In Pursuit of Life's Beginnings

Search fro the Universal Ancestors: The Origins of Life. H. Hartman, J.G. Lawless and R Momson, eds. Blackwell Scientific Publications, Boston, 1987. 142 pp. $14.95 PB. The purpose of this excellent book, originally prepared as a NASA report, is twofold. First, it is to summarize the major converging lines of experimental inquiry into the earliest phases of the evolution of life on Earth. Second, it is to look ahead, with recommendations for future research. With 27 contributors, including several in the prima donna class, it is a wonder that the editors managed to maintain such a consistent tone of voice, avoiding on the one hand a circus of hobby horses and, on the other, a bland affirmation of received doctrine. Instead, it is a model of balance, with difficulties carefully pointed out. I hope that the readers of this book will include textbook writers, television producers and others who so often feel obliged to explain in a sentence or two how life must have started from proto-organisms feeding on an ocean of biochemicals generated in a methane-dominated atmosphere by thunderstorms and ultraviolet light. Well, maybe, but this is not the only model or even the preferred one. The best geochemical evidence now puts carbon dioxide and nitrogen as the major early atmospheric constituents, and it is not at all clear that such an atmosphere would have provided a good source of amino acids, etc. There are several other possible sources of the reducing power needed to make organic molecules. One important possibility, backed by experiment (but calling for more) is ferrous iron derived from the mantle. Neither is it clear that the first organisms were just simpler versions of today's organisms. The idea that earlier biochemical materials might have included clay minerals, so that early biochemistry was more like present-day geochemistry, is at least as sensible as the more generally held opposite notion—preferred here—that early geochemistry ran in part along modern biochemical lines. Each of these possibilities is considered, however, as is the notion that the truth may lie in between. In any case it was a long way from the first reproducing mutating systems in our ancestry to the Universal Ancestors of the title. The term "Universal Ancestor(s)" by the way, is not in the index and appears only once in the book. What is being referred to is not the first system(s) able to evolve through natural selection but rather some organism, or population of organisms, ancestral to all forms of life now on Earth. Indeed there is good evidence for such beings, which are better described as Last Common Ancestors. And it is significant that we can infer that they already contained the code-dependent nucleic acid-protein system with which we are familiar. But as such they were winners not beginners. Special creation or gigantic chance apart, there must have been an earlier darker phase of evolution through natural selection that brought such exquisite engineering into existence. It is the nature of this phase that constitutes the core of the problem of the origin of life. The book asks: "What is the simplest chemical system that is capable of complete genetic self-replication and open-ended Darwinian evolution?" It is a good question. It is reasonable to suppose that there were such systems on the primitive Earth, simple enough to have arisen without prior Darwinian evolution, and that we should be able to recreate something of their kind in the laboratory—and watch them evolve. The news is good for young researchers in this field there is plenty to do, and the Big Experiment lies ahead. Cairns-Smith is a reader in chemistry at the University of Glasgow, G12 8QQ, UK He is the author of Seven Clues to the Origin of Life (Cambridge University Press, 1986).

In Pursuit of Life's Beginnings

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