Microbial Microcosm

The missing piece in our understanding of evolution may be the importance of symbiosis in the development of new forms of life

One of the articles in Exploring Our Interconnectedness (IC#34)
Originally published in Winter 1993 on page 18
Copyright (c)1993, 1996 by Context Institute

Just how interconnected are we? The work of biologist Lynn Margulis and writer Dorion Sagan indicates we’re interconnected in ways few of us have probably ever considered. In fact, instead of viewing ourselves as the pinnacle of evolution, it may be more accurate to think of ourselves as a colony of closely associated bacteria.

Carla Cole based the following on the work of Lynn Margulis and Dorion Sagan, including an article of theirs, The Parts: Power to the Protoctists, which appeared in the September/October 1992 issue of Earthwatch. (See the sidebar for more information on their work.)

All life on Earth today derived from common ancestors. The first to evolve – yet the last to be studied in detail – are bacteria. Scientists have now discovered that bacteria not only are the building blocks of life, but also occupy and are indispensable to every other living being on Earth. Without them, life’s essential processes would quickly grind to a halt, and Earth would be as barren as Venus and Mars.

Far from leaving microorganisms behind on an evolutionary ladder, we more complex creatures are both surrounded by them and composed of them. New knowledge of biology alters our view of evolution as a chronic, bloody competition among individuals and species. Life did not take over the globe by combat, but by networking. Life forms multiplied and grew more complex by co-opting others, not just by killing them.

In the first two billion years of life on Earth, bacteria – the only inhabitants – continuously transformed the planet’s surface and atmosphere and invented all life’s essential, miniaturized chemical systems. Their ancient biotechnology led to fermentation, photosynthesis, oxygen breathing, and the fixation of atmospheric nitrogen into proteins. It also led to worldwide crises of bacterial population expansion, starvation, and pollution – long before the dawn of larger forms of life.

Bacteria survived these crises because of special abilities that other life forms lack and that add whole new dimensions to the dynamics of evolution. First, bacteria routinely transfer their genes to bacteria very different from themselves. The receiving bacterium can use the visiting, accessory DNA (the cell’s genetic material) to perform functions that its own genes cannot mandate. Bacteria can exchange genes quickly and reversibly. Unlike other life forms, all the world’s bacteria have access to a single gene pool and hence to the chemical prowess of the entire bacterial kingdom.

This extreme genetic fluidity makes the very concept of species of bacteria meaningless. The result is a planet made fertile and inhabitable for larger life forms by a worldwide system of communicating, gene-exchanging bacteria.

Bacteria also have a remarkable capacity to combine their bodies with other organisms, forming alliances that may become permanent. Fully 10 percent of our own dry weight consists of bacteria, some of which – like those in our intestines that produce vitamin B12 – we cannot live without.

Mitochondria live inside our cells but reproduce at different times with different methods from the rest of our bodies’ cells. They are descendants of ancient bacteria. Either engulfed as prey or invading as predators, these bacteria took up residence inside foreign cells, forming an uneasy alliance that provided waste disposal and oxygen-derived energy in return for food and shelter. Without mitochondria, the nucleated plant or animal cell cannot breathe and therefore dies.

This symbiogenesis, the merging of organisms into new collectives, is a major source of evolutionary change on Earth. The results of these first mergers were protoctists, our most recent, most important – and most ignored – microbial ancestors. Protoctists invented our kind of digestion, movement, and our tactile and visual systems. They came up with speciation, cannibalism, genes organized on chromosomes, and the ability to make hard parts (like teeth and skeletons). These complex microscopic beings and their descendants even developed the first genders and our kind of cell-fusing sexuality involving penetration of an egg by a sperm.

Discovering the microcosm within and about us changes – indeed, reverses – the way we look at living things and picture their evolution on the planet. For instance, since all life on Earth evolved from bacteria, it makes more sense now to think of beetles, rose bushes, and baboons as communities of former bacteria and protoctists than as higher animals or plants.

The traditional belief in "man, the highest animal" endures because the shift to a more egalitarian view of the world that respects and empowers all life is an enormous step.

Acknowledging that our ancestors are bacteria is humbling and has disturbing implications. Besides impugning human sovereignty over the rest of nature, it challenges our ideas of individuality, uniqueness, and independence. It even violates our view of ourselves as discrete physical beings separated from the rest of nature and – still more unsettling – it challenges the alleged uniqueness of human intelligent consciousness.

Those who speak only for the special interests of human beings fail to see how interdependent life on Earth really is. Without the microbial life forms, we would sink in feces and choke on the carbon dioxide we exhale. We cannot view evolutionary history in a balanced manner if we think of it only as a four-billion-year preparation for "higher" organisms, like humans. Most of life’s history has been microbial. We are recombinations of the metabolic processes of bacteria that appeared before, during, and after the accumulation of atmospheric oxygen some 2,000 million years ago.

The ancient, vast, and fundamental nature of our interdependence with other forms of life may be humbling, but it provides a basis for facing the future free of crippling delusions. Despite all our conceits, we are as much exploited as exploiters, as much consumed as consumers. The lesson of evolutionary history is that it will be through conservation, interaction, and networking, not domination, that we avert a premature end to our species.


Lynn Margulis and Dorion Sagan, whose work inspired and informed this article, have written extensively on biological interconnectedness.

Microcosmos: Four Billion Years of Evolution From Our Microbial Ancestors, explores in delightful but scientifically rigorous prose the issues raised in this article. The book is now available in paperback from Touchstone Press.

Lynn and Dorion also wrote Mystery Dance: On the Evolution of Human Sexuality (Simon and Schuster, NY, 1991), The Garden of Microbial Delights (second edition, Kendall-Hunt, 1993), and The Microcosmos Coloring Book. Lynn authored Symbiosis in Cell Evolution (second edition, WH Freeman, NY, 1993) and coauthored, with K.V. Schwartz, Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth (second edition, WH Freeman, NY, 1988).

Lynn is distinguished university professor in the biology department at the University of Massachusetts at Amherst. She was elected to the National Academy of Sciences in 1983.

She is best known for developing the theory, now widely accepted, that cells with nuclei evolved from the merger of two or more different types of bacterial cells.

She also provided some of the biological underpinnings for the development of James E. Lovelock’s Gaia hypothesis. Lynn is now working on the controversial theory that sperm tails in humans and other animals evolved from bacteria known as spirochetes.

Dorion Sagan, author of Biosheres: Metamorphosis of Planet Earth (Bantam, paperback; McGraw Hill, NY, 1990, hardcover) and sleight-of-hand magician, lives in Northampton, MA, where he is working on his second novel.