You have your mother's green eyes. And perhaps your father's black hair. What you also inherited from you mother is a set of genes - mithochondrial DNA, or mtDNA - that is not a mixture of your parents genes (the technical term is recombination). If you are a male, you have also inherited unrecombined genes with your father's Y-chromosome.
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Because there is no gene "mixing" as each individual is conceived, these uniparentally inherited genes are passed from generation to generation unchanged, except when a mutation introduces a change. Studying the kinds and frequencies of these mutations in various human populations, geneticists may infer how related they are, and the likely paths of their past migrations. Knowing how often, on average, these mutations occur, geneticists may determine when human populations may have diverged, and link these events to the linguistic data and archaeological records.
It is no surprise that the study of the uniparentally inherited genes, the mtDNA and the Y-chromosome, has over the last 15 years revolutionized the understanding of human prehistory - so much that a name for this new discipline seems in order. I have seen both genetic archaeology and phylogeography used in this context. Steven Oppenheimer's large volume is perhaps the first effort to present and summarize this field of study to a non-professional reader, while still referencing (meticulously so) all the non-trivial research that underlies it.
Dr. Oppenheimer starts with a lucid description of the basics of genetics, mutations, the non-recombining genes and how these are uniquely suited to tracing human prehistory - something I attempted in the first two paragraphs of this review. Trust me, he does a much better job, but then again, he has more space. He certainly does an excellent job explaining the uniqueness of non-recombining, uniparentally inherited genes and how those have drastically altered and expanded our view of the human prehistory.
The rest of the book is structured roughly corresponding to the major phases of humanity's expansion in prehistoric times. In Chapter 1, The author discusses Africa, considered by many scientists as not just the most important cradle of humanity, but the only, and a very recent one. Oppenheimer is a unapologetic proponent of the Out Of Africa (OOA) theory - the hypothesis that modern humans have evolved in Africa fairly recently, in the last 200,000 years, and have since spread outside the continent without any mixing with archaic humans (such as the Neanderthals) who have expanded in the Old World earlier. This is a view shared by the majority of geneticists. However, there is a vocal minority of respected scientists who disagree with it, maintaining that there is evidence of genetic continuity with archaic humans who lived hundreds or thousands of years ago - or that, at least, the conclusions from mithochondrial and Y-chromosome studies are too broad and do not really contradict this hypothesis, known also as Out Of Africa Again and Again (OOAAA.) This is an exciting research question that may be answered by a new study or studies very soon.
In chapter 2, When Did We Become Modern, Oppenheimer also spends a considerable time arguing against the so-called Great Leap Forward - the concept that humans have indeed first become anatomically modern, but they did not become behaviorally modern until tens of thousands of years later, when around 60,000-50,000 YBP they colonized all of Africa, much of tropical and temperate Asia, and reached Australasia. The crucial component of the Great Leap Forward is thought to be the development of the neurological and perhaps physical capacity for full-blown languages; it appears to be associated with the spread of modern humans where the archaic ones did not venture (e.g., Australia), as well as the appearance of art and improved stoneworking techniques.
Oppenheimer does a complete, one may even say a passionate deconstruction of this argument, which he terms Eurocentric. He cites evidence of African art and advanced stone tools dating to before 100,000 years ago. He argues that the focus on European rock art is explained that Europe is by far the best archaeologically studied continent, and that its caves provided a unique environment for preserving ancient paintings (which no one would call primitive.) Oppenheimer further argues the impossibility of the Great Leap Forward occurring in Europe or Western Asia around 50,000 YBP, as there would not have been enough time to propagate the genes distinguishing behaviorally modern humans to South-East Asia and Australia, which were colonized by that time if not earlier. His argument is persuasive; there have been, however, recent discoveries of a gene (FOXP2), which is strongly correlated with the capacity for speech and language mastery. If these findings are confirmed, and the FOXP2 gene turns out to be relatively young, younger than the estimated emergence of anatomically modern humans, opponents of the Great Leap Forward theory like Oppenheimer will have some explaining to do - their hypotheses will need to be adjusted.
Oppenheimer proceeds to chronicle the migrations into Europe and the settlement of Asia. The European chapter is, in my view, one of the weaker ones - starting from the misleading title, Two Kinds of Europeans (there were likely many more than two, populating the continent via Anatolia, the Caucasus mountains, and Central Asia/Eastern Europe,) to the rather lacking synthesis of genetic, archaeological, linguistic and historical data, the synthesis that the author performs far better writing of South-East Asia (his specialty) and the Americas. Still, it was very interesting to learn how most pre-historic population of Europe has been driven to two or three refugia in the south of the continent during the harshest epoch of the last Ice Age. From there, humans have expanded throughout the continent when near-modern climate stabilized around 11,000 YBP, having covered remarkable distances and followed non-trivial migration paths. For example, it is thought that the mutation most common today in the extreme north of the continent, among the Saami, has originated in the westernmost glacial refugium of Northern Spain and Western France.
What the books suffers from, in my view, - and this is a minor gripe - is the unfortunate selection of the main title and some chapter titles. Though the Mithochondrial Eve is widely known as a metaphor for the most recent female ancestor of all living humans, it still has the completely inappropriate connotations of the biblical Adam and Eve. For one thing, the Y-chromosomal Adam (the most recent male ancestor) has likely lived tens of thousands of years after the mtDNA Eve, so these two were definitely not a couple. Secondly, while the genetic Eve is the ancestor of all living humans, she is not the only ancestor - it is just that in each of the 8,000 or so generations since her time some of her female descendants had reproductively successful daughters. The actual size of the early human population that contributed genes (not just maternally inherited ones) to today's humanity is estimated to be thousands or tens of thousands. Third, the identity of the genetic Eve (and Adam) is rather irrelevant, as this identity may and does change with the extinctions of long-isolated populations such as the Tasmanians. Lastly, Oppenheimer's book devotes as much if not less space describing male-related genetic markers. It may be that the catchy Real Eve title helped sales, but the more modest but far more accurate current subtitle, Peopling of the World, would have served better.
Rebecca L. Cann, Mark Stoneking & Allan C. Wilson. "Mitochondrial DNA and Human Evolution," Nature, 325 (1987), 31-6.
Templeton AR. 2002. Out of Africa again and again. NATURE 416 (6876): 45-51.. Excerpts at http://cogweb.ucla.edu/ep/Templeton_02.html
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