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http://www.nytimes.com/2004/06/08/science/08conv.html
A CONVERSATION WITH BRYAN SYKES
Is Genghis Khan an Ancestor? Mr. DNA Knows
By CLAUDIA DREIFUS
Published: June 8, 2004
Wherever Dr. Bryan Sykes travels, he carries little swabs for collecting genetic material from strangers.
Dr. Sykes, a human genetics professor at Oxford University and a science adviser to the British House of Commons, loves showing people the astonishing history hidden in their DNA. Zip! A quick swipe of the inner cheek. Three weeks later, a report arrives from Dr. Sykes's laboratory with surprising news that you have, say, a West African ancestor or a kinship to Genghis Khan.
At the moment, Dr. Sykes is collecting swabs from everyone he meets named "MacDonald," to determine the migratory patterns of each branch of the Scottish clan. A reporter was astonished to discover that she has a common ancestor with "Otzi," the prehistoric Ice Man of northern Italy.
Playful projects of this sort might obscure the fact that Dr. Sykes, 56, is one of the world's most acclaimed geneticists. In the 1980's, he and his Oxford colleague, Robert E. Hedges, discovered ways to extract DNA from fossilized bones; ever since, he has been using these methods to unravel the genetic history of humans.
His book about the origins of modern European women, "The Seven Daughters of Eve," was an international best seller in 2001. His second work, "Adam's Curse: A Future Without Men," published in April, is a discouraging look at men and their fragile Y chromosome, which he sees as "a graveyard of rotting genes."
Q. "Adam's Curse" reads almost like a polemic against the Y chromosome. What do you have against it?
A. I don't have a high opinion of it, do I? I'm certain I couldn't have written this book had I been a woman. I would have been accused of having a feminist agenda, and I don't. In some passages, I feel distinctly sorry for the Y chromosome. However, if you trace the Y chromosome's fingerprints back through human history, you see that it reports some very unpleasant behavior. Take Genghis Khan's Y chromosome, which is now found in 16 million men in Central Asia. It started as a single copy from the man himself in the 12th century. What drove this? Well, when he conquered a territory, he killed the men and systematically inseminated the most attractive women. A thousand years later, his Y chromosome has survived and proliferated, which is sexual selection on a very grand scale.
In fact, whenever geneticists look at evolutionary diagrams, they see some frequently occurring Y chromosomes, not closely related to others. These genetic "explosions" are the legacy of a relatively few very successful men who have supplanted the Y chromosomes of their contemporaries, as Genghis Khan did. My guess is that the Y chromosome of every living man has spent at least one generation in the testis of a warlord.
Q. Still, you write that the Y chromosome is flawed and doomed, and predict that it will disappear. Why?
A. Because, unlike all other chromosomes, the Y doesn't get a chance to mix with any other chromosomes. It doesn't get to exchange DNA with the others, the opportunity which sex itself provides, which is a sad irony since it is the Y that differentiates the male from female in the first place. It gets passed on from one male to another, and it cannot repair mutations through genetic recombination.
Moreover, the Y chromosome is subject to a higher mutation rate than other chromosomes because it is perennially confined to the male germ line. Male germ line cells and their DNA divide very, very fast to keep up with sperm production. Most mutations occur when DNA divides. So the Y is intrinsically unstable. By my estimate, in about 5,000 generations - 125,000 years - male fertility will be roughly 1 percent of what it is now. Mutations in Y chromosomes are already known to reduce male fertility. So I see a slow decline in men's fertility until, eventually, men can no longer breed naturally.
Q. Should we be worried now?
A. There are more immediate problems in life, although 125,000 years is just a fraction of a second in the overall evolution in our species. And there will be things that can be done; we could take the essential genes from the Y chromosome and put them on regular chromosomes, out of harm's way.
A more radical possibility involves eliminating males from the reproductive process. Japanese researchers have just created a mouse from fusion of two eggs. On the face of it, the mouse developed normally. There was no male involvement at all. The triumph of this experiment is that it overcame an inbuilt system called genetic imprinting, which hitherto had prevented mammals from reproducing by parthenogenesis.
I feel sure that humans will one day be able to reproduce by the fusion of two eggs. The children will always be girls, and they will have the same genetic mix as any other girl. This is very feasible, and I think will happen in my lifetime. Importantly: This is not reproductive cloning because you are not making a genetic copy of a person. Here you are creating an entirely new individual with a mixture of genes from two parents, though both of them are female. I could see where two homosexual women, who want to become the biological parents of a child together, might consider doing this.
Q. Why don't we hear much anymore about a "gay gene"?
A. You are referring to research on gay men and their families published in 1993 by Dean H. Hamer and his team, who located on the X chromosome a gene controlling male homosexuality. Though this was subsequently replicated by Hamer, another study along similar lines failed to confirm the association. Since then, no one has tried to take the "gay gene" any further.
On purely genetic grounds, I never liked the idea of a "gay gene" since it is very hard to see how such a gene could have survived and spread among our ancestors since it is bound to have been eliminated if homosexual men had fewer children than their heterosexual contemporaries. Genes that even slightly reduce their chances of getting passed on to the next generation have very short careers.
Q. You are known as a founder of bioarchaeology. What is this?
A. It's a name for something my colleagues and I have been doing since the 1980's; we use a range of biological techniques on archaeological material so that we can learn more about past populations.
The field came to prominence because we've been able to use these techniques to isolate and amplify DNA from very old bones. I've gotten to work on the frozen body of the 9,000-year-old Ice Man who was found in the Italian Alps. Through DNA testing, we discovered he was related to a good friend of mine!
Beyond the interesting science, what has fascinated me about this work is how many people have grown interested in the genetics of their ancestors. People are absolutely fascinated by what the mitochondria, with its maternally inherited DNA, and the Y chromosome can reveal. As genetic studies have advanced, the Y chromosome has revolutionized genealogy because of the strong correlation between Y chromosomes and surnames. For instance, I've tested hundreds of people named "Sykes" and found that roughly 70 percent of us have the same Y chromosome, and therefore, must be descended from one man.
(Ñîîáùåíèå îòðåäàêòèðîâàë ret 10 èþíÿ 2004 10:52)
