As a geneticist, my professional interest in sex began over a decade ago when I first started to use that science to unravel some of the secrets of the human past. I chose as the instrument to navigate these mysteries a piece of DNA which is inherited purely down the female line, passed from mother to daughter for generation upon generation directly from our ancestors to the present day. This choice was made not out of any greater interest in women than in men on my part but because of its special properties. What this particular stretch of DNA revealed was not so much a history of our species as a history of women. And what a history it is. I was able to show that each of us is connected by unbroken maternal threads, traceable with DNA, to one of a few ancestral women living thousands, even tens of thousands of years ago. I was also able to track the movements of our ancestors across the globe and solve some of the riddles that had puzzled scholars for centuries - among them the origin of the Polynesian islanders, the fate of the Neanderthals and the nature of the first colonization of Europe by Homo sapiens before the last Ice Age.

I was well aware that, because the DNA I had used was maternally inherited, my interpretation of past events was based entirely on the genetic history of women and would need to be confirmed and complemented by an equivalent genetic history of men when that became technically feasible. However, I was confident that the main events had been interpreted correctly and that, although they might well be revised, the conclusions I had reached would not be substantially altered when the history of men came to be known. After all, men and women had to have been in the same place at the same time. I was quite content to leave unravelling the history of men to others and began to turn my attention to other projects. Then a chance event occurred that changed the course of my research and sent it spinning off in a new direction. And it brought the genetics of men right back into sharp focus.

As so often, the sequence of events began with a phone call - a call which was, in itself, nothing out of the ordinary. I work in the Institute of Molecular Medicine in Oxford as a professor of genetics, and from time to time I am asked to give talks on the subject to pharmaceutical companies. This particular call was an invitation from Glaxo-Wellcome (now part of Glaxo-SmithKline) to join a group of other scientists from Oxford at a conference at their company headquarters. Like many drug companies in the mid-1990s, Glaxo-Wellcome had realized that the discovery of new genes by the Human Genome Project, then well under way, would identify new targets around which to design drugs. If the genes for the big killers - heart disease, diabetes, cancer and so on - could be found somewhere in our DNA then they might show us what was going wrong when these diseases occurred, and new drugs could be designed to correct the mistakes. That, at least, was the theory.

What makes this particular invitation relevant to my story is that the chairman of Glaxo-Wellcome at the time was Sir Richard Sykes. As you can imagine, I was asked several times by the organizers from Glaxo-Wellcome in the run-up to the meeting whether Sir Richard and I were related. The only Richard Sykes I knew at the time was my own son; as far as I knew, their chairman and I were not connected at all. You can tell from Sir Richard's accent that he was brought up in Yorkshire, in the north of England. I, on the other hand, spent my childhood in London and have the accent to match. The only similarity between Sir

Richard and myself, other than our both having trained as scientists, is that we have the same surname. I thought no more about it.

When I got into the car which had arrived to take me to the conference, the driver asked me the same question again. I don't know why, but this time, as I was about to repeat my simple denial, I suddenly had a thought. Maybe Sir Richard and I were related after all, but without realizing it. And, more to the point, maybe I could prove it by a genetic test. I asked the driver to wait, rushed back into the Institute, grabbed one of the small brushes which I used to collect DNA samples and ran back to the car. Sir Richard was going to be at the conference; I would ask him for a DNA sample and then compare it to my own. If he and I really were related then we would both share one very special piece of DNA. We would have the same Y-chromosome, that piece of DNA which every father gives to his son.

The following day, back in my laboratory, I took the small brush from its package. Invisibly attached to the nylon bristles were the cells that Sir Richard had brushed from his inner cheek the evening before. Though there were only a few hundred of them, they would be more than enough for me to get a genetic fingerprint of Sir Richard's Y-chromosome. Taking great care not to touch them, I cut the bristles away from the stem of the brush and dropped them into a small test tube. The cells had dried out overnight, but DNA is such a tough material that I had no doubt it would still be intact. After all, in previous research I had managed to get DNA out of human fossils over ten thousand years old, so I wasn't worried about a sample that had only been 'dead' for a few hours. Sir Richard's Y-chromosome lay at the centre of his cells and I needed to strip away the rest of the cell to get at it. Because DNA is so robust, I could use quite brutal chemistry to do this and the harsh treatment started straight away. I covered the cells with a few drops of water, then boiled them hard for ten minutes. This rehydrated the cells and burst through the delicate membrane that surrounds the nucleus, the very centre of the cell where his Y-chromosome was hiding. Now, after the boiling-water treatment, it was naked and exposed and could be minutely examined by the intricate molecular reactions that revealed its precise genetic fingerprint. I will say much more about this process later on, but for the moment all we need to know is that it worked perfectly on this important sample.

