Monday, March 25, 2024

Tree of extinction


As I'm trying to wrangle the many many contexts in which one reads of a "tree of life" into one argument, I decided, on a whim, to search for "tree of extinction." (Part of my argument, as you know, is that Charles Darwin was drawn to the tree as a model for the history of species precisely because trees naturally lose many branches.) 

Something came up! The article, just half a year old, is "Mutilation of the tree of life via mass extinction of animal genera," and it argues that we are already well into the sixth extinction. Whole genera of animals have gone extinct in recent centuries, at a far swifter rate than before and much too quickly for evolution to fill the gaps. And many more are at risk. It's a powerful, urgent argument, but the accompanying illustration undermines it. 

With images of extinct genera on the withered branches, it sort of corresponds to Darwin's tree of life, which includes extinct as well as living species. But their point is not that this is business as usual. We're supposed to imagine that the same fate may await the genera represented in the green canopy above. Where the image undermines their argument is that the tree in the picture looks perfectly healthy. We expect the lower part of the trunk of a tree to be branchless. And if higher branches die off, too, we expect that that's just part of the tree's growing higher still, generating a new canopy.