by Steve Jones
How far was your birthplace from that of your partner and how far apart were your mother and father, and your grandmother and grandfather on each side, born? In almost every case, the distance has increased over the generations and continues to do so (my wife and I first saw the light five thousand kilometres apart, my mother and father about five; as my students say, it shows). Even in the Middle East, that centre of sexual conservatism, education, affluence and the chance to travel mean that DNA is on the move. A series of Israeli Arