Though nature grants vast periods of time for the work of natural selection, she does not grant an indefinite period; for as all organic beings are striving, it may be said, to seize on each place in the economy of nature, if any one species does not become modified and improved in a corresponding degree with its competitors, it will soon be exterminated.

This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection, or the Survival of the Fittest.

Natural Selection almost inevitably causes much Extinction of the less improved forms of life and induces what I have called Divergence of Character.

Natural selection acts solely by accumulating slight successive favorable variations, it can produce no great or sudden modification; it can act only by very short steps.

Man could no longer be regarded as the Lord of Creation, a being apart from the rest of nature. He was merely the representative of one among many Families of the order Primates in the class Mammalia.

He who is not content to look, like a savage, at the phenomena of nature as disconnected, cannot any longer believe that man is the work of a separate act of creation ... Man is the co-descendant with other mammals of a common progenitor.