But which groups will ultimately
prevail, no man can predict; for we well know that many groups,
formerly most extensively developed, have now become extinct. Looking
still more remotely to the future, we may predict that, owing to the
continued and steady increase of the larger groups, a multitude of
smaller groups will become utterly extinct, and leave no modified
descendants; and consequently that of the species living at any one
period, extremely few will transmit descendants to a remote futurity.
I shall have to return to this subject in the chapter on
Classification, but I may add that on this view of extremely few of
the more ancient species having transmitted descendants, and on the
view of all the descendants of the same species making a class, we can
understand how it is that there exist but very few classes in each
main division of the animal and vegetable kingdoms. Although extremely
few of the most ancient species may now have living and modified
descendants, yet at the most remote geological period, the earth may
have been as well peopled with many species of many genera, families,
orders, and classes, as at the present day.
SUMMARY OF CHAPTER.
If during the long course of ages and under varying conditions of
life, organic beings vary at all in the several parts of their
organisation, and I think this cannot be disputed; if there be, owing
to the high geometrical powers of increase of each species, at some
age, season, or year, a severe struggle for life, and this certainly
cannot be disputed; then, considering the infinite complexity of the
relations of all organic beings to each other and to their conditions
of existence, causing an infinite diversity in structure,
constitution, and habits, to be advantageous to them, I think it would
be a most extraordinary fact if no variation ever had occurred useful
to each being's own welfare, in the same way as so many variations
have occurred useful to man.
Pages:
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165