Margulis’s discovery of endosymbiosis tells us something more about the history of life. Evolution is not just a matter of competition. Nor is it just a matter of constant divergence as new species appear. We also see collaboration, symbiosis, and even convergence. This means we have to reconsider the conventional metaphor of a tree of life, because even if we still think of three domains of life, it looks as if the third domain, the Eukarya, evolved not by increasing divergence but by the convergence of Archaea and Eubacteria—rather as if two branches of an ancient tree joined up again.
