ng through a
series of changes something more complex, or at least different, has come
into being. To lump all these kinds of changes into one and call them
evolution is no more than asserting that you believe in consecutive series
of events (which is history) causally connected (which is science); that
is, that you believe in history and that you believe in science. But let us
not forget that we may have complete faith in both without thereby offering
any explanation of either. It is the business of science to find out
_specifically_ what kinds of events were involved when the stars evolved in
the sky, when the horse evolved on the earth, and the steam engine was
evolved from the mind of man.

Is it not rather an empty generalization to say that any kind of change is
a process of evolution? At most it means little more than that you want to
intimate that miraculous intervention is not necessary to account for such
kinds of histories.

We are concerned here more particularly with the biologists' ideas of
evolution. My intention is to review the evidence on which the old theory
rested its case, in the light of some of the newer evidence of recent
years.

Four great branches of study have furnished the evidence of organic
evolution. They are:

Comparative anatomy.
Embryology.
Paleontology.
Experimental Breeding or Genetics.

_The Evidence from Comparative Anatomy_

When we study animals and plants we find that they can be arranged in
groups according to their resemblances. This is the basis of comparative
anatomy, which is only an accurate study of facts that are superficially
obvious to everyone.

The groups are based not on a single difference, but on a very large number
of resemblances. Let us take for example the group of vertebrates.

[Illustration: FIG. 3. Limb skeletons of extinct and living animals,
showing the homologous bones: 1, salamander; 2, frog; 3, turtle; 4,
Aetosaurus; 5, Pleisiosaurus; 6, Ichthyosaurus; 7, Mesosaurus; 8, duck.
(After Jordan and Kellogg.)]

The hand and the arm of man are similar to the hand and arm of the ape. We
find the same plan in the forefoot of the rat, the elephant, the horse and
the opossum. We can identify the same parts in the forefoot of the lizard,
the frog (fig. 3), and even, though less certainly, in the pectoral fins of
fishes. Comparison does not end here. We find similarities in the skull and
back bones of these same animals; in the brain; in the dig