The Song of the Dodo
by David Quammen. Great look at evolution, touching, of course, quite a bit on Charles Darwin and Alfred Wallace- who developed the theory independently.
I also really enjoy a book called The Control of Nature
by John McPhee. Three stories about how humans are resisting natural geologic forces, like the natural tendency of a river system to change it's course (in this case, the Mississippi trying to shift into the Atchfalaya).