Cannibal's relief:  the origins of sex.
Microorganisms in the gut of a cockroach resemble those that lived on earth 2000 million years ago.  One of their activities, eating each other, may hold the key to the history of sexual reproduction in today's animals and plants.
Sagan
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Margulis
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D000818:Animals; D018407:Bacterial Physiological Phenomena; D005075:Biological Evolution; D002190:Cannibalism; D002468:Cell Physiological Phenomena; D003227:Conjugation, Genetic; D004247:DNA / Q000502:physiology; D005306:Fertilization / Q000235:genetics / Q000502:physiology*; D008540:Meiosis / Q000235:genetics / Q000502:physiology*; D008938:Mitosis / Q000235:genetics / Q000502:physiology*; D011235:Predatory Behavior; D012098:Reproduction / Q000502:physiology*; D012100:Reproduction, Asexual / Q000502:physiology; D012723:Sex
D004247:DNA