Saturday, October 15, 2011

Evolution is Not Simply Divergent

So I just wrote about how I enjoyed the little but formidable text Graphs Maps Trees, which applies scientific visualizations to literature. But there's a problems with the science, and once again, the trail for the misconception can be traced to Stephen Jay Gould.

Gould's point, repeated by Moretti, is that Darwin's original tree of life (yes, I know he was too smart to use that specific term, but it's what we call it now) was more to show divergence than simple common descent: in his diagram, only the most extreme branches continued from generation to generation, and he used to to account for species diversity. That's very true. Gould goes on to say (in a block quote in Moretti's essay) that evolution is a story of proliferation (this same branching of extremes), very different from cultural transmission in which an idea can be carried by a single human from one culture branch to another, and so the branches cross and weave and converge instead of just diverging.

The problem is that the real tree of life is indeed both convergent and divergent, like the cultural tree. The worst offender is this quote by a historian of technology, George Basalla:

"Different biological species usually do not interbreed, and on the rare occasions when they do their offspring are infertile. Artifactual types, on the other hand, are routinely combined to produce new and fruitful entities" (p.137). a.) e.g., the internal combustion engine was merged with the bicycle & the horse-drawn carriage to produce the automobile (p.138)

Um, no. As a biochemist looking at the tree of life, I see exactly this same repurposing of old parts and combinations to make new parts everywhere. Even the process of making antibodies is a shuffling of old parts to make something new. Basalla's quote only works for a limited set of macroscopic species, and I think it's the exception rather than the rule. Bacteria trade genes and build new things by combination all the time. Just because a mule is infertile doesn't mean convergence never happens.

This is a major point of the argument, and it actually helps Moretti, because he's arguing that convergence is the normal state of affairs in literature, and I'm happy to say I think it's the normal state of affairs in science as well. Conway Morris and Dawkins agree with me on this. Fascinatingly on p.81 Moretti argues that if divergence is king then randomness is running the show, but in human affairs like literature, convergence is dominant. Since I'm arguing that convergence is the characteristic of all evolution, then am I arguing that the ecosystem is more "human" than we may have thought? A provocative phrase, and I'm content to think about it for now.

True, the branches of the tree of life can never fully converge, but they can functionally converge. Moretti points out on p.85 that the branches of the tree of literature can never fully converge either, but always remain distinct. The more we talk the more I think we're basically talking about the same kind of tree.

In a nice summary of the branching diagram for literature, Moretti concludes that "literature moves forwords and sideways at once; often, more sideways than forwards. Like Shklovsky's great metaphor for art, the knight's move at chess." (p. 91) Do DNA trees of life imply that life makes similar knight's moves?

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