That varieties of this doubtful nature are far from uncommon cannot be disputed. Compare the several floras of Great Britain, of
France France 1859 1860 | France, 1861 1866 1869 1872 |
or of the United States, drawn up by different botanists, and see what a surprising number of forms have been ranked by one botanist as good species, and by another as mere varieties. Mr. H. C. Watson, to whom I lie under deep obligation for assistance of all kinds, has marked for me 182 British plants, which are generally considered as varieties, but which have all been ranked by botanists as species; and in making this list he has omitted many trifling varieties, but which nevertheless have been ranked by some botanists as species, and he has entirely omitted several highly polymorphic genera. Under genera, including the most polymorphic forms, Mr. Babington gives 251 species, whereas Mr. Bentham gives only
112,— 112,— 1859 1860 1861 1872 | 112,—a 1866 1869 |
a a 1859 1860 1861 1872 | a 1866 1869 |
difference of 139 doubtful forms! Amongst animals which unite for each birth, and which are highly locomotive, doubtful forms, ranked by one zoologist as a species and by another as a variety, can rarely be found within the same country, but are common in separated areas. How many of
those those 1859 1860 1861 1866 1869 | the 1872 |
birds and insects in North America and Europe, which differ very slightly from each other, have been ranked by one eminent naturalist as undoubted species, and by another as varieties, or, as they are often called,
as as 1859 1860 1861 1866 1869 | as 1872 |
geographical races! ↑6 blocks not present in 1859 1860 1861; present in 1866 1869 1872 | Mr. Wallace, in several valuable papers lately published
on the various animals, especially on the Lepidoptera, inhabiting the islands of the great Malayan archipelago, shows that they may be classed under variable and under
local forms, under
geographical races or sub-species, and as true representative species.
The variable
forms vary much within the limits of the same island.
The local forms of the same species
are moderately constant and distinct in each separate island; but when all such
forms
from
the several islands are compared,
the differences become
so slight,
numerous,
and graduated, that it is impossible to define or describe many of
them, though at the same time the extreme forms are sufficiently distinct.
The geographical races or sub-species are local forms completely fixed and isolated; but as they do not differ from each other by strongly marked and important characters, "there is no possible test but individual opinion to determine which of them shall be considered as species and which as varieties."
Lastly, representative species fill the same place in the natural economy of each island as do the local forms and sub-species; but as they are distinguished from each other by a greater,
though not by a definite,
amount of difference than that between the local forms and sub-species, they are almost universally ranked by naturalists as true species.
Nevertheless, no certain criterion can possibly be given by which variable forms, local forms, sub-species, and representative species can be recognised.
|
Many Many 1859 1860 1861 |
Many
1866 1869 1872 |
years ago, when comparing, and seeing others compare, the birds from the
separate separate 1859 1860 1861 | closely neighbouring 1866 1869 1872 |
islands of the Galapagos
Archipelago, Archipelago, 1859 1860 1861 1866 | archipelago, 1869 1872 |
both both 1859 1860 1861 1866 1869 | both 1872 |
one with another, and with those from the American mainland, I was much struck how entirely vague and arbitrary is the distinction between species and varieties. On the islets of the little Madeira group there are many insects which are characterized as varieties in Mr. Wollaston's admirable work, but which
it cannot be doubted would it cannot be doubted would 1859 1860 |
certainly would 1861 1866 |
would certainly 1869 1872 |
|