n modifying
and adapting the various forms of life to their several conditions
and stations, must be judged of by the general tenour and balance of
evidence given in the following chapters. But we already see how it
entails extinction; and how largely extinction has acted in the world's
history, geology plainly declares. Natural selection, also, leads to
divergence of character; for more living beings can be supported on the
same area the more they diverge in structure, habits, and constitution,
of which we see proof by looking at the inhabitants of any small spot
or at naturalised productions. Therefore during the modification of the
descendants of any one species, and during the incessant struggle of all
species to increase in numbers, the more diversified these descendants
become, the better will be their chance of succeeding in the battle of
life. Thus the small differences distinguishing varieties of the same
species, will steadily tend to increase till they come to equal the
greater differences between species of the same genus, or even of
distinct genera.

We have seen that it is the common, the widely-diffused, and
widely-ranging species, belonging to the larger genera, which vary
most; and these will tend to transmit to their modified offspring
that superiority which now makes them dominant in their own countries.
Natural selection, as has just been remarked, leads to divergence of
character and to much extinction of the less improved and intermediate
forms of life. On these principles, I believe, the nature of the
affinities of all organic beings may be explained. It is a truly
wonderful fact--the wonder of which we are apt to overlook from
familiarity--that all animals and all plants throughout all time and
space should be related to each other in group subordinate to group,
in the manner which we everywhere behold--namely, varieties of the same
species most closely related together, species of the same genus less
closely and unequally related together, forming sections and sub-genera,
species of distinct genera much less closely related, and genera
related in different degrees, forming sub-families, families, orders,
sub-classes, and classes. The several subordinate groups in any class
cannot be ranked in a single file, but seem rather to be clustered
round points, and these round other points, and so on in almost endless
cycles. On the view that each species has been independently created, I
can see no exp