Colin Renfrew finds clear directions for navigating a complex new discipline.
It is only 15 years since the discovery that the story of the descent of man can best be investigated through the study of DNA taken from the living. This still rather astonishing breakthrough is revolutionising our understanding of our history.
Of course, archaeological finds such as stone tools and fossil remains are indispensable in completing the picture, and they form a geographical anchor for molecular-genetic research. Moreover, the study of ancient DNA extracted from the surviving bones and teeth of these ancestral humans and of their not-quite-human cousins has become increasingly important. But the greatest strides have come from the study of the genetic material of living humans, or, as Steve Olson puts it, "discovering the past through our genes".
Mapping Human History is one of the first books to tell this story in an intelligible way for the lay-reader. Notable among its predecessors but written before some of the more recent discoveries was The Great Human Diasporas by Luca and Francesco Cavalli-Sforza (1995).
Olson succeeds in making the science intelligible, and in the first chapter summarises effectively both the way DNA studies work and the clear indication that they now offer for the African origins of our species. He tells the story of the first studies using mitochondrial DNA, whose genetic information is passed exclusively through the female line, and outlines the arguments leading to the notion of the "mitochondrial mother" or "African Eve". Early in the book Olson emphasises the genetic unity of modern humans, and an important theme throughout is that contemporary genetic research consistently diminishes the significance of "race" as an indicator of human behaviour or potential. He is thorough in his treatment of the continuing prejudices over ethnicity and descent, choosing contemporary France as an example, and closes the book with a chapter titled "The end of race".
Olson achieves a global coverage. Successive parts, consisting of two or three chapters each, deal with Africa, the Middle East, Asia and Australia, Europe and the Americas. One chapter, "Sprung from a common source: genes and languages", rather boldly addresses the topic of linguistic diversity - to which molecular genetic researchers have not yet contributed much, although they are beginning to. This is not the most successful in the book, since many historical linguists are likely to dismiss it as somewhat superficial, although it does bring into the picture a number of current controversies.
The author manages to bring a wide range of issues up to date and, for the first time, makes the subject of non-recombinant DNA from the Y chromosome accessible to the layperson. It is this DNA that gives information on descent in the male line - the counterpart of the maternal inheritance documented by mitochondrial DNA.
As an experienced science journalist who writes regularly for the journal Science , Olson has interviewed many of the researchers whose work is discussed. The result is a book that can be recommended to the general reader and the university student alike - in fact to anyone who wishes to find out what is going on in this fast-developing field.
The lack of a consolidated bibliography, however, is a deficiency. Although the book concludes with 35 pages of notes, including references to many relevant books and articles, a short bibliography with numbered notes, documenting Olson's various assertions, would have been helpful. For instance, in his well-balanced discussion of different views on the origins of the Indo-European language family he suggests that the ancient place names of Turkey are mainly non-Indo-European. A note at the rear to document that unexpected assertion would have been helpful. Again, in his up-to-date survey of the evidence for the peopling of Australia he states that "the genetic evidence seems to point to a relatively recent migration of people from India to Australia, perhaps as recently as 4,500 years ago". That too is an argument that merits documentation.
Perhaps the most refreshing aspect of Mapping Human History is the awareness that Olson shows for the social context in which such research takes place. As well as disposing briskly and effectively of racist thought, he devotes a chapter, "The burden of knowledge: Native Americans and the Human Genome Diversity Project", to debates surrounding the objections that some indigenous groups have mounted against DNA sampling. Here Olson, to my mind, may not be critical enough of the conventions that now allow commercial companies to patent genetic information belonging more (one might think) to the individuals providing the samples than to the western researchers patenting the sequences.
Archaeo-genetics, the study of the human past through the techniques of molecular genetics, is a new field. And while the availability of ancient DNA will always be restricted, samples from living populations are abundant, so that the continued development of research seems guaranteed. What we lack are some of the necessary concepts, and perhaps the statistical methods, to deal effectively with the long sweep of human demographic history. These will no doubt develop further over the next decade or two. Meanwhile, Mapping Human History is a good place to start for those wishing to know something of the state of the art.
Lord Renfrew is professor of archaeology, University of Cambridge.
Mapping Human History: Discovering the Past through our Genes
Author - Steve Olson
ISBN - 0 7475 6016 1
Publisher - Bloomsbury
Price - £17.99
Pages - 292