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Endosymbiotic theory

1967MajorContested

Lynn Margulis argues that mitochondria and chloroplasts began as free-living bacteria engulfed by other cells. DNA evidence later confirms it.

Contested history

Consensus: Mitochondria and chloroplasts descend from bacteria taken into ancestral cells.

Endosymbiotic origin of mitochondria and plastidsEstablished
Their own DNA, ribosomes and double membranes group them with alphaproteobacteria and cyanobacteria.
Spirochete origin of cilia and flagellaUnsupported
Margulis proposed it, but cilia lack their own genome and no bacterial ancestor has been found.

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