I had the opportunity yesterday to visit Boston's Museum of Science & there were two special treats in store for me. First, a magnificent display of the late Bradford Washburn's mountain photography. Right next door was an exhibit on the life and impact of Charles Darwin.
The Darwin exhibit focuses on his life but also touches on why his theory is so central to modern biology. There are some of his actual notebooks (of facsimiles). On one of these, I believe an original, is the first evolutionary tree -- a sketch by Darwin early in his contemplations. At the top, in jubilant exclamation, is "I think!". What an understatement!