Addison said, “The real substance of a bulky volume can be condensed
into a small pamphlet.”; and it is believed that the fundamental
principles of a great scientific discovery like evolution can be
outlined in a few pages, and in a way so plain and in words so
simple that any one who is at all interested can get a fairly good
understanding of its scope. With this idea in mind an attempt is here
made to explain evolution, to tell what some of its laws are and how
they work, and to present briefly some of the evidences that support
the doctrine.
Contrary to popular belief evolution is not confined to the origin of
man, but it explains how all living things have become as we now see
them, and how and why the most of them are being changed. It teaches
that all living species of plants and animals, including man, also
the thousands of extinct species which have left their fossil records
in stratified rocks, have been developed from a few small and simple
forms--probably one, and that a mere cell. And it shows, too, that this
has been done by the operation of natural laws, the same laws we see in
operation today.
Evolution does not teach that every living thing is “day by day, in
every way, growing better and better.” On the contrary, it shows that
many species deteriorate, are driven to the wall and become extinct,
while only the best fitted survive. For instance, of the twenty-five
orders of reptiles in the Jurassic period--known to the geologists by
their fossils--only five have come down to our times. But out of the
reptilian orders, then the highest forms of living things, have come
the superior orders of later times--birds and mammals. And this is
evolution.
We sometimes hear the statement that scientists are not in agreement
in regard to evolution. The point of disagreement is in respect to the
part played by natural selection in the development of species, and not
as to whether or not evolution is a fact. The discussion is in regard
to the _how_ of the fact and not the fact itself. No great scientist
since Agassiz, who died in 1873, has opposed evolution.
Neither does evolution teach that one species may develop into
another, as that the goat may develop into the deer, or that the ape
may evolve into man. For one species to become another existing species
it would have to take the back track to the point where the two species
began to diverge and travel the other route--which of course would be
impossible. This may help in getting the idea: the larger divisions and
groups of animals (fishes, reptiles, mammals, etc.) may be compared
to the main or primary branches of a tree, the families and orders
(as the deer, the cat, and the dog) to the secondary branches growing
from the primary ones, and the species to the further divisions of
the secondary branches. Now we can see that one species can no more
become another--that is, any now existing--than one branch of a tree
can become another. A species can, in time, if subject to the proper
conditions, split into varieties which, if developed far enough, may
become distinct species. But no one of these species can be said to
have been evolved from a contemporary species, for all have been
changed, and the stock from which they came has ceased to exist as
such. Each of the existing species would have a distinct name such
as, for instance, cow, bison, Cape buffalo, yak. Now suppose the
fossil remains of the common ancestor of the above-named species were
found--what should it be called, cow, bison, Cape buffalo, or yak? It
would be neither, for it would probably differ as much or more from
them as they differ among themselves. Thus is laid to rest the idea
that evolution is a theory that man was evolved from, or by way of, the
monkey or the ape. They are as distinct species as is man himself.