Lynn Margulis (born Lynn Petra Alexander; March 5, 1938 – November 22, 2011) was an American evolutionary theorist, taxonomist, bacteriologist, protistologist, and botanist, with advanced degrees in zoology and genetics. She was known to the public as a science author, educator, and popularizer, and recognized as the primary modern proponent for the significance of symbiosis in biological evolution. Historian Jan Sapp has noted that, "Lynn Margulis’s name is as synonymous with symbiosis as Charles Darwin’s is with evolution." In particular, Margulis transformed and fundamentally framed current understanding of the evolution of cells with nuclei – an event Ernst Mayr called "perhaps the most important and dramatic event in the history of life" – by proposing it to have been the result of symbiotic mergers of bacteria. Margulis was also the co-developer of Gaia theory with the British chemist James Lovelock, proposing that the Earth functions as a single self-regulating system, and was the principal defender and promulgater of the five kingdom classification of Robert Whittaker.