It is not the biggest, the brightest or the best that will survive, but those who adapt the quickest.

Among the scenes which are deeply impressed on my mind, none exceed in sublimity the primeval [tropical] forests, ... temples filled with the varied productions of the God of Nature. No one can stand in these solitudes unmoved, and not feel that there is more in man than the mere breath of his body.

Why, if species have descended from other species by insensibly fine gradations, do we not everywhere see innumerable transitional forms.

Animals manifestly enjoy excitement, and suffer from annul and may exhibit curiosity.

I am a firm believer, that without speculation there is no good and original observation.

It is not the biggest, the brightest or the best that will survive, but those who adapt the quickest.

After five years' work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions, which then seemed to me probable: from that period to the present day I have steadily pursued the same object. I hope that I may be excused for entering on these personal details, as I give them to show that I have not been hasty in coming to a decision.‎