Today, as you probably know, is Darwin's 200th birthday. It is well worth raising a glass to a man who had "the best idea in history", but a little footnote to the story has been this image:
A page from his notebooks in which he, tentatively and endearingly, outlines the concept of a “tree of life”. What intrigues me about this notebook entry is the importance of visual thinking and doodling in getting complex ideas down on paper. Darwin starts with “I think” and then gives up on words—drawing the concept is much easier and clearer. The same fundamental tool is still used in cladistics to this day.
The diagram is backed up by some more text
“Case must be that one generation then should be as many living as now. To do this & to have many species in same genus (as is) requires extinction.
Thus between A & B immense gap of relation. C & B the finest gradation, B & D rather greater distinction. Thus genera would be formed. — bearing relation”
The combination of diagram and words (written or spoken) is often the best way to think through ideas, and to communicate them to others. If your visual thinking is a bit rusty I'd recommend Dan Roam's The Back of the Napkin. Despite the slightly lukewarm review I gave it back in December it really is a valuable read.