domestication, though in different ways. Some of them appear to vary
little, others moderately, others immoderately, to the great
bewilderment of systematic botanists and zoologists, and their
increasing disagreement as to whether various forms shall be held to
be original species or marked varieties. Moreover, the degree to
which the descendants of the same stock, varying in different
directions, may at length diverge is unknown. All we know is, that
varieties are themselves variable, and that very diverse forms have
been educed from one stock.

2. Species of the same genus are not distinguished from each other by
equal amounts of difference. There is diversity in this respect
analogous to that of the varieties of a polymorphous species, some of
them slight, others extreme. And in large genera the unequal
resemblance shows itself in the clustering of the species around
several types or central species, like satellites around their
respective planets. Obviously suggestive this of the hypothesis that
they were satellites, not thrown off by revolution, like the moons of
Jupiter, Saturn, and our own solitary moon, but gradually and
peacefully detached by divergent variation. That such closely related
species may be only varieties of higher grade, earlier origin, or
more favored evolution, is not a very violent supposition. Anyhow, it
was a supposition sure to be made.

3. The actual geographical distribution of species upon the earth's
surface tends to suggest the same notion. For, as a general thing,
all or most of the species of a peculiar genus or other type are
grouped in the same country, or occupy continuous, proximate, or
accessible areas. So well does this rule hold, so general is the
implication that kindred species are or were associated
geographically, that most trustworthy naturalists, quite free from
hypotheses of transmutation, are constantly inferring former
geographical continuity between parts of the world now widely
disjoined, in order to account thereby for the generic similarities
among their inhabitants. Yet no scientific explanation has been
offered to account for the geographical association of kindred
species, except the hypothesis of a common origin.

4. Here the fact of the antiquity of creation, and in particular of
the present kinds of the earth's inhabitants, or of a large part of
them, comes in to rebut the objection, that there has not been time
enough for any marked diversification of