Symbiogenesis

Symbiogenesis is the merging of two separate organisms to form a single new organism. The idea originated with Konstantin Mereschkowsky in his 1926 book Symbiogenesis and the Origin of Species, which proposed that chloroplasts originate from cyanobacteria captured by a protozoan.^[1] Today both chloroplasts and mitochondria are believed to have such an origin; this is the endosymbiotic theory.

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In Acquiring Genomes: A Theory of the Origins of Species, biologist Dr. Lynn Margulis argued that symbiogenesis is a primary force in evolution. According to her theory, acquisition and accumulation of random mutations are not sufficient to explain how inherited variations occur; rather, new organelles, bodies, organs, and species arise from symbiogenesis.^[2] Whereas the classical interpretation of evolution (the modern evolutionary synthesis) emphasizes competition as the main force behind evolution, Margulis emphasizes cooperation.^[3]

Many ecologists agree, but this idea has little support from other evolutionary biologists. They see little evidence that symbiogenesis has had a major impact on eukaryotic life, or that much of its diversification can be attributed to it. Other than the two examples of mitochondria and chloroplasts, there is no clear evidence of other major traits or transitions that can be attributed to symbiogenesis.

A fundamental principle of modern evolutionary theory is that mutations arise one at a time and either spread through the population or not, depending on whether they offer an individual fitness advantage. Nevertheless, this general case may not apply to all examples of evolutionary change. Indeed, genome mapping techniques have revealed that family trees of the major taxa appear to be extensively cross-linked - possibly due to lateral gene transfer.^[4]

References

Important publications

• Konstantin Mereschkowsky. Symbiogenesis and the Origin of Species. 1926.
• Lynn Margulis. Symbiotic Planet: A New Look at Evolution. Amherst, MA: Perseus Books Group, 1998. ISBN 0-456-07271-2.
• Lynn Margulis, Dorion Sagan. Acquiring Genomes: A Theory of the Origins of Species. Amherst, MA: Perseus Books Group, 2002. ISBN 0-465-04391-7.