Word: tree
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...then fallen back down to earthly obscurity with the nose-bleeding steepness of Barthelme. In the 1970s, he was considered the future of literature, and he still has fanatical supporters, my family being Exhibit A. But mostly he's regarded as a dead, twisted branch on the evolutionary tree of American letters. The first major biography of him, Tracy Daugherty's Hiding Man (St. Martin's; 581 pages), should help correct that...
Darwin had no way of knowing this, since he had no way of examining DNA. If he did, he might well have rethought one of his most potent metaphors for evolution: the tree of life. It's not that the metaphor is wrong. Scientists regularly reconstruct evolutionary branches today. When a new disease breaks out, for example, the fastest way to figure out what to do is to determine what the pathogen is related...
...there's more to the history of life than the branching of a tree. Every now and then, DNA moves between species. Viruses ferry genes from one host to another. Bacteria swap genes inside our bodies, evolving resistance to antibiotics in our own gut. Some 2 billion years ago, one of our single-celled ancestors took in an oxygen-consuming bacterium. That microbe became the thousands of tiny sacs found in each of our cells today, known as mitochondria, that let us breathe oxygen. When genes move this way, it's as if two branches of the tree of life...
...dirt, twice as many species as all the mammals in the world. In the genome of a typical microbe, most of the genes hopped from one species to another at some point in the history of life. In some ways, the history of life is indeed like a tree, sprouting new branches. But in some ways, it's also like a tapestry, emerging from a loom, its genetic threads woven together in new combinations...
...pictures of Barack Obama's family tree...