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 extinct species. At each period of growth all the
growing twigs have tried to branch out on all sides, and to overtop
and kill the surrounding twigs and branches, in the same manner as
species and groups of species have tried to overmaster other species
in the great battle for life. The limbs divided into great branches,
and these into lesser and lesser branches, were themselves once, when
the tree was small, budding twigs; and this connexion of the former
and present buds by ramifying branches may well represent the
classification of all extinct and living species in groups subordinate
to groups.
Pages:
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168