Darwin or Lincoln?

I just read the article "Who Was More Important: Lincoln or Darwin?". I know very little about American history but I am very interested in reading more about Darwin. Last week I read an article in National Geographic about Alfred Russel Wallace, Darwin's fellow naturalist who also came up with the idea of evolution, but failed to publish before Darwin did.

Apparently On the Origin of Species is a very readable book, even if it's a scientific treatise. It's on my list of books to read.

Also to read (maybe): historian David R. Contosta's "Rebel Giants", that sets forth biographical parallels between Darwin and Lincoln.