The most important evidence for endosymbiosis is the odd fact that some of the organelles inside eukaryotes contain their own DNA, and that DNA is quite different from the genetic material in the nucleus. Margulis realized that organelles such as the mitochondria that manage energy in animals and the chloroplasts that manage photosynthesis in eukaryotic plants look as if they were once independent prokaryotic cells. Exactly how they ended up inside other cells remains unclear, and some have argued that such mergers must be extremely rare. If so, that probably means that even if bacterialike
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