Lynn Margulis

American biologist

• Born: March 5, 1938; Chicago, Illinois
• Died: November 22, 2011; Amherst, Massachusetts

Lynn Margulis confirmed and expanded endosymbiotic theory by concluding that eukaryotic cells originated by a series of symbioses. Initially rejected by the scientific majority, her work on endosymbiotic theory was eventually accepted by the greater scientific community worldwide. She is remembered for collecting convincing evidence that symbiogenesis is a major factor of evolution leading to the origin of new species.

Primary field: Biology

Specialty: Evolutionary biology

Early Life

Lynn Margulis was born as Lynn Petra Alexander in Chicago, Illinois on March 5, 1938. She was the oldest of four girls born to Leona and Morris Alexander. A gifted student, Margulis enrolled at the University of Chicago at the age of fourteen, where she earned her bachelor’s degree in 1957. She then went to the University of Wisconsin–Madison, where she earned a master’s degree in zoology and genetics in 1960. Margulis then enrolled at the University of California, Berkeley, where she earned a PhD in genetics in 1965.

Margulis did her postdoctoral research at Brandeis University in Massachusetts. In 1965, she moved to Boston University, where she remained for over two decades before moving to the University of Massachusetts in Amherst, teaching botany as a faculty member in the department of geosciences.

In 1957, she married famous cosmologist Carl Sagan. The couple had two sons, Dorion and Jeremy. After Margulis and Sagan divorced, Margulis married chemist Thomas Margulis in 1967. The couple had a son, Zachary, and a daughter, Jennifer. Margulis and her second husband divorced in 1980.

Life’s Work

The work for which Margulis is best known is in the field of cellular biology. There are two fundamentally different types of cells studied in cellular biology: prokaryotic cells and eukaryotic cells. Prokaryotic cells do not have a nucleus or membrane-bound organelles, but eukaryotic cells possess both a nucleus and organelles. Bacteria and archaea (single-celled microorganisms) have the prokaryotic cell type, while all other types of organisms have eukaryotic cells. For many years, biologists have speculated about the ways in which complex eukaryotic cells first came to exist during evolution.

Russian biologist Konstantin S. Mereschkovsky had proposed one possible mechanism in 1905. According to Mereschkovsky, plant organelles known as chloroplasts originated in evolution when prokaryotic cyanobacterial cells invaded animal cells and began to live with a host cell in symbiotic coexistence. Mereschkovsky called his theory of the origin of chloroplasts “symbiogenesis,” which he described as “the origin of organisms through [the] combination of two or many beings, entering symbiosis.”

Another Russian biologist, Boris Kozo-Polyansky, extended Mereschkovsky’s symbiotic theory in his 1924 book A New Principle of Biology: An Essay on the Theory of Symbiogenesis. Kozo-Polyansky proposed that other organelles in eukaryotic cells, such as the mitochondria, Golgi complex, and nuclei, were also formerly free-living cells that developed symbiotic relationships with their host cells.

This theory of the symbiotic origin of eukaryotic cell organelles was forgotten until Margulis published “The Origin of Mitosing Eukaryotic Cells” in the Journal of Theoretical Biology in 1967. Before it was published, the paper was rejected by fifteen other journals. The majority of Margulis’s scientist contemporaries believed that cell organelles evolved by invasion of cell membranes, or by differentiation within the cell. Resurrecting the symbiotic theory, which she renamed “endosymbiotic theory,” exposed Margulis to enormous hostility within the scientific community. Nonetheless, she continued to pursue her work. During her tenure at Boston University, Margulis wrote a more detailed version of her endosymbiotic theory in her first book, Origin of Eukaryotic Cells (1970).

In Origin of Eukaryotic Cells, Margulis expanded the theory of the origin of the eukaryotic cell organelles and concluded that eukaryotic cells originated via a series of symbioses. This concept is known as serial endosymbiosis theory (SET). In subsequent years, data supporting symbiotic theory began to accumulate. For example, scientists found, as Margulis had predicted, that chloroplasts and mitochondria contain DNA similar to the DNA of certain bacteria. In 1981, Margulis published the extended version of her book entitled Symbiosis in Cell Evolution.

