QUOTE: "Today, the argument over where eukaryotes came from has matured. Many on both sides agree that the origin of eukaryotes probably involved a step known as endosymbiosis. This theory, championed by the late biologist Lynn Margulis, holds that a simple host cell living eons ago somehow swallowed a bacterium, and the two struck up a mutually beneficial relationship. These captive bacteria eventually evolved into mitochondria — the cellular substructures that produce energy — and the hybrid cells became what are now known as eukaryotes."

dhw: Just in passing, it is worth noting that Lynn Margulis regarded cooperation as a major factor in evolution, and championed the cause of cellular intelligence.

Lynn Margulis was a brilliant scientist. She was married to Carl Sagan.