Tuesday, March 15, 2011

Dr. Lynn Margulis: Symbiotic evolution

Third Culture excerpt

Symbiosis is a physical association between organisms, the living together of organisms of different species in the same place at the same time. My work in symbiosis comes out of cytoplasmic genetic systems. We were all taught that the genes were in the nucleus and that the nucleus is the central control of the cell. Early in my study of genetics, I became aware that other genetic systems with different inheritance patterns exist. From the beginning, I was curious about these unruly genes that weren't in the nucleus. The most famous of them was a cytoplasmic gene called "killer," which, in the protist Paramecium aurelia, followed certain rules of inheritance. The killer gene, after twenty years of intense work and shifting paradigmatic ideas, turns out to be in a virus inside a symbiotic bacterium. Nearly all extranuclear genes are derived from bacteria or other sorts of microbes. In the search for what genes outside the nucleus really are, I became more and more aware that they're cohabiting entities, live beings. Live small cells reside inside the larger cells. Understanding that led me and others to study modern symbioses.

Symbiosis has nothing to do with cost or benefit. The benefit/cost people have perverted the science with invidious economic analogies. The contention is not over modern symbioses, simply the living together of unlike organisms, but over whether "symbiogenesis" — long-term symbioses that lead to new forms of life — has occurred and is still occurring. The importance of symbiogenesis as a major source of evolutionary change is what is debated. I contend that symbiogenesis is the result of long-term living together — staying together, especially involving microbes- -and that it's the major evolutionary innovator in all lineages of larger nonbacterial organisms.


  1. I just read this in Discover magazine in this month's issue.

    Supposedly this idea is widely accepted in Russia. She makes some very good points against natural selection. I think the theory sounds very good and makes a lot of sense.

  2. That is not to say natural selection does not have a place in the theory of evolution, according to her, but it is incomplete. She says that evolution is the selector while symbiogenesis is the innovator.


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