This is the way in which all our fine garden fruits and
vegetables and flowers have been produced, as well as all our splendid
breeds of domestic animals; and they have thus become in many cases so
different from the wild races from which they originally sprang as to be
hardly recognisable as the same. It is therefore proved that if any
particular kind of variation is preserved and bred from, the variation
itself goes on increasing in amount to an enormous extent; and the
bearing of this on the question of the origin of species is most
important. For if in each generation of a given animal or plant the
fittest survive to continue the breed, then whatever may be the special
peculiarity that causes "fitness" in the particular case, that
peculiarity will go on increasing and strengthening _so long as it is
useful to the species_. But the moment it has reached its maximum of
usefulness, and some other quality or modification would help in the
struggle, then the individuals which vary in the new direction will
survive; and thus a species may be gradually modified, first in one
direction, then in another, till it differs from the original parent
form as much as the greyhound differs from any wild dog or the
cauliflower from any wild plant.
Pages:
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44