We examine the Tree of Life (TOL) as an evolutionary hypothesis and a heuristic. The original TOL hypothesis has failed but a new "statistical TOL hypothesis" is promising. The TOL heuristic usefully organizes data without positing fundamental evolutionary truth.
This article was reviewed by W. Ford Doolittle, Nicholas Galtier and Christophe Malaterre.
"And after a while you'll hear a deep voice saying, "Neighbor, how stands the Union?" Then you better answer the Union stands as she stood, rock-bottomed and copper sheathed, one and indivisible, or he's liable to rear right out of the ground."
The Devil and Daniel Webster (Stephen Vincent Benet, 1937)
"On a huge hill,
Cragged, and steep, Truth stands, and he that will
Reach her, about must and about must go"
Satire III (John Donne, written 1593-1600)
Looking back to go beyond the Tree of Life
One might think that there is nothing further that could be said about the last decades of debate on the Tree of Life (TOL). There is certainly no need to recapitulate the numerous overviews of these debates as they set out the positions of key participants (e.g.,[1-3]). However, as the pageantry of 2009's "Darwin Year" subsides, it seems to be an appropriate time to reflect on where TOL studies are headed in relation to the legacies on which they draw. We will consider two key issues: the specific effects of these debates on the conceptual frameworks of TOL studies, and how these frameworks are actually used. We will discuss whether they function as hypotheses or heuristics. To put it in a deliberately over-simplified way, it seems useful to examine two basic questions:
• What are reasonable interpretations of the TOL in the postgenomic era?
• What is the utility of the TOL for research in evolutionary biology and perhaps beyond?