After a couple more days' work I had got Sir Richard's detailed genetic fingerprint from his purified DNA. Then, on my computer, I called up my own Y-chromosome fingerprint, which I had
read several months previously. It resembled a bar-code, a series of dark and light bands that define a unique identity. I lined it up with Sir Richard's and went along the pattern, one bar at a time. They were all exactly the same. Our Y-chromosomes matched perfectly.

It was proof that the two of us were related. But how? Both Sir Richard and I had inherited our Y-chromosomes from our fathers, who had inherited it from theirs, who had inherited it from theirs, and so on back in time. Our Y-chromosomes were tracing two direct lines of paternal ancestry which went further and further back into the past. Since our Y-chromosomes were identical, this had to mean that the lines we each traced back through our fathers, our grandfathers, our great-grandfathers and so on converged at some point on just one man. This man, whoever he was, was our common paternal ancestor, a man to whom both Sir Richard and I could trace, through our Y-chromosomes, an unbroken genetic link. Since we had also inherited our surnames via the same route it was extremely likely that this man, our common ancestor, was also called Sykes. At a stroke, our Y-chromosomes had proved a connection between us that no documents had ever suggested. Even now, years later, we still don't know precisely how we are related, and it might take years of patient work to trace the connection through records of births, marriages and deaths - if it could be done at all. But somehow that doesn't seem to matter. The genetic thread is direct and continuous, regardless of the generations of men through whom it has passed.

Having shown the genetic link between Sir Richard and myself, I began to wonder how many other people called Sykes were similarly related. Could it possibly be that we all were? I am ashamed to say that at the time I knew next to nothing about the origin of my surname. About all I did know was that my grandfather had been a soldier in the First World War and that his family had come from somewhere in Hampshire in southern England. As far as I was aware, there was no connection with Yorkshire that could possibly link my family to Sir Richard's. Had my family moved from Yorkshire to Hampshire at some time in the past? Or had Sir Richard's gone in the opposite direction, from Hampshire to Yorkshire? Where did most of the Sykeses live anyway? I didn't have a clue.

About this time I got a letter through the post at home. This was an invitation to purchase the grandiloquently entitled Book of Sykes. Normally this kind of circular would have headed straight for the bin but, curious for the first time to know more about the name, I sent off for the book. Expecting an in-depth exploration of the history of the family, I received instead a folder with some very general blurb on surnames, a suspicious-looking coat-of-arms and, at the back, a list of names and addresses of Sykes men, arranged by county. Had I been interested only in the name, I would have been disappointed. But, though I was none the wiser about its history or origins, the list at the back was just what I needed. Looking through it I saw at once that there were far more Sykeses living in Yorkshire than anywhere else. So it looked as though it had been my ancestors who had been the ones to move rather than Sir Richard's. I picked 250 Mr Sykeses at random from Yorkshire and the neighbouring counties of Lancashire and Cheshire, and wrote to each of them asking for a sample of his DNA. Since I was a Mr Sykes writing to other Mr Sykeses it did not feel so much of an intrusion as it would otherwise have done. Enclosed with each letter was a DNA brush, and within a month I had received back about sixty samples of Sykes DNA.

Let me say at this point that I now know from bitter experience that, although there is nothing more fascinating than your own family history, there is nothing more tedious than someone else's. So please forgive me while I tell you some things about the Sykes family. I do it only to illustrate, not to inform, and when I have finished you are free to forget all about us.
I had done a little more research on the name and discovered that Sykes derives from the Yorkshire word 'sike', which is a particular kind of moorland stream. No magnificently gushing torrent, this; a sike is more of a slow trickle in a ditch, and sikes often marked boundaries between adjoining plots of land. If I was hoping to prove that all living Mr Sykeses were related and ultimately traced their origins back to a single founder, this news was not encouraging.

Other than among the aristocracy, most English surnames were introduced around the thirteenth century, principally as a tool of estate management. By this time pretty much the whole country was divided into large feudal estates, a direct legacy of the Norman invasion in 1066 by William the Conqueror, who handed them out to his friends and supporters. A feudal lord controlled all the land on the estate and distributed the agricultural land among the tenant farmers, whose rents kept him and his immediate family in the grand style to which they very soon became accustomed. This was a highly regulated structure, and detailed records were kept- of which many still exist - listing the size and rental of each parcel of land along with the name of the tenant.

