Lynn Margulis

Lynn Margulis (1938–2011) was an American evolutionary biologist who developed the modern theory that mitochondria and chloroplasts originated as free-living bacteria incorporated into ancestral cells.

Carl Woese: An American microbiologist who established the three-domain system of life using molecular comparisons of ribosomal RNA. His classification of archaea and bacteria helped establish the microbial evolutionary context for Margulis’s work.
Endosymbiotic theory: The theory that some organelles originated when ancestral cells incorporated free-living bacteria that persisted as symbionts. This is the central evolutionary explanation Margulis argued for and helped establish.
Symbiogenesis: Evolutionary change in which new biological forms arise through the lasting association or merger of distinct organisms. Margulis presented endosymbiosis as a major form of evolution by symbiogenesis.
Eukaryote: An organism whose cells contain a nucleus and other membrane-bound compartments. The cell type whose evolutionary origins Margulis’s theory sought to explain.
Ivan Wallin: An American anatomist who proposed in the 1920s that mitochondria originated from bacteria living inside other cells. His early symbiosis proposal anticipated one part of the theory Margulis later developed.
Mitochondrion: A membrane-bound organelle that produces most cellular ATP through oxidative phosphorylation in eukaryotic cells. Its bacterial ancestry is a principal claim of Margulis’s modern endosymbiotic theory.
On the Origin of Mitosing Cells: Margulis’s 1967 paper arguing that mitochondria, plastids, and other cell structures have symbiotic origins. This publication introduced the modern case that later became known as her endosymbiotic theory.
Evolutionary transition: A major change in biological organization that creates new levels or forms of individuality. The incorporation of symbionts illustrates how cooperation can produce a new cellular organization.
Konstantin Mereschkowski: A Russian botanist who argued in 1905 that chloroplasts descended from symbiotic photosynthetic organisms. His account of chloroplast origins was a historical precursor to Margulis’s argument.
Chloroplast: A photosynthetic organelle in plants and algae that converts light energy into chemical energy. Margulis argued that chloroplasts descend from photosynthetic bacteria incorporated by ancestral cells.

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