The Origin of Species by means of Natural Selection, 6th Edition

Struggle for life most severe between individuals and varieties of the same species; often severe between species of the same genus. The relation of organism to organism the most important of all relations.

little doubt about many slight changes, such as size from the amount of food,

the first author who in modern times has treated it in a scientific spirit was Buffon

The only distinct meaning of the word 'natural' is STATED, FIXED or SETTLED; since what is natural as much requires and presupposes an intelligent agent to render it so, i.e., to effect it continually or at stated times, as what is supernatural or miraculous does to effect it for once."—Butler: "Analogy of Revealed Religion".

and so could not tell whether or not nearly perfect reversion had ensued.

aboriginal stock was,

we may safely conclude that very many of the most strongly marked domestic varieties could not possibly live in a wild state

that our domestic varieties, when run wild, gradually but invariably revert in character to their aboriginal stocks. H

I believe this rule to be of the highest importance in explaining the laws of embryology.

yet that it does tend to appear in the offspring at the same period at which it first appeared in the parent.