Biologist Lynn Margulis is a professor at the University of Massachusetts Amherst. Probably her most important scientific contribution is the endosymbiotic hypothesis of the origin of mitochondria as separate organisms that long ago entered a symbiotic relationship with eukaryotic cells through endosymbiosis (see also symbiogenesis).
She is a proponent of the Gaia theory, based on an idea developed by the English atmospheric scientist James Lovelock. She was the first wife of Carl Sagan, and mother of Dorion Sagan.