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Earth mother, microbe lover

Biologists agree that more life is produced on earth than can possibly survive; that natural selection is the process by which some small fraction of what is produced survives; and that species both stay the same (ie inherit characteristics) through successive generations, and also change, sometimes giving rise to new species.

Biologists differ, however, on how these processes work, and especially on how evolutionary innovation - the production of new species - arises.

Lynn Margulis says: "Some smart Englishmen in the early part of this century recognised that Mendel had a very good set of rules for the stability of change through generations; those are called the rules of genetics. They also realised that Darwin had a very good explanation of the change in organisms through time. So they developed an imaginative scheme called neo-Darwinism to connect Mendel's stability with Darwin's change and they made up an incredible superstructure and attributed the sources of variation to what they called heritable mutations, ie random mutations in the genes heritable in the next generation."

In radical disagreement, Margulis attributes the main source of evolutionary change to symbiosis. "I believe that neo-Darwinism is a kind of 20th-century aberration and that it will disappear just as plasmogenesis, phlogiston theory and many other ideas in science have disappeared."