a single species.
|
↑5 blocks not present in 1860 1861 1866 1869 1872; present in 1859 | But it may be asked, what ought we to do, if it could be proved that one species of kangaroo had been produced, by a long course of modification, from a bear?
Ought we to rank this one species with bears, and what should we do with the other species?
The supposition is of course preposterous; and I might answer by the
argumentum
ad
hominem
,
and ask what should be done if a perfect kangaroo were seen to come out of the womb of a bear?
According to all analogy, it would be ranked with bears; but then assuredly all the other species of the kangaroo family would have to be classed under the bear genus.
The whole case is preposterous; for where there has been close descent in common, there will certainly be close resemblance or affinity.
|
|
As descent has universally been used in classing together the individuals of the same species, though the males and females and larvæ are sometimes extremely different; and as it has been used in classing varieties which have undergone a certain, and sometimes a considerable amount of modification, may not this same element of descent have been unconsciously used in grouping species under genera, and genera under higher groups, though in these cases the modification has been greater in degree, and has taken a longer time to complete?
I believe it has thus
been unconsciously used; and only thus
can I understand the several rules and guides which have been followed by our best systematists.
We We 1859 1860 1861 1866 1869 | As we 1872 |
have no written
pedigrees; pedigrees; 1859 1860 1861 1866 1869 | pedigrees, 1872 |
we
have to make out have to make out 1859 1860 1861 1866 1869 |
are forced to trace 1872 |
community of descent by resemblances of any kind. Therefore we choose those characters
which, which, 1859 1860 1861 1866 1869 | which 1872 |
as far as we can judge, as far as we can judge, 1859 1860 1861 1866 1869 |
OMIT 1872 |
are the least likely to have been
modified modified 1859 1860 1861 1866 1869 | modified, 1872 |
in relation to the conditions of life to which each species has been recently exposed. Rudimentary structures on this view are as good as, or even sometimes better than, other parts of the organisation. We care not how trifling a character may be— let it be the mere inflection of the angle of the jaw, the manner in which an
insects insects 1869 | insect's 1859 1860 1861 1866 1872 |
wing is folded, whether the skin be covered by hair or feathers— if it prevail throughout many and different species, especially those having very different habits of life, it assumes high value; for we can account
|