Wednesday, January 03, 2007
THE SEVEN DAUGHTERS OF EVE:
BY BRYAN SYKES
Since beginning his research career on mitochondrial DNA in the late 1980s Bryan Sykes has found himself propelled to the forefront of a virtual revolution in the way that genetics perceives the origin and spread of modern humans. This book(1), published in 2001, is a two part story. The first part covers how Sykes travelled from his early career as a medical researcher studying "brittle bone disease", also known as "osteogenesis imperfecta", an inherited disease of collagen formation found in cats, cattle, dogs and humans. As part of this the author gives a brief reconstruction of the history and science behind human genotyping in such chapters as 'From Blood Groups to Genes' and 'The Special Messenger'. Interspersed with this is a layman's explanation of DNA and, especially, mitochondrial DNA(2). Mitochondrial DNA is what Sykes research has been focused on. This is DNA that is inherited only (or at least 99.99%) through the maternal line. Sperm only contain mitochondria in their tails which are shed at the time of egg fertilization. As such they contribute only nuclear DNA to the new embryo.
What this means is that sequencing of mitochondrial DNA and its mutations can provide an estimate of the relatedness of individuals via their mothers, and their mothers, and their mothers,etc.. Research separate from that of Sykes and his group in this field has contributed to the idea of "Mitochondrial Eve", the mother of us all who lived in Africa(3) about 150,000 years ago.
After his excursion into the history and basic science of human genotyping Sykes describes the development of his field through an autobiographical account of his research. Not all of this is in chronological order, but the cast of characters that passes by is impressive. His early work was on extracting and amplifying mitochondrial DNA from bones only a few hundred years old at a time when the whole matter of the PCR technique was a matter of "shake and bake" chemistry in flasks rather than automated machines. From this it is on to proving the technique by research on golden hamsters. All of these pet animals are descended from one female first captured in Syria in 1930. Yup, it worked. The mitochondrial DNA of all pet and lab hamsters in the world was exactly identical. The story was true. They were indeed all descended from one mother.
From that humble beginning it's upward and onward. Tracing the presumed bones of the last Tsar and his family discovered in Ekateringburg in 1991 by comparison with living relatives of the Romanovs (at least a partial confirmation of the fate of Russia's last Royals and a disconfirmation of several claims to "Anasthasiahood"); genotyping of the "Iceman" found in the Italian Alps in 1991(and finding his living relatives in many present day Europeans); definitive proof of the South East Asian origins of the Polynesians (as opposed to the theory of their American origin); disproof (though often disputed) of the theory that Neanderthals interbred with early modern humans. All of this and more, all the time interspersed with clear explanations of the technical details involved and the disputes to which mitochondrial DNA testified.
All of this is perhaps a lead-in to what Sykes obviously considers his greatest triumph, his dispute with Luigi Luca Cavalli-Sforza, the acknowledged world expert on human genetics. The matter was the origin of modern European populations and whether they date deep into the paleolithic or whether they are the result of fairly recent "replacement" by agriculturalists "invading" from the Middle East. After a great amount of dispute and sound and fury Cavalli-Sforza came to accept Sykes' theories as derived from a study of mitochondrial DNA. In Sforza's case the clincher came from his own research on the DNA of the Y Chromosome, the "paternal line" as contrasted with Sykes' maternal line. Agriculture came to Europe by diffusion rather than invasion, and the present population of Europe traces back to women who lived in the paleolithic- despite a small contribution from the Middle East.
As a matter of fact Sykes traces the vast majority of present day Europeans back to just seven "founding mothers", the "daughters of Eve" of the book's title. Other researchers in the field have claimed that there are actually 10 to 12 "matrilines" present in Europe, and ongoing research is tracing more than 29 other "matrilines" across the world that descend from the original Mitochondrial Eve. The relationships between these clades(4) is a matter of present day dispute, but the general idea that individuals can trace their genetic ancestry to a small number of "founding mothers" is pretty well an established fact.
The new science of human origins founded on facts such as these is light years removed from the sort of "population origins" theorized about in faculties of anthropology even 25 years ago. Every population is a mosaic of origins in which different individuals trace their origins back to different "founding mothers", and in which the descendants of these mothers can easily live at opposite ends of the Earth. Combine this with the fact, as demonstrated by writers such as Richard Dawkins that various genes in a human individual may have totally different ancestors, and the concept of "race" becomes even more like a relic from a bygone age that only politicians can argue about.
The latter half of Sykes' book is devoted to an imaginative reconstruction of the everyday lives of each of the presumed daughters of Eve. They lived in different times and places, but their lives held more than a few commonalities. Despite the different climes and technologies available the lives of these women had much more in common than they had in difference. Sykes basically follows the consensus view of most modern archaeologists in that the lives or these women were indeed short and hard (in contrast to the Arcadian dream world of some ideologists), but they had more than their share of joys. The worlds that Sykes describes have a much greater feel of reality about them than the projected wishes of said ideologists who seem to envision "primitive people" as bodiless distillations of the ideologue's hopes and dreams, wistful ghosts who drift around busying themselves with "being one with nature" and playing whatever "joyful games" the modern ideologue may approve of (but never those he might disapprove of). On the other hand this paleolithic world may have always had the potential for intergroup conflict, but the consensus is that this was a rare event compared to the fantasies of the ideologues of "man the warrior". This also holds the aura of truth rather than ideological begging the question.
The second half of Sykes' book is admittedly not a work of science, but it is at least a journeyman's work of historical fiction.
1)'The Seven Daughters of Eve' by Bryan Sykes, W. W. Norton and company Ltd., New York, London (2001). ISBN 0-393-02018-5
2)See the following references on mitochondria and their DNA
iii)The Mitochondrial Genome
3) The actual homeland of Mitochondrial Eve is in dispute. The majority opt for the area of Ethiopia, Kenya and Tanzania. A minority feel that an Asian origin is more likely. What is hardly in dispute, however, is that this woman lived at a time of a "population bottleneck" when the number of proto-moderns was extremely low. Hence the fact that all of us today descend from her in a line traced through our mothers. It should also be noted that this woman was not the "single ancestor" that the term Eve suggests. It is pretty well certain that other women living at that time left descendants, but she is the only one whom we can trace back in an unbroken line of mothers. Many others left their genes to their sons to pass on. their nuclear DNA lived on, but their mitochondrial line was broken.
4)Clades are groups of organisms that are traced through common descent and not just through anatomical similarities.