Microcosmos: Four Billion Years of Microbial Evolution [Paperback]

After some preliminary discussion of how life started, the authors move into the realm of cellular organisms. The various ideas of life's origins are fascinating, but not until it achieved the level of individual micro-organisms does life take on meaning. The authors describe the events occurring during the long reign of the prokaryotes. These simple organisms were little more than a bag containing some genetic information. Yet, their emergence was the start of true life. While it's easy to think this "primitive" organism has faded into oblivion with the passage of time, the authors remind us that all our bacterial neighbours [and some inhabiting us!] are of that distant family.

When conditions varied in certain localities, these simple creatures performed some amazing tricks. One of these resulted in a devastating event the authors term The Oxygen Holocaust. The original prokaryotes thrived on hydrogen, making useful compounds of it and other elements. Since the best available source was water, the resultant waste product was oxygen. As this pollutant entered the atmosphere many organisms were forced to change their lifestyle or die out. The massive changes resulting increased the complexity of many organisms that began adding new protective devices to their structures. According to the authors, some cells had already initiated a new survival technique - the merging of various prokaryotic cells resulting in a new type. The new cell packaged its genetic material in a nucleus, creating the form known as the eukaryotes. Eukaryotic cell structure led down the long evolutionary track to complex creatures like ourselves.

There is a goal behind their descriptions of life's evolution. They remind us that textbook illustrations of individual bacteria are misleading. All Bacteria "clump" in some form or another as part of their survival strategy. Because these tiny organisms encounter so many environments and because their genetic makeup allows astonishing variation, many bacteria form communities with various groups performing specific tasks. These roles may include shielding the rest of the community from environmental hazards, processing food and waste or mobility. This revelation also points up a major theme of this book - cooperation has played a greater role in evolution than has competition. Cooperation is a survival strategy whereas competition may leave too few winners to ensure perpetuation of the species. How far can the cooperation extend in a planet of highly varying environments?

That question is answered in their concluding chapter. In it, they extend their previous narrative to reinforce the case for James Lovelock's Gaia thesis. In their view, Gaia is a "superorganism" extending throughout the entire biosphere. It is self correcting and self-regulating - indeed, the role of evolution is but the "operating system" of this global organism. Since the oxygen we breathe came from waste-expelling microbes, more than lifeforms are contained within Gaia. The atmosphere and oceans aren't habitats and support systems for life, but an integral part of a grander structure, one thoroughly integrated. One can only wonder what Darwin might have thought of this extrapolation of his idea of evolution by natural selection. This is not the place to debate Lovelock's thesis. While Gaia has been strenuously challenged by other commentators, Margulis and Sagan weave a tightly knit support for the idea. They do it earnestly and with clarity, and their view should be given some consideration. Strangely, however, while they have no qualms about describing certain theories about life's evolutionary progress as "still a mystery" or "controversial," this aspect of the book is presented as a given. The inconsistency is glaring, but shouldn't detract from the worth of the book as a whole. [stephen a. haines - Ottawa, Canada]