CHAPTER XII

FACTORS OF ORGANIC EVOLUTION

Variation—Selection—Isolation—Spencer* s Contribution—
External Factors—Internal Factors—Direct Equili-
bration—Indirect Equilibration

DARWIN rendered three great services to evolution-
doctrine, (l) By his marshalling of the evidences
which suggest the doctrine of descent, he won the
conviction of the biological world. (2) He applied
the evolution-idea to various sets of facts, not only to
the origin of species in general, but to the difficult
case of Man; not only to the origin of the countless
adaptations with which organic nature is filled, but to
particular problems such as the expression of the
emotions 5 and in so doing he corroborated the
evolution-formula by showing what a powerful
organon it is. (3) Along with Alfred Russel "Wallace,
he elaborated the theory of natural selection, which
disclosed one of the factors in the evolution-process.

As we have seen, Herbert Spencer preceded
Darwin in his championing of the doctrine of descent,
to which the natural mood of his mind, and the
influences of Lamarck and von Baer had led him to
give his adhesion. He also applied the evolution-
formula to an even wider series of facts than Darwin
ventured to touch, viz., to the inorganic world and to
psychological and sociological facts. It remains to be
180 fact that, unlike the beasts that perish, man