But slowly and
surely it is becoming of use as an organ of thought, for the sake of
the truth which it can discover and incarnate.
Natural selection works thus apparently for the survival of the
individuals possessing in the aggregate the most complete conformity
to environment. Let us now imagine that an animal is so constructed
as to be capable of variation along several disadvantageous or
neutral lines, and along only one which is advantageous. The
development would of course proceed along the advantageous line. Let
us farther imagine that to the descendants of this individual two,
and only two, advantageous lines of variations are allowed by its
structure. Then natural selection would probably favor the decidedly
advantageous line, if such there were. But as long as the structure
of the animal allows variation along only a few lines, the
two advantageous variations would, according to the law of
probabilities, frequently occur in the same individual. The eggs and
spermatozoa of two such individuals might not infrequently unite,
and thus in time the two characteristics be inherited by a large
fraction of the species.
And now let me quote from Mr. Spencer:
"But in proportion as the life grows complex--in proportion as a
healthy existence cannot be secured by a large endowment of some
one power, but demands many powers; in the same proportion do
there arise obstacles to the increase of any particular power, by
'the preservation of favored races in the struggle for life.
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