New York Times: In 1837, Charles Darwin opened a notebook and drew a simple tree with a few branches. Each branch, which he labeled with a letter, represented a species. In that doodle, he captured his newfound realization that species were related, having evolved from a common ancestor. Across the top of the page he wrote, “I think.” Two decades later Darwin presented a detailed account of the tree of life in “On the Origin of Species.” And much of evolutionary biology since then has been dedicated to illuminating…

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