The former are also grouped in little clusters, like
varieties round species; and they present other analogies with varieties,
as was shown in our second chapter. On this same principle we can
understand how it is that specific characters are more variable than
generic characters; and how the parts which are developed in an
extraordinary degree or manner are more variable than other parts of the
same species. Many analogous facts, all pointing in the same direction,
could be added.
Although very many species have almost certainly been produced by steps not
greater than those separating fine varieties; yet it may be maintained that
some have been developed in a different and abrupt manner. Such an
admission, however, ought not to be made without strong evidence being
assigned. The vague and in some respects false analogies, as they have
been shown to be by Mr. Chauncey Wright, which have been advanced in favour
of this view, such as the sudden crystallisation of inorganic substances,
or the falling of a facetted spheroid from one facet to another, hardly
deserve consideration. One class of facts, however, namely, the sudden
appearance of new and distinct forms of life in our geological formations
supports at first sight the belief in abrupt development. But the value of
this evidence depends entirely on the perfection of the geological record,
in relation to periods remote in the history of the world.
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