In the Origin of Species, Darwin described a “great Tree of Life” which is “fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.”
Ever since then biologist have been trying to describe such a tree. And it should surprise no one that the recent focus on microbial ecology has expanded the Tree considerably.
Read about it at the New York Times or in the paper over at Nature Microbiology .