Lynn Margulis (US) is an evolutionary biologist who introduced the endosymbiosis theory - evolution by symbiosis.
Lynn Margulis is an evolutionist and cell biologist, who in the 1970s, helped advance the study of the origins of cells by developing the 'symbiotic theory', stating that life on Earth developed through symbiosis.
Symbiosis, in Margulis' words, is a physical association between organisms, where species form new composite entities by fusion and merger. The proof being, that aside from the nuclear DNA (human genome), each of us also has mitochondrial DNA, which is a different lineage, inherited through our mothers.
Thus, in every fungus, animal, or plant (and in most protoctists), at least two distinct genealogies exist side by side. This is a clue that at some point these organelles were distinct microorganisms that joined forces. In essence, new organelles, tissues, organs, and even new species evolve primarily through the fusion of genomes in symbioses followed by natural selection (making Margulis a Darwinist - but not a neo-Darwinist).
A holistic view associated her with James Lovelock and his Gaia hypothesis, which posits that the Earth’s surface interactions among living beings in sediment, air, and water have created a vast self-regulating system. Thus, earth can be seen as a single self-regulating organism, a complex entity whose living and inorganic elements are interdependent and whose life-forms actively modify the environment to maintain hospitable conditions.
Lynn Margulis is Distinguished University Professor in the Department of GeoSciences at the University of Massachusetts, Amherst. From 1977 to 1980, she chaired the National Academy of Science's Space Science Board Committee on Planetary Biology and Chemical Evolution to aid in developing research strategies for NASA. She was elected to the National Academy of Sciences in 1983, and is one of three American members of the Russian Academy of Natural Sciences. In 1999, she received the President's National Medal of Science in Biological Sciences, and the William Procter Prize of Sigma Xi, an international research society. In 2008 she received the Darwin-Wallace Medal of the Linnean Society of London. Her publications span a wide-range of scientific topics, but are mainly on cell biology and microbial evolution.