A trilobite of one's own

LIFE: AN UNAUTHORISED BIOGRAPHY; A Natural History of the First 4,000,000,000 Years of Life on Earth by Richard Fortey, HarperCollins pounds

The "Unauthorised" tag usually indicates that a biography has an ambivalent attitude to its subject, and hints at dramatic revelations. There will be no joy, however, for anybody leafing through Richard Fortey's pages in search of salacious titbits from the primordial soup, or for what the government doesn't want you to know about the extinction of the dinosaurs. Nor is he a whimsical writer, as the arch title might suggest, though he is warm and amusing. But then Georges Perec's title Life: A User's Manual didn't set the tone for the book it fronted either.

Fortey's attitude to his primary subject - the entire history of life on this planet - is properly respectful. He rejects, for example, the fondness of popular science for the "domestication" of time, in the common metaphorical device of the clock face, trivialising what should be regarded with awe. Rather than comparing the human tenancy of the planet to the last minute before midnight, he likens it to the size of a pebble on the Arctic shore he combed as a young researcher for fossils. The distance he could throw the pebble represents the distance to the age of dinosaurs. Beyond that point lie more beaches, mist, jetsam, and eventually the sea. As he says, this conveys a "vaguer but truer" sense of time.

The colour of the book comes from his love for his secondary subject, the construction of what we know about life on Earth. The "unauthorised" label acknowledges that there will never be an official, definitive version. Since prehistory attempts to tell so much longer a story than history, but with so much less to go on, it is much more liable to revisions, disputes and abrupt changes of direction. A new fossil find or a clever new dating technique can turn a whole domain of knowledge upside down overnight. As a palaeontologist at the Natural History Museum, whose curators endorsed the Piltdown fakes as genuine, Fortey cannot but be mindful of where undue certainty can get a scientist.

His response to the plasticity of prehistory is to emphasise the personal nature of his narrative. The introductory tale of his Arctic expedition is even more memorable for its human figures than for its landscape studded with fossils. Fortey and his senior colleague had little in common beyond a tent and their undergraduate status, but they achieved a relationship of "working cordiality". Then their exam results arrived. Fortey got a first at the end of his second year; his companion, who had expected to go on to a PhD, got a lower second in his finals. With exquisite timing, a pack of ice floes then sealed them in for several weeks.

Characteristically, Fortey describes this awkward reversal of fortunes in terms of luck. Orthodox Darwinists would be more inclined to see it as evidence of his greater fitness. But for him, as for Stephen Jay Gould, one of the chief morals of life's story is that it's often a lottery. The survival of many individuals, and species, is the consequence of luck rather than adaptation. He disagrees with Gould, however, over the significance of the Burgess Shale fossils, which Gould discusses in his book Wonderful Life. Fortey argues that these specimens are not so radically different from familiar classes of organism as Gould contends.

Unlike other critics of Gould, though, he is calm and amicable. He is similarly benign about the entire human species when he skates over the evidence that our hunter-gatherer ancestors drove many species of large animals to extinction (a case Colin Tudge builds implacably in The Day Before Yesterday). These are not relentless pursuits of hypotheses through ancient landscapes. They are, rather - to borrow the title of Gould's essay series - reflections in natural history.

Naturally, they reflect his own dispositions. There is more detail on trilobites, his research specialism, than on trees. Our own lineage gets more space than it would merit on the basis of the time it has been in existence. But this is a biography, not an encyclopedia or a textbook. It encourages the reader to participate in its author's reflections, not to sit at his feet and imbibe wisdom.

Not the least of its charms is Fortey's taste for the smaller pleasures of natural history. One of these is the privilege of naming species that is the discoverer's reward. Almost bashfully, he notes the existence of a "rather insignificant" trilobite called Forteyops. How much sweeter must have been the joy of the mollusc specialist when a new member of the genus Abra appeared, allowing him to fulfil his ambition of proposing the species name cadabra. And sometimes names are apter than they first appear. Hallucigenia, one of the bizarre fauna of the Burgess Shale, turned out to have been drawn the wrong way up.