The trouble was that, without surnames, it was almost impossible for the estate officers to keep track of events. Within a small village, where everybody knew everybody else, it was easy for the residents to cope with several people having the same name. They knew them as individuals and often by a nickname as well. But the estate managers had huge difficulties. It was often impossible to tell which John or Adam or Mary or Maud was which. Their solution was to differentiate between people with the same name by adding another name - a surname. Soon afterwards these new surnames became hereditary. By the middle of the thirteenth century, tenant farmers were permitted to pass on tenancies to their sons when they died, so it was natural under the circumstances for the surname to become hereditary, just like the tenancy itself. It was this very practical aspect of medieval book-keeping that lay at the origin of most English surnames. From these bureaucratic beginnings, eventually every man was given a surname; on
marriage, women took the names of their husbands. Sometimes these surnames were derived from an occupation - like Carpenter, Smith or Butcher; sometimes they evolved from a nickname, often a descriptive one, such as Redhead or Smallpiece. Other surnames merely added '-son' to the name of the father to form patronymics like Johnson or Adamson. A fourth category of names were derived from a feature of the landscape - Hill, Bush, Wood and, in Yorkshire, Sykes.

That was the discouraging prospect. Since there were literally thousands of sikes in Yorkshire, the chances that only one man had decided to adopt 'sike' as his surname seemed extremely slim. Even though the Y-chromosome results certainly suggested that at least Sir Richard and I were descended from the same man, the likelihood of a large proportion of the random samples I had collected from other Mr Sykeses being similarly related seemed remote indeed. However, when I deciphered their Y-chromosome fingerprints the results were truly amazing. Fully half of the Sykes samples, randomly collected from the three counties of Yorkshire, Lancashire and Cheshire, had exactly the same fingerprint. There was only one possible explanation for these spectacular and unexpected results. The volunteers, including Sir Richard and myself, who have the same Y-chromosome fingerprint, must have inherited it from a common ancestor. All of us must be able to trace a direct father-son lineage back to one man. But who was this man? Was he the original Mr Sykes? And, equally important, what about the other half of the sample, the men who did not share this Y-chromosome fingerprint?

Let's tackle the second question first. The Y-chromosomes that didn't match the 'Sykes' fingerprint, as I was now starting to call it, were split into two categories. A few, while not exact matches, were very close to the 'Sykes' Y-chromosome. The others had very different 'bar-codes' and were completely unrelated to it as far as I could see. Not only that, they were not obviously related to one another either. There were no other clusters of related Y-chromosomes to suggest we had found the descendants of a second 'original' Mr Sykes. What explanation was there for this pattern, where half of the Sykes men shared the same Y-chromosome fingerprint and the other half had a mixture of Y-chromosomes with no obvious relationship to each other?

At this point in the narrative we need to introduce the factor to which geneticists politely refer as 'non-paternity' - the term used when a child's father, the name on the birth certificate, is not the biological father. When a son bears the surname of his father but does not carry his genes there are only a few explanations available. The most straightforward, and innocent, is that the son has been adopted and taken the surname of his adoptive father. Of course, the same happens to adopted girls, but they will most likely not transmit this name to their children and they will certainly not pass on a Y-chromosome either. Y-chromosomes are only ever passed between father and son. Women just don't have them. The second explanation is that the entire family adopts a new surname. This was not a common practice in medieval England but it certainly was in Scotland, where a man often took the name of the clan chief on whose lands he lived or in whose army he fought without being related to him. That leaves us with the third and final explanation for the discordance between surname and Y-chromosome - infidelity by, or possibly rape of, the woman. Biologists have a rather more brutal name for it - extra-pair copulation. If a woman has a child with a man other than her husband and if that child is brought up within the family and is given the family name, the link between name and genes is broken. If the child is a boy, he will inherit his father's surname but not his Y-chromosome. That will have come from his mother's lover, or from her assailant, and not from her husband. When he has sons of his own, it will be this man's Y-chromosome that is passed on. Even if there are no non-paternity events in later generations, the link between the Y-chromosome and the original surname cannot be rescued. It is severed for good.

