I am actually weary of telling people that I do not pretend to adduce [direct] evidence of one species changing into another, but I believe that this view is in the main correct, because so many phenomena can thus be grouped end explained.

It is a fatal fault to reason whilst observing, though so necessary beforehand and so useful afterwards.

Daily it is forced home on the mind of the biologist that nothing, not even the wind that blows, is so unstable as the level of the crust of this earth.

I long to set foot where no man has trod before.

... not one living species will transmit its unaltered likeness to a distant futurity.

Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult--at least I have found it so--than constantly to bear this conclusion in mind.

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