Hence it follows that the separation of animals
into orders and genera and even into species took place, if not for the
most part yet very largely, at a very early period in the history of
organic evolution. Of course the descendants of any one of the original
vertebrata might, and probably in not a few cases did, branch off into
new subdivisions and yet again into further subdivisions, and we are
always justified in looking for unity of ancestry among all the species.
But it is also quite possible that any species may be regularly
descended, without branching off at all, from one of the originals, and
that other species that resemble it may owe the resemblance simply to
very great similarity of external conditions. To find, for instance, the
unity of ancestry between man and the other animals, it will certainly
be necessary to go back to a point in the history of life when living
creatures were as yet formless, undeveloped--the materials, as we may
call them, of the animal creation as we now see it, and not in any but a
strictly scientific sense, what we mean when we ordinarily speak of
animals. The true settlement of such questions as these can only be
obtained when long and patient study shall have completed Darwin's
investigations by determining under what laws and within what limits the
slight variations which characterise each individual animal or plant are
congenitally introduced into its structure.
Pages:
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154