That climate acts in main part indirectly by favouring other species, we clearly see in the prodigious number of plants which in our gardens can perfectly well endure our climate, but which never become naturalised, for they cannot compete with our native plants nor resist destruction by our native animals.

I believe that animals have descended from at most only four or five progenitors, and plants from an equal or lesser number.

The young and the old of widely different races, both with man and animals, express the same state of mind by the same movements.

Judging from the past, we may safely infer that not one living species will transmit its unaltered likeness to a distant futurity.

It is not that these countries, so rich in species, do not by a strange chance possess the aboriginal stocks of any useful plants, but that the native plants have not been improved by continued selection up to a standard of perfection comparable with that given to the plants in countries anciently civilised.

Species that struggle to adapt to survive will become extinct.