Moreover, the species of the large
genera which present any varieties, invariably present a larger
average number of varieties than do the species of the small genera.
Both these results follow when another division is made, and when all
the smallest genera, with from only one to four species, are
absolutely 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 is the case, 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.
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