more ancient species, and so on. The human races, upon this view, likewise
may or may not be species according to the notions of each naturalist as to
what differences are specific; but, if not species already, those races that
last long enough are sure to become so. It is only a question of time.

How well the simile of a genealogical tree illustrates the main ideas of
Darwin's theory the following extract from the summary of the fourth
chapter shows:

"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 explanation of this great fact
in the classification of all organic beings; but, to the best of my
judgment, it is explained through inheritance and the complex action of
natural selection, entailing extinction and divergence of character, as we
have seen illustrated in the diagram.

"The affinities of all the beings of the same class have sometimes been
represented by a great tree. I believe this simile largely speaks the truth.
The green and budding twigs may represent existing species; and those
produced during each former year may represent the long succession of