Free The Seven Daughters of Eve by Bryan Sykes

particular. If it did, then many of the mutations would affect the performance of the mitochondrial enzymes. This does sometimes happen when mutations hit other parts of the mitochondrial DNA outside the control region; there are some rare neurological diseases which are caused by mutations in genes that disable essential parts of the mitochondrial machinery. Because they are so damaged, these mitochondria do not survive well and are only very rarely passed on to the next generation. So these mutations gradually die out. The control region mutations, on the other hand, are not eliminated, precisely because the control region has no specific function. They are neutral. It appears that this stretch of DNA has to be there in order for mitochondria to divide properly, but that its own precise sequence does not matter very much.
    So here we have the perfect situation for our research: a short stretch of DNA that is crammed full of neutral mutations. It would be much quicker and cheaper to read the sequence of the control region, just five hundred bases, than the entire mitochondrial DNA sequence at over sixteen thousand bases. But was the control region going to be stable enough to be useful in examining human evolution? If the control region were mutating back and forth at a great rate at every generation, then it would be extremely difficult to make out any consistent patterns over the course of longer time spans. We knew already from the work of Allan Wilson that if we were going to dig down deep into the genetic history of our species, Homo sapiens , using mitochondrial DNA, we needed to cover at least 150,000 years of human evolution – say 6,000 generations at twenty-five years per generation. If mutation in the control region were too frantic or erratic, it would be very hard, if not impossible, to distinguish the important signals from all the incidental, irrelevant changes after a few generations. We needed a way of testing this before embarking on the time-consuming and expensive commitment of a large study of human populations. How could we best do this?
    Ideally, I wanted to find a large number of living people that could be proved to be descended through the female line from a single woman. In the course of my medical genetics research on inherited bone disease, I had worked with several large families; so now I took out the charts on which I had recorded their pedigrees. Although these went back several generations, there were depressingly few continuous maternal lines connecting the living members of these families. I could ask for the families’ help to put me in touch with relatives who were not shown on the charts; but it would be a long business. Still, there seemed nothing else for it, and I began to dig out their names and addresses. On my way back home that night, while I was thinking about something else, I experienced one of those rare moments when an idea suddenly arrives from the recesses of the mind, goodness knows how, and you know within a millisecond that it is the answer to your problem, even though you haven’t had time to work out why. I suddenly remembered the golden hamster.
    When I was a small boy, I read in a children’s encyclopaedia that all the pet golden hamsters in the world were the descendants of just one female. I can definitely say that I had not thought about this again over the intervening decades. And yet the idea surfaced now. I do remember thinking at the time that the story couldn’t possibly be true. But what if it were? This would be the ideal way to test out the stability of the control region. All the golden hamsters in the world would have a direct maternal line back to this ‘Mother of all Hamsters’. It follows that they would also have inherited their mitochondrial DNA from her, since it is passed down the female line in hamsters just as it is in humans. All I had to do was collect DNA from a sample of living hamsters and compare their control