Margulis’s book was translated into several different languages. She traveled widely, presenting and defending the theory of symbiogenesis. Gradually, scientists began to accept the idea that primitive bacterial cells engulfed other small bacteria that began to live inside of the host and gradually entered into a symbiotic relationship. The process of symbiogenesis has become widely accepted.

To the symbiotic origin of chloroplast and mitochondria, Margulis added that flagella and cilia (appendages and protuberances that many microbes use for motility) originated from spiral bacteria called spirochetes. Additionally, in the second edition of her book Symbiosis in Cell Evolution (1993), she also introduced evidence that symbiogenesis is a major factor in evolution, leading to the creation of new species via natural selection. Margulis built on ideas first introduced by the Russian anarchist Peter Kropotkin in his book Mutual Aid: the Factor of Evolution (1902). Kropotkin had theorized that cooperation was as important in evolution as competition. Instead of opposing cooperation (symbiosis) and competition as Kropotkin did, Margulis reconciled symbiogenesis with the Darwinian theory of evolution. According to Margulis, symbiogenesis provides an evolutionary advantage to species.

Margulis is the author of numerous scientific articles and nine books, including Acquiring Genomes: A Theory of the Origins of Species (2002), and Dazzle Gradually: Reflections on the Nature of Nature (2007), cowritten with her son Dorian Sagan.

Margulis was a member of the National Academy of Sciences and the Russian Academy of Natural Sciences. She received the US president’s National Medal of Science, awarded by President Bill Clinton, and the Darwin–Wallace Medal of the Linnaean Society of London. In 1998, the Library of Congress in Washington, DC, announced that it would permanently archive her papers. She also won a prestigious Guggenheim fellowship. Margulis died on November 22, 2011 at the age of seventy-three.

Impact

Margulis is best known for developing ideas related to symbiogenesis, the theory of the symbiotic origin of organelles and eukaryotic cells. She theorized that eukaryotic cells developed from simple cells living in symbiosis with each other, over the course of evolution. Margulis’s work helped transform how evolution is understood by cellular biologists and the general scientific community. She challenged the widely held belief that random mutations in DNA are the main source of variation within populations. According to Margulis, new organelles, cells, and even new species evolve primarily through the fusion of genomes in symbioses, followed by the process of natural selection.

Many scientists have been inspired by Margulis’s work, including Russian biologist Michael V. Gusev, who studied the natural symbioses of Cyanobacteria and plants and the practical application of such symbioses. Margulis’s legacy also extended to W. Ford Doolittle of Dalhousie University in Canada, who studied ribosomal RNA molecules from Cyanobacteria and chloroplasts and found that they were similar.

During her career, some classic and forgotten articles and books on symbiogenesis were translated into English with Margulis’s encouragement. For example, a 1905 Mereschkovsky paper was translated from German into English by William Martin and Klaus Kowallik in 1999. In 2011, Boris Kozo-Polyansky’s 1924 work on symbiogenesis was translated from Russian into English and published, coedited by Margulis and zoologist Victor Fet.

Beyond Margulis’s contributions to the symbiogenesis theory and the theory of evolution, Margulis is acknowledged for her work with English scientist James E. Lovelock on his Gaia concept (named after an ancient Greek goddess representing the Earth). The Gaia theory argues that the Earth is a self-regulating ecosystem.

Bibliography

Graham, Linda E. and Lee W. Wilcox. Algae. Upper Saddle River: Prentice Hall, 2000. Print. Describes the origin of these groups during evolution by series of endosymbioses.

Kozo-Polyansky, Boris M. Symbiogenesis: A New Principle of Evolution. Ed. Victor Fet and Lynn Margulis. Harvard UP, 2010. Print. Reprint of Kozo-Polyansky’s 1924 book on symbiogenesis. Includes commentaries by Margulis regarding symbiotic theory.

Margulis, Lynn. Symbiosis in Cell Evolution. 2nd ed. New York: Freeman, 1993. Print. Introduces and explains the endosymbiotic theory of cell evolution.

Sagan, Lynn. “The Origin of Mitosing Eukaryotic Cells.” Journal of Theoretical Biology 14 (1967): 255–74. Print. Presents Margulis’s theory on the origin of eukaryotic cells.