by Lynn Margulis and Dorian Sagan

This piece was originally published in Home! A Bioregional Reader, edited by Van Andruss, Christopher Plant, Judith Plant, and Eleanor Wright, New Society Publishers, copyright 1990.

The symbiotic process goes on unceasingly. We organisms of the macrocosm continue to interact with and depend upon the microcosm, as well as upon each other. Certain families of plants (such as the pea family, including peas, beans, and relatives such as clover and vetch) cannot live in nitrogen-poor soil without the nitrogen that comes from such plants. Neither cows nor termites can digest the cellulose of grass and wood without communities of microbes in their guts. Fully ten percent of our own dry body weight consists of bacteria, some of which, although they are not a congenital part of our bodies, we can’t live without. No mere quirk of nature, such co-existence is the stuff of evolution itself.

Excerpted from Microcosmos: Four Billion Years of Microbial Evolution, New York: Summit Books, 1986.

Lynn Margulis (1938-2011) was a biologist and writer whose work dramatically transformed the modern understanding of of the importance of symbiosis in evolution and the evolution of cells with nuclei. She received the National Medal of Science from President Bill Clinton in 1999.

Dorian Sagan (b. 1959) is a writer and the son of Lynn Margulis and Carl Sagan. His many publishing credits include a number of books co-written with his mother, as well as a biography of her.

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