The Seven Daughters of Eve Read Free Page B

on from even the tiniest piece of tissue. A single hair or even a single cell was now all that was needed to produce as much DNA as you could ever want. The impact of Mullis’s brainwave on our bone project was simply that I decided to forget about working on the collagen protein, which would have been horrendously difficult, and use the newly invented chain reaction to amplify what, if anything, was left of the DNA in the ancient bones. If it worked, then we would get vastly more information from the DNA than we would ever have got from the collagen. We would be going directly for the DNA sequence itself, rather than inferring it from the amino-acids. Much more importantly, we would be able to study any gene, not just the ones that controlled collagen.
    At last we got an answer to our advertisement for a research assistant, and Erika Hagelberg joined the team. We were obviously not going to get anyone with previous experience in working with ancient DNA, because it had never been done before, but Erika’s degree in biochemistry, combined with research posts in homoeopathy and in the history of medicine, reflected a combination of a solid scientific training and the catholic interests which suited the project. Besides, she was the only applicant. Now we needed some very old bones.
    News came in during 1988 of an excavation going on in Abingdon, a few miles south of Oxford. A new supermarket was going up and the mechanical diggers had ploughed into a medieval cemetery. The local archaeology service had been given two months to excavate the site before the developers moved back in, so when Erika and I arrived, it was buzzing with activity. It was a hot and brilliantly sunny day and dozens of field assistants, stripped down to the bare essentials, were dotted all round the site scraping at the earth with trowels, rummaging around in deep pits or wading through water-filled trenches. Several skeletons lay half-exposed, encrusted with orange-brown earth, criss-crossed by strings which marked out a reference grid. As we gazed down at them, our prospects didn’t look at all promising. Having worked with DNA for several years, I was trained to treat it with respect. DNA samples were always stored frozen at 70° below zero, and whenever you took DNA out of the freezer you were taught always to keep it in an ice bucket. If you forgot about it and the ice thawed then you had to throw the DNA out because, so everyone assumed, it would have degraded and been destroyed. No-one imagined it would last for more than a few minutes on the laboratory bench at room temperature, let alone buried underground for hundreds or even thousands of years.
    Nevertheless, it was worth a try. We were allowed to take three thigh bones from the excavation away with us. Back in the lab we had to make two decisions: how to get the DNA out, and what section of DNA to choose for the amplification reaction. The first was easy enough. We knew that if there were any DNA left at all it would probably be bound up with a bone mineral called hydroxyapatite. This form of calcium had been used in the past to absorb DNA during the purification process, so it seemed quite likely that the DNA would be stuck to the hydroxyapatite in the old bones. If that was the case, we had to think of a way of disengaging the DNA from the calcium.
    We cut out small segments of bone with a hacksaw, froze them in liquid nitrogen, smashed them up into a powder, then soaked the powder in a chemical which slowly took out the calcium over several days. Fortunately, when all the calcium had been removed, there was still something left at the bottom of the tube – a sort of grey sludge. We guessed this was the remnants of the collagen and other proteins, bits of cells, maybe some fat – and, we hoped, a few molecules of DNA. We decided to get rid of the protein using an enzyme. Enzymes are the catalysts of biology, making things happen much more quickly than they otherwise