|Clan Mothers and Ancient Travelers|
|The Seven Daughters of Eve: The Science That Reveals Our Genetic Ancestry|
by Bryan Sykes
Posted: July 5, 2002
In 1991, a "traveller from an antique land" was found sticking out of the melting ice in the Italian Alps with a prehistoric axe by his side. Bryan Sykes, professor of genetics, was able to extract DNA from the 5,000-year-old bones and show an unbroken genetic link to the blood of a management consultant living in Southern England. While headlines trumpeted "Iceman's relative found in Dorset," Sykes started research that would lead to the discovery that all Europeans could trace similar genetic links back to seven maternal ancestors.
Sykes' book The Seven Daughters of Eve: The Science That Reveals Our Genetic Ancestry, which has now become available as a paperback, traces the history of Homo sapiens back to its origin through the genetic record present in our cells.
When Sykes, professor at the Institute of Molecular Medicine in Oxford, England, was asked to examine the Iceman's DNA, he was involved in researching how to recover genetic information from ancient human bones. Finding the same genetic sequence shared by the Iceman and a modern European led Sykes to redirect his research. He started examining DNA in present-day Europeans in the hope that he could uncover the history present in living genes. A particular type of DNA located outside of the cell nucleus provided the perfect object for his research.
Mitochondria, the tiny structures within our cells that produce energy, hold a piece of DNA that is always maternally inherited. A short stretch of this mitochondrial DNA has no obvious function and a high mutation rate: one mutation per 10,000 years. Sykes points out that although this rate "may seem incredibly slow, it is fortunately just about right for studying human evolution over the last hundred thousand years."
Unlike most DNA, this apparently neutral section can accumulate mutations because it has no obvious function, and thus no known ability to damage the working of mitochondria. Mitochondrial DNA has been handed down from mother to daughter virtually unchanged for tens of thousands of years. By counting the number of mutations in two sets of DNA, Sykes is able to calculate the time passed since two people shared a common maternal ancestor.
A group of people can also trace a common maternal ancestor, and the linking of two populations with common DNA heritage can reveal the time in history when they split off from each other. Throughout The Seven Daughters of Eve, Sykes reconstructs the genetic trail of human migration across the globe and frequently marvels at the great distances our ancestors covered across oceans and between continents.
In several chapters, Sykes manages a similar feat, moving from the investigation of the last Tsar's genes to following the geographic movement of Polynesian ancestors and exhuming Neanderthal fragments from an English quarry. We are introduced to deep-seated anthropological controversies and fundamental questions of human evolution. Did Homo sapiens spread out from Africa into Europe 100,000 years ago, or did modern humans evolve directly from Neanderthals who settled in Europe 1 million years ago? Was Polynesia populated from south-east Asia or from the Americas?
The geographic origins of the Polynesians had been disputed by European scientists for two hundred years when Sykes started taking blood samples there. Evidence pointed to boththe Americas, from which currents and winds flow towards Polynesia, and south-east Asia, which shares similar domesticated plants and animals. When the mitochondrial DNA was sequenced, Sykes clearly saw the same mutations pop up in coastal Asia and Polynesia.
Sykes also found a new mutation, which became more prevalent the further east he went. Concluding that the Polynesians began their journey near China, Sykes reveals a genetic trail with stops at many Pacific islands where new mutations show up: "By counting up the mutations and multiplying by the mutation rate [we] could estimate the length of time since the ancestral sequence first arrived."
In the second half of the book, Sykes applies the same logic to a collection of European samples and finds that he can separate DNA into seven clusters of similar mitochondrial sequences. He then links these clusters back to seven clan mothers from whom almost all Europeans are descended. What follows is not only the struggle Sykes went through to counter challenges presented by the scientific community and the narration of different phases of his research, but also seven final chapters in which he imagines the prehistoric lives of these women.
While The Seven Daughters of Eve provides an amazing show of how genetics can answer questions of history and anthropology, these chapters evoke a fascination with questions genetics has no answer for: Who were our ancestors and why did they travel so far?
Merete Rietveld is a freelance writer who lives in Palo Alto, California.