Both these results follow when another division is
made, and when all the least genera, with from only one to four species,
are altogether excluded from the tables. These facts are of plain
signification on the view that species are only strongly marked and
permanent varieties; for wherever many species of the same genus have been
formed, or where, if we may use the expression, the manufactory of species
has been active, we ought generally to find the manufactory still in
action, more especially as we have every reason to believe the process of
manufacturing new species to be a slow one. And this certainly holds true
if varieties be looked at as incipient species; for my tables clearly show,
as a general rule, that, wherever many species of a genus have been formed,
the species of that genus present a number of varieties, that is, of
incipient species, beyond the average. It is not that all large genera are
now varying much, and are thus increasing in the number of their species,
or that no small genera are now varying and increasing; for if this had
been so, it would have been fatal to my theory; inasmuch as geology plainly
tells us that small genera have in the lapse of time often increased
greatly in size; and that large genera have often come to their maxima,
declined, and disappeared. All that we want to show is, that where many
species of a genus have been formed, on an average many are still forming;
and this certainly holds good.
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