From our admittedly limited survey, the Sykes Y-chromosomes fall into two roughly equal categories. The first group were very closely related to one another and are almost certainly inherited, without interruption, from one original Mr Sykes. The other half of our volunteers had inherited Y-chromosomes which are very different from the 'original' Sykes chromosome and also from one another. These Y-chromosomes could have become associated with the name through infidelity, rape or adoption at some point since the name started. Or they might be the Y-chromosomes of several different 'original' Mr Sykeses, each passed down to the present day through a direct paternal line unbroken by non-paternity events. From this evidence alone it is impossible to tell the difference;
however, if they were from different originals, none of them had done anywhere near as well as the main Sykes chromosome.
Though there is no way of formally distinguishing these different possibilities, I thought we should be able to work out a figure for, if you like, the accumulated rate of non-paternity events. This would be an estimate of the proportion of non-paternity, of whatever type, that had occurred since the thirteenth century to give us the present pattern, with half the Sykes men sharing the same Y-chromosome signature and the other half showing a mixture of apparently unrelated genetic fingerprints. I needn't trouble you with the calculation; the answer comes to 1.3 per cent non-paternity events per generation. It means that for over seven hundred years, the average rate of adoption and illegitimacy could be only just over 1 per cent in each generation. Had it been much higher than this, the pattern we see among modern Sykes Y-chromosomes would have disintegrated long ago. Put another way, it means that 99 per cent of Mrs Sykeses have been very well behaved, or very lucky, for the last seven hundred years. In fact, since this figure also incorporates the possibility of other independent founders of the name it is the maximum estimate for non-paternity, and when you bear in mind that some of these events would have been genuine adoptions, the illegitimacy rate falls yet lower still. How does that compare to rates of non-paternity these days? Surprisingly, there is no universally accepted value for the current rate, but the range of estimates (5-30 per cent) in different studies in the UK are all much higher than the historical values obtained from the Sykes results.

Even with the difficulty of distinguishing the influence of non-paternity events from that of different independent founders, the overall result was staggering. Most, if not all, the volunteers from the three counties of Yorkshire, Lancashire and Cheshire had got the name from one man. And half of them still carried his Y-chromosome. Had I been incredibly lucky with the name Sykes? I don't think so. Over the past two years I have replicated this study with dozens of names. Not all of them show as tight an association between surname and Y-chromosome as Sykes, but most do and some are even more impressive. In one name, to which I shall return in a later chapter, fully 87 per cent of present-day holders have the same or very closely related Y-chromosome. From what I can see so far, the majority of surnames, in England anyway, are very clearly linked to one or a very few Y-chromosomes.

Of course, there had been luck involved: not so much in that no other name would have worked as well - it would - but for a completely unscientific reason. Had the chairman of Glaxo-Wellcome not been a Sykes, I would never have thought of doing the study in the first place. A second piece of good fortune was that Sykes is a Yorkshire name and Yorkshire just happens to be the home of one of the best surname experts in the whole of England - Dr George Redmonds. Without George, the Sykes Y-chromosome study would have ended up as a cold and formal scientific report; interesting, to be sure, but with no real connection to the history and the landscape that I was now aware had been the home of my genetic ancestors for the best part of a thousand years. Sykes country, as I now felt entitled to call that part of West Yorkshire south-west of Huddersfield, is a landscape of barren moorland intersected by steep-sided river valleys. From the top of the high moors the area looks almost deserted, with hills rolling away into the distance in every direction. Slightly lower down the slopes are the hamlets, the clutches of weavers' cottages each clustered around a farmhouse. Lower still, confined to the valley floors and completely out of sight from the hilltops, are the old mill towns, fully urbanized, noisy and dirty.

George lives high up on the moors and his knowledge of the area - its landscape, its history and particularly the histories of its families - is nothing short of encyclopaedic. A drive round this rugged landscape with him brought it vividly to life. The unnoticed line of a broken dry stone wall on a distant hillside became the failed attempt of a medieval farmer, pushed higher and higher out of the valleys, to cultivate the poorest land. One craggy peak - Wolfstone Heights - is no longer just a name on the map but recalls a time, not so very long ago, when there really were wolves living on the moors.

