The occurrence of such places will often depend on physical
changes, which generally take place very slowly, and on the immigration of
better adapted forms being prevented. As some few of the old inhabitants
become modified the mutual relations of others will often be disturbed; and
this will create new places, ready to be filled up by better adapted forms;
but all this will take place very slowly. Although all the individuals of
the same species differ in some slight degree from each other, it would
often be long before differences of the right nature in various parts of
the organisation might occur. The result would often be greatly retarded
by free intercrossing. Many will exclaim that these several causes are
amply sufficient to neutralise the power of natural selection. I do not
believe so. But I do believe that natural selection will generally act
very slowly, only at long intervals of time, and only on a few of the
inhabitants of the same region. I further believe that these slow,
intermittent results accord well with what geology tells us of the rate and
manner at which the inhabitants of the world have changed.
Slow though the process of selection may be, if feeble man can do much by
artificial selection, I can see no limit to the amount of change, to the
beauty and complexity of the coadaptations between all organic beings, one
with another and with their physical conditions of life, which may have
been effected in the long course of time through nature's power of
selection, that is by the survival of the fittest.
Pages:
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187