Well, as I am desperately trying to prevent Hollywood from corrupting the term "Tree of Life" and I got to thinking. Why did Darwin and others have to use the metaphor of a tree to represent the branching history of organisms through evolutionary time? Why did other metaphors not get used? Well, thanks to a little research I did by communicating with Darwin directly (as I did when he announced his endorsement of Obama), I have found out that Darwin went through many other metaphors before settling on the "Tree of Life." (note the tree-like figure here which is based on the one figure in the Origin of Species).
And here are the top 5 other such metaphors for what is now known as "The Tree of Life"
- The coral of life. Darwin particularly liked this one as he did some work on marine organisms. But ultimately he rejected it because he was worried about anti-evolutionists killing coral to get back at Darwin.
- The watershed of life. Rivers exhibit branching patterns much like trees. The big problem Darwin saw was that sometimes separate river branches reconnect to each other, which did not follow his model for descent. If only Darwin knew about lateral gene transfer.
- The blood vessels of life. Darwin was desperate to find visceral connections for people to evolution. This one would have been great. The big problem here was the "going" and "coming" nature of arteries and veins.
- The shrub of life. Thus turns out to have been one of Darwin's favorites because it captures the richness of diversity more than a sparsely branching tree. However, shrub, even then, was used as a derogatory term to refer to height challenged individuals. And Darwin did not want to upset this key constituency so he avoided this term.
- The lungs of life. While this has some positive features (e.g., it is unidirectional like a tree), thankfully Darwin did not stick to this or we would have competition from "LOL" for all the domain names.
Other possibilities included "the Plumbing System of Life" and "the Highway Map of Life". If you know of others Darwin may have considered, let me know.