George and I first met when we were making a series of radio programmes for the BBC on the subject of surnames, genes and genealogy (produced by another Sykes - Sandra) and George began to search for the earliest records which mention the Sykes name. Within a short space of time, he had unearthed a reference in the court rolls of 1286 to a Henri del Sike. George showed me some of these records, and their condition is quite remarkable. Inscribed on parchment, made from calf skin, they are strong enough, even after several hundred years, to be handled without disintegrating. Had they been written on paper instead, they would have crumbled into dust long ago. The particular court record that George had found referred to a tenancy dispute involving Henri del Sike in lands near to the village of Flockton, a few miles south of Huddersfield. The village is still there, and there are still Sykeses in Flockton, but a quick trawl through the electoral roll showed that there were far more in the small town of Slaithwaite, about nine miles distant. Slaithwaite, George already knew, was a much younger settlement than Flockton. It is situated at the bottom of a steep-sided valley, on the banks of the River Colne. These valleys were thickly wooded in medieval times, marshy and full of wild animals. This made them difficult to farm, so the hamlets and villages were established higher up on the valley sides where the land was well drained and largely clear of trees. It was only much later, in the eighteenth and nineteenth centuries, when weaving and textile manufacture became industrialized, that the valley floors became densely settled. The dark mills, thirsty for water to wash the wool and to feed the steam engines that powered the looms, needed to be built close to rivers.

The obvious question which George asked was this. Were the earlier Flockton Sykeses related to the Sykeses of Slaithwaite? He had discovered evidence of Sykeses living between the two settlements in the fourteenth century and had found a convincing explanation of why they might have moved away from Flockton. The Black Death - bubonic plague - had scythed its way through the population of Europe first in 1348 and then in subsequent epidemics of diminishing ferocity over the next hundred years. The initial epidemic killed between one third and one half of the population in the space of eighteen months. It is hard to imagine the terrible effects of an epidemic on that scale among our ancestors. No family escaped as fear and death swept across the land like a swift black shadow. After the epidemic burned itself out, unable to find sufficient susceptible victims still living to sustain it, the survivors found themselves in a new economic landscape. Faced with an acute shortage of labour, the feudal lords were forced to improve the wages and conditions of their tenants and serfs. Land cleared of its occupants by the Black Death became available to new occupants. In George Redmonds' opinion, it was the opportunity to settle on new land which had persuaded some of the Sykeses to leave Flockton and seek their fortunes elsewhere. Now the genetics suddenly gave George the opportunity to test out his idea. If the Sykeses in Slaithwaite had come originally from Flockton, then the Y-chromosomes of the two groups ought to match. I wrote to the Sykes men in Slaithwaite and Flockton asking for samples of their DNA - and, when we analysed their Y-chromosomes, we found that the genetic fingerprints were absolutely identical. George's hunch had been right, proved beyond any doubt by this new genetic test.

I wanted to see the original site near Flockton which George had linked to the very first Sykes in the records. It was a cold day in early April when we got out of the car next to a stream which ran along a valley floor. The trees were not yet in leaf and great oaks stood naked in the green fields opposite. These pastures led up to a ridge about three hundred yards away where the village of Flockton itself is strung out along the brow of the hill just as it has always been. To our left, beyond a dry stone wall, an uncultivated croft was alive with the golden flowers of kingcups in the boggy ground close to the water. The stream itself was clear and bubbling but the bed of the river was dead, choked by the rust-coloured deposits of ochre, the still polluting effluent of long-abandoned iron-ore mines.

A track led off across the stream and George led me down it between tall poplar and aspen trees which hugged the water. At a bend in the watercourse stood the ruins of an old mill, abandoned long since. George had pinpointed this particular spot by finding that Henri del Sike had the tenancy of land on both sides of the stream, which lay in different parishes. There was no sign of the farmhouse which my ancestor, the very first Sykes, had occupied, but even so, it felt quite extraordinary to be here. Looking around at the old mill, the track and the stream, it seemed that nothing in the landscape had greatly changed. Nor had it. The field and croft boundaries were as they had been in the late thirteenth century when Henri del Sike was living here. As I stood, I could almost hear the voices of children - my ancestors - laughing as they threw pebbles into the stream. Without the DNA evidence, it would have been an interesting enough experience to see where the first recorded Mr Sykes lived. But I would have felt detached from it. I would have known there was a connection of a sort between the place and me, but it would have been a connection made through the mind, the rational conclusion of a process that matched the name on my birth certificate with another name on a piece of yellowing parchment. But to know that the Y-chromosome that I carry in all my cells had actually been here, in this place, in the fields beside the stream, was a completely different sensation. Now it felt as if I were experiencing the history of a real part of myself, a place where some of me had actually lived. And, of course, it had.