The endosymbiotic theory argues that mitochondria, plastids (e.g. chloroplasts), and possibly other organelles of eukaryotic cells, originate through symbiosis between multiple microorganisms. According to this theory, certain organelles originated as free-living bacteria that were taken inside another cell as endosymbionts. Mitochondria developed from proteobacteria (in particular, Rickettsiales, the SAR11 clade, or close relatives) and chloroplasts from cyanobacteria.
Read more about Endosymbiotic Theory: History, From Endosymbionts To Organelles, Evidence, Secondary Endosymbiosis, Extensions
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“It is not enough for theory to describe and analyse, it must itself be an event in the universe it describes. In order to do this theory must partake of and become the acceleration of this logic. It must tear itself from all referents and take pride only in the future. Theory must operate on time at the cost of a deliberate distortion of present reality.”
—Jean Baudrillard (b. 1929)