er the conditions given at a given time. During the
period of development of worms and lower vertebrates much muscle
with a little brain was more useful than more brain with less
muscle. Hence, as a rule, the more muscular survived; the brain
increasing slowly, at first apparently largely because of its
correlation with muscle and sense-organs. At a later date muscle,
tooth, and claw were more useful on the ground; brain and hand in
the trees. Hence carnivora ruled the ground, and certain arboreal
apes became continually more anthropoid. At a later date brain
became more useful even on the ground, and was marked on a higher
scale, because it could invent traps and weapons against which
muscle was of little avail. Just at present brain is of use to, and
valued by, a large portion of society in proportion to its
efficiency in making and selfishly spending money. 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.' As
fast as the faculties are multiplied, so fast does it become