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In the last blog, I questioned the creative role of natural selection in evolutionary innovation. To clarify further what I had in mind, this blog will look at one of the truly creative processes of tremendous importance in evolutionary history: symbiotic mergers of two distinct organisms to generate a third new one (symbiogenesis). Without symbiogenetic mergers, we would not exist.

The classic example of symbiogenesis is the formation of lichens, the moss-like forms that live on rock surfaces. Lichens arise from a merger of a fungus and a photosynthetic microbe, either a cyanobacteria or (more commonly) an alga. The resulting lichen has both the fungus’ ability to grow by spreading adherent filaments over the rocks and the photosynthetic capacity to produce food from sunlight and carbon dioxide in the atmosphere.

Lichens were considered a separate group of organisms until 1867, when Swiss botanist Simon Schwendener proposed they were a symbiotic association. It had to wait until 1939 for Eugen Thomas to artificially synthesize a lichen in the laboratory.

The great proponent of symbiogenesis as a major force in evolution was Lynn Margulis, who suddenly passed away late last year. She and her son, Dorion Sagan, summarized her ideas in the 2003 book, Acquiring Genomes: The Theory of the Origins of the Species.

Lynn was most widely known since the 1970s for championing ideas that organelles within nucleated eukaryotic cells are descended from endosymbiotic bacteria (Margulis, Origin of Eukaryotic Cells, 1970). Lynn’s position was vindicated when the methods of molecular taxanomy and phylogeny, pioneered by Carl Woese at the University of Illinois (Woese 1981), made it possible to demonstrate that the oxidative energy-producing organelle of eukaryotic cells, the mitochondrion, actually descended from a specific type of bacterium.

Since all eukaryotic cells have mitochondria (or a degenerate form of this organelle), the ancestral eukaryotic cell must have had one too. Thus, the origin of the nucleated eukaryotic cell from prokaryotic (pre-nucleus) precursors involved at least one symbiogenetic event to acquire the mitochondrion...

Cell Mergers and the Evolution of New Life Forms: Symbiogenesis Rather Than Selection | The Huffington Post

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