Tree of the living

That pleasing poster image of the whole history of terrestrial life contained within the form of a tree, which I happened on in the NYBG shop back in May, became a great teaching opportunity today. 

This pleasingly asymmetrical (but still upright) tree artfully arranges a great deal of information about the kinship of all of life, the relative age of different species, and how far back common ancestors of different kin may be found. A family tree! But this pretty image raises questions, too; it helped make salient the worry that tree diagrams "naturalize" a reality much more complex I'd started making Monday. I let the class figure it out on their own. 

The first observation was that trees - actual trees - are but a branch of this "tree of life." Was "life" tree-formed long before there were trees? One student suggested that the trees ought at least to be in the center, rather than Animalia - if not, another mused, the bacterial worlds which vastly exceed ours in number and mass... which led also to the belated realization that the tippy top of this big tree is not just an animal but a primate (a tree-dwelling one!). Is this yet another representation of us as the pinnacle of creation, the apex, the telos?

But these are just cosmetic problems. Eventually someone noticed that this image represents only "existing life." The five great extinctions are acknowledged if you look very closely - pale blue arcs - but it doesn't look like anything important got lost. History is written by the victors! But the history they write usually suggests they deserved or were destined to win, and this image does that too - precisely through its use of the tree as metaphor. Great tall trees famously grow from tiny seeds. The 3.8 billion year old "common ancestor" listed at bottom is like an acorn, which, the tree image suggests, already contained the whole tree before any of it grew, well, everything essential about it. Can it be true: Before trees were trees, we were already destined for the canopy.

Before I knew it, I was telling them about Stephen Jay Gould's book on the Burgess Shale, Wonderful Life, with its vertiginous sense that much more was lost in these extinctions than survived, and that the sheer contingency of which few did survive puts paid to the triumphalism of "survival of the fittest" neodarwinians, and should fill us with a kind of awe-filled humility at the gratuitousness of our own existence. What would a representation of the anything-but-preordained unfolding of life look like? A student obliged.

We'll get into the problems with even Darwin's tree soon. (Lateral gene transfer!) Maybe we can revere trees more truly in a shrubby world. But for today it was enough... we moved on to our reading, the first chapters of Haskell's The Songs of Trees, where no species is ever on its own, any "individual" actually a relationships among species.