This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.

I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am convinced that natural selection has been the most important, but not the exclusive, means of modification.

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.

I think it inevitably follows, that as new species in the course of time are formed through natural selection, others will become rarer and rarer, and finally extinct. The forms which stand in closest competition with those undergoing modification and improvement will naturally suffer most.

Farewell Australia! You ... are too great and ambitious for affection, yet not great enough for respect. I leave your shores without sorrow or regret.

Embryology will reveal to us the structure, in some degree obscured, of the prototypes of each great class.