John Maynard Smith and Eors Szathmary

THE ORIGINS OF LIFE

From the birth of life to the origins of language

This book is described as a more popular version of the authors' earlier work, The Major Transitions in Evolution (W.H.Freeman, Oxford and New York), published in 1995. I am not sure that the decision to make this abridgement (which is what in fact it is) was entirely wise, since the new book sacrifices a good deal of information in the original without, in my view, a corresponding increase in easy comprehensibility.

The idea underlying both these books is that evolution depends on information passed between generations, and that there have been a number of major transitions in the way in which this has occurred. The authors set out to explain these transitions in Darwinian terms. The transitions they identify are (1) from replicating molecules to protocells; (2) from independent replicators to chromosomes; (3) from RNA as gene and enzyme to DNA genes and protein enzymes; (4) from bacterial cells (prokaryotes) to cells with nuclei and organelles (eukaryotes); (5) from non-sexual to sexual reproduction; (6) from single-celled to multi-celled organisms (animals, plants, fungi); (7) from solitary individuals to colonies with non-reproductive castes (termites, ants, bees); and (8) from primate to human societies, a step that depended on the acquisition of language. This is quite a lot to cram into less than 200 pages and inevitably corners have to be cut pretty ruthlessly. Many interesting ideas that were treated in some detail in The Major Transitions are merely touched on here or are omitted altogether (for example, Cairns-Smith's theory that primordial genes were made of clay rather than RNA). And I was particularly sorry to find that the new book omits the intriguing notion, first proposed by Geoffroy St Hilaire in the early nineteenth century, that vertebrates, with their dorsal nerve cords and ventral hearts, are upside-down descendants of annelid ancestors. Much derided at the time, this theory now receives support from the discovery of homology between genes determining dorsal structures in annelids and arthropods and genes determining ventral structures in vertebrates. The mental picture of ourselves as upside-down earthworms is surely irresistible.

There are some gains, however. One topic which is better treated in the new book than in the previous one is the question of why sex exists. It must have advantages, otherwise it would not exist, but there is little agreement among biologists about what these advantages are. It may benefit populations, it may benefit individuals, or it may benefit particular genes at the expense of others within an individual. There is some evidence for all of these possibilities. Group selection, the authors suppose, may partly explain the persistence of sexual reproduction but not its origin, which requires short-term advantage for individuals. At the individual level, sex may facilitate repair of damaged DNA. The authors say nothing about another widely held theory of sex: that it may assist in protecting individuals against parasites (see The Red Queen by Mark Ridley).

Perhaps it was over-ambitious to include a discussion of the origins of human society and of language in a book that is primarily about biology. At any rate, the treatment of these topics is pretty sketchy, and it would not be easy for a reader to follow up the ideas in more detail. For example, Steven Mithen's book The Prehistory of the Mind is alluded to but the full reference is not given. Indeed, there is no proper bibliography at all, but just a short "Further Reading" list (in which Mithen is not mentioned). Similarly, the origin of language is tied pretty firmly to Chomsky's theory of an innate "language organ", yet important and plausible alternatives do exist but are not mentioned; for example, Terrence Deacon's suggestion in The Symbolic Species that languages themselves have "evolved" to be easily learned by young children.

I found this book rather disappointing, even though it does contain interesting and important ideas. It is professedly aimed at a general readership, but I think that even readers who are not professional biologists would be better off going back to The Major Transitions. While that book admittedly contained some technical sections, these could be skipped if necessary and many of the chapters included a useful summary at the end which could be used to gain an overall impression of the authors' conclusions.