Basic Books, 1999
Reviewed by Michael Colebrook
(for the original, Weidenfeld & Nicolson, 1998 version)
Lynn Margulis has played a leading role in a fundamental transformation in our views about the early history of life on this planet. It is perhaps significant that she was, for a time, married to Carl Sagan. Most of The Symbiotic Planet is an account of a personal odyssey to gain acceptance for her theory that symbiosis, the term used to describe the phenomenon of organisms living together to their mutual advantage, has played a major role in biological evolution. This represents a significant shift from classical neo- Darwinism which sees competition as the virtually the only selection mechanism.
In particular, Lynn Margulis has argued that the emergence of the eukaryotic cell, the complex cell containing a nucleus, that is the basic building block of all animals, plants and a host of single celled organisms, is the result of the fusion of pre-existing bacterial cells.
The cell nucleus (containing most of the genetic material), the mitochondrion (energy producing centre) and in green organisms, the chloroplast (containing the chlorophyll) are now generally accepted as having their origins as free-living bacteria which, long ago, were partially eaten and trapped inside the bodies of other bacteria. What started out as predation finished up as co-operation as the trapped bacteria continued to function inside the bodies of their hosts. This process sorted itself out by new divisions of labour within the new complex cells.
The process of evolution by symbiosis is a strange and fascinating story. Even stranger is the idea that sexual reproduction started out as cannibalism (there may be some who say it still is!). The book goes on to describe briefly some of the other significant examples of symbiosis. For example, it is probable that the lichens, which are symbiotic couplings between algae and fungi, were among the first large organisms to survive on dry land.
In the final chapter, Lynn Margulis looks at Gaia, the concept of the earth as a form of super- organism. She argues that Gaia, as far as material substances are concerned, is a closed system. This being so then it can only maintain itself by reusing the same materials over and over again and this is essentially a cooperative process.
All this has implications for how humans behave towards the natural world and it is worth quoting the final paragraph of the book. “We cannot put an end to nature; we can only pose a threat to ourselves. The notion that we can destroy all life .. is ludicrous. I hear our nonhuman brethren snickering: ‘Got along without you before I met you, gonna get along without you now’.. The tropical forest trees are humming to themselves, waiting for us to finish our arrogant logging so they can get back to their business of growth as usual. And they will continue their cacophanies and harmonies long after we are gone.”