Microcosmos: Four Billion Years of Evolution From Our Microbial Ancestors by Lynn Margulis and Dorion Sagan (Summit: $17.95)
The story of life on Earth is usually told like this:
First there was the primordial soup, which sloshed around for a while getting zapped by lightning and whatnot, creating amino acids, the building blocks of proteins. These proteins eventually got together as DNA, which in turn formed cells.
Then the cells got together as multicelled organisms, and eventually one or more of them crawled out of the oceans onto the land. And that's when the story got interesting because it leads inexorably to the vertebrates and the apes and people, who, after all, figured all this out.
This scenario, while accurate as far as we know, suffers from a certain parochialism. It is like telling world history as the story of Egypt, Greece, Rome, Europe and the United States--without reference to anything else. It says, "Here we are, and the whole history of the world and of life leads to us." Just so.
Lynn Margulis, a distinguished biologist, and Dorion Sagan, a first-rate science writer who is also Margulis' son, say that in the usual telling of evolution, the emphasis is misplaced. The important stuff, they say, happened at the beginning, during those billions of years of amino acids and single-celled organisms that are usually ignored or passed over in a trice.
That period accounts for 80% of the time that living things have been on Earth. By the time the first multicelled organism crawled out of the ocean, all of the processes of life that still rule the planet had been set, Margulis and Sagan say.
The goal of "Microcosmos" is to right this oversight. Indeed, human beings don't appear until the last third of the book. Until then, we are treated to a fascinating, engrossing, superbly written account of how the conditions of the primitive Earth affected and were affected by the mechanisms of evolving forms of life and how those solutions remain with us today.
According to the authors, the most important and far-reaching of these mechanisms is cooperation. Margulis and Sagan argue that the driving force of evolution was not a competition among species from which the fittest survived. Rather, they say, what kept life going and still keeps life going is symbiosis--cooperation.
Invasion of Bacteria
Evolution really got going, they think, when bacteria invaded cells and began living inside them. The evidence for that, they say, is in every cell on Earth today that contains a nucleus. Their central argument is that the various vital structures found in all nucleated cells are remnants of early bacteria that merged with existing cells early in life's history, mergers that benefited both the cells and the bacteria.
"All the familiar creatures of the earth today," the authors write, "are composites of nucleated cells. The nucleated cells themselves are the result of prokaryotic (early life) mergers. And each cell with a nucleus is packed with the deep-breathing mitochondria that once upon a time were bacteria."
Similarly, they say, other bacteria merged with early cells to form additional structures vital to life as we know it. The authors claim that the ability of our brains to process information, which is probably our species' most distinguishing characteristic, comes from the merger of spirochetes--bacteria--with those early cells.
"Once, microscopic spirochetes had to swim furiously for their lives," they say. "Now, millions of years later, packed into an organ called the brain, their nucleotide and protein remnants conceive and direct the actions of a highly complex amalgam of evolved bacterial associations called a human being."
Little More Than Guesses
If all this sounds more than a bit speculative, you are right. One of the reasons that so little attention is usually paid to those first several billion years of life is that so little is known about them. Understandably, there isn't much evidence around, though archeobiologists have learned a great deal in recent years. Still, inference is the most important analytical tool they have, and their theories are little more than guesses.
This book's weakness is that it does not distinguish clearly between what is known and what the authors are filling in. They have put it all together in a virtually seamless web that makes most of their speculations sound like fact.
For most of the book, this is merely annoying. In the last chapter, however, the authors abandon the past and talk about where evolution will take us in the future. In the process, they go off the deep end completely, but you wouldn't know it by the tone.