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Evolution's Other Narrative

Why science would benefit from a symbiosis-driven history of speciation.

Bradford Harris

The Story of Symbiogenesis

2013-11MacroHarrisF2.jpgClick to Enlarge ImageThroughout the first half of the 20th century in Western Europe and America, even as scientists reduced their investigations on evolution down to the microscopic level of the cell, the individualist school of thought continued to dominate. Researchers assumed that the genes inside the cell nucleus contained all the information determining an individual’s functions, traits, and health, and therefore the individual’s evolutionary prospects. The new preoccupation with genetic competition only extended the appeal of interpreting evolution as survival of the fittest. Nonetheless, struggling against this reinforced structure, a minority of investigators maintained interest in symbiotic interpretations of biological adaptation. For these scientists, nuclear genetics told only part of the evolutionary story.

One of the most important of these symbiotic thinkers was Ivan Wallin of the University of Colorado, Boulder. During the 1920s he set out to investigate the history of the eukaryotic cell organelles called mitochondria—the globular structures outside the nucleus that produce the cell’s energy. Wallin proposed a radical hypothesis: Mitochondria did not evolve endogenously through a long history of random nuclear genetic mutation; instead, mitochondrial organelles inside our cells descended from bacteria that had formed cooperative associations with our cells—with us. This idea contradicted combative survival of the fittest.

In 1927 Wallin published Symbionticism and the Origin of Species, in which he pointed out that mitochondria’s possession of their own, distinct genes showed their independent bacterial ancestry. This was the first direct genetic evidence presented to the western European and American scientific community that supported the theory of symbiogenetic evolution.

Wallin should have caused a sensation, but Western scientists failed to take note. Symbiogenetic insights remained overshadowed by the preoccupation with cell nuclei. Especially after the resurrection of Gregor Mendel’s work, most scientists believed that any genetic material that might be found outside the cell nucleus was unimportant to evolution.

The public, meanwhile, was less interested in esoteric variations in evolutionary theory among experts than they were with the creationism-evolution debate during the 1925 State of Tennessee v. Scopes trial. Whether evolution was real—not how it proceeded—was the popular drama. When Scopes was a fading memory in the 1950s, James Watson’s and Francis Crick’s revelation of the double-helical structure of DNA subsumed symbiogenesis under a whole new generation of enthusiasm for nuclear genetics. Yet another generation passed before the evolutionary biologist Lynn Margulis succeeded in revivifying the insights of Wallin and the earlier Russian symbiogeneticists.

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