Several years ago, Alan Gribben informed me that Twain's collection of Darwin's books was housed in the library at Wake Forest. Since I work at Wake Forest, I went to the special collections section to look at the books in person, and to look at the marginalia (all of which had been thoroughly documented by Alan's work). As most subscribers to this list know, one of Twain's famous aphorisms was derived from Darwin's writing. I had an experience that made the aphorism extremely applicable, and wrote an essay about the book, the marginalia, and the aphorism.
Pat Ober
http://www.wakehealth.edu/Oasis/A-NEED-TO-BLUSH.htm