Symbiogenesis

Symbiogenesis is the evolutionary emergence of new biological forms or lineages through stable association and integration of previously independent organisms. It is most clearly demonstrated by the origins of mitochondria and chloroplasts from bacterial ancestors.

Endosymbiotic theory: The theory that mitochondria and chloroplasts originated as bacteria living inside ancestral eukaryotic cells. It explains the best-supported case of symbiogenesis: bacterial partners becoming organelles.
Konstantin Mereschkowski: A Russian botanist who proposed that chloroplasts originated from symbiotic bacteria. His 1905 theory proposed symbiogenesis as a source of evolutionary novelty.
Symbiosis: A close, persistent interaction between organisms of different species. Symbiogenesis is an evolutionary outcome of some long-lasting symbiotic associations.
Primary endosymbiosis: The incorporation of a bacterium directly into a eukaryotic host, giving rise to a new organelle lineage. It describes the origin of plastids from cyanobacteria in ancestral eukaryotes.
Eukaryogenesis: The evolutionary process by which the first eukaryotic cells arose. The roles and timing of symbiosis in the origin of the eukaryotic cell remain debated.
Mitochondrion: A membrane-bound organelle that generates most of a eukaryotic cell’s usable energy through respiration. Mitochondria are descendants of bacterial endosymbionts incorporated into ancestral cells.
Andrey Famintsyn: A Russian botanist who studied algae and argued that chloroplasts were independent organisms incorporated into cells. His work helped establish early scientific arguments for symbiotic organelle origins.
Natural selection: The process by which heritable traits that improve reproductive success become more common in populations. Selection can favor stable partnerships and traits that make their integration beneficial.
Secondary endosymbiosis: The incorporation of a eukaryotic alga by another eukaryote, transferring its plastid to the host lineage. It shows how symbiotic integration can recur after the original bacterial-to-eukaryote event.
Asgard archaea: A group of archaea whose genomes contain genes resembling those found in eukaryotes. Their discovery has sharpened debate over the host lineage involved in eukaryote origins.

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LichenRelated: Lichen partnerships raise questions about how repeated association can shape organismal identity.