Innumerable attempts have been made by fraud and force to procure cross breeds of different species of plants and animals, but always with the same result--the extinction of the progeny of the hybrid, unless bred back to nature.
While a mingling of various breeds of the same species--horses, sheep, or cattle--generally increases fertility, the attempt to mingle different species, as the horse and the ass, though so similar, always produces sterile offspring.

It is impossible to conceive any form in which the Creator could more emphatically protest against the attempt to confuse the distinctions of species He established.
God has fixed a barrier against the mixture or confusion of species by cross breeding, by ordaining the sterility of hybrids.

Mr.Darwin labors in vain to explain away this great fact.

It can not be explained into conformity with the evolution theory; for in that theory all species are only breeds or varieties of one species, and ought to increase their fertility by cross breeding.

With all scientific naturalists, as with all people of common sense, this proves that species have a distinct existence in nature, and that the Creator has ordained the continuance of their distinct existence; which is the denial of evolution.
When Mr.Darwin retreats into the geologic ages, and confessing that his principle has ceased to be operative now in our world, and refers us to them for such evolution of one species from another, he abandons the fundamental principle of his school--the uniformity of nature--and falls back on Christian ground the necessity for supernatural origins.