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No. 51: May-Jun 1987

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Evolution Through Mergers

The overview in Natural History describes how, in theory, the mitochondria in cells were created by bacterial invasion. The presence of chloroplasts in plants, too, may have come about in this way. A case also exists for the alliance of spirochetes with cells to form flagella and cilia. These three "mergers" provided cells with metabolism, photosynthesis, and mobility. Margulis and Sagan obviously do not believe that the "bacterial connection" ended there. They bring their article to a close with an almost poetic manifesto that we now quote in part. The context of the quotation is their assertion that plant and animal evolution would never have taken place unless one life form attacked another and the latter defended itself, all this followed by accomodation and the development of a symbiotic relationship.

"Uneasy alliances are at the core of our very many different beings. Individuality, independence -- these are illusions. We live on a flowing pointillist landscape where each dot of paint is also alive. Earth itself is a living habitat, a merger of organisms that have come together, forming new emergent organisms, entirely new kinds of 'individuals' such as green hydras and luminous fish. Without a a life-support system none of us can survive. It is in this light that we are beginning to see the biosphere not only as a continual struggle favoring the most vicious organism but also as an endliess dance of diversifying life forms, where partners triumph."
(Sagan, Dorion, and Margulis, Lynn; "Bacterial Bedfellows," Natural History, 96:26, March 1987.)

Comment. One should observe that there is a strong connection between the Gaia concept of a living planet and the theory of symbiotic evolution. Strong philosophical statements are also inherent in this outlook on life and its development. For example, individuality and free will would seem to be denied. Also, can life forms be "vicious" and yet "cooperative" at the same time?

From Science Frontiers #51, MAY-JUN 1987. 1987-2000 William R. Corliss