My favorite bit from National Book Award finalist (and rightly so) and YA nonfiction title Charles and Emma: The Darwins' Leap of Faith:
They borrowed some novels from the library, starting a lifelong tradition of reading together--usually Emma read to Charles while he rested from his work. Charles liked novels with happy endings, and he once wrote, "I often bless all novelists. A surprising number have been read aloud to me . . . and I like all if moderately good, and if they do not end unhappily--against which a law ought to be passed. A novel, according to my taste, does not come into the first class unless it contains some person whom one can thoroughly love, and if it be a pretty woman all the better."
I say this book is not just a book for Darwinophiles, but for anyone who has ever been in the throes of a bookish romance.
Updated: A new report looks at the possible health repercussions of Charles and Emma being first cousins on their children.