Lynn Margulis

Lynn Margulis was an American evolutionary biologist who championed the idea that symbiosis—organisms living together—is a major driver of evolution. She is best known for reshaping how scientists think about the origin of eukaryotes, the group of organisms whose cells have a nucleus. Her central claim was that these complex cells evolved when different types of bacteria merged and began living inside one another.

Born Lynn Petra Alexander in Chicago in 1938, she was the oldest of four daughters. Her father was a lawyer who also ran a road-paint company, and her mother owned a travel agency. She described herself as a poor student in high school, often sent to stand in the corner. At fifteen, she was accepted into the University of Chicago Laboratory Schools, and at nineteen she earned a bachelor’s degree in liberal arts from the University of Chicago. She went on to the University of Wisconsin, where she studied under Hans Ris and Walter Plaut, earning a master’s degree in genetics and zoology in 1960. Her first scientific paper, co-authored with Plaut, was on the genetics of *Euglena*, a flagellate with both animal and plant traits. She then began research at the University of California, Berkeley, under zoologist Max Alfert. Before finishing her dissertation, she took a research associateship and then a lectureship at Brandeis University in 1964. While there, she completed her PhD from Berkeley in 1965, with a thesis on thymidine incorporation in *Euglena*.

In 1966, Margulis moved to Boston University, where she taught biology for twenty-two years. She started as an adjunct assistant professor, became an assistant professor in 1967, associate professor in 1971, full professor in 1977, and university professor in 1986. In 1988, she became a distinguished professor of botany at the University of Massachusetts Amherst, and in 1993 a distinguished professor of biology. In 1997, she moved to the geosciences department there, a post she held until her death.

Her landmark paper, “On the Origin of Mitosing Cells,” was written in 1966 but rejected by about fifteen journals before finally appearing in the *Journal of Theoretical Biology* in 1967. In it, she argued that organelles like mitochondria and chloroplasts were once free-living bacteria. The idea was largely ignored for another decade. It gained wide acceptance only after genetic evidence—showing that the DNA of mitochondria and chloroplasts is very different from nuclear DNA—was confirmed in the early 1980s. Experimental proof that mitochondria descended from bacteria and chloroplasts from cyanobacteria came in 1978 from Robert Schwartz and Margaret Dayhoff. Richard Dawkins later praised Margulis for her courage and persistence in turning the endosymbiosis theory from an unorthodox idea into an accepted one.

Margulis also co-developed the Gaia hypothesis with chemist James Lovelock, which proposes that Earth acts as a single, self-regulating system. She was a strong defender of Robert Whittaker’s five-kingdom classification of life. She was a vocal critic of neo-Darwinism, which led to lifelong debates with prominent biologists such as Richard Dawkins, George C. Williams, and John Maynard Smith. Her work had important predecessors dating back to the mid-19th century, including Andreas Franz Wilhelm Schimper, Konstantin Mereschkowski, Boris Kozo-Polyansky, and Ivan Wallin. Margulis not only promoted their contributions but also oversaw the first English translation of Kozo-Polyansky’s book *Symbiogenesis: A New Principle of Evolution*, published the year before she died. Many of her popular books were co-written with her son, Dorion Sagan.

Margulis was elected to the U.S. National Academy of Sciences in 1983. President Bill Clinton awarded her the National Medal of Science in 1999. The Linnean Society of London gave her the Darwin-Wallace Medal in 2008. In 2002, *Discover* magazine named her one of the 50 most important women in science. She died on November 22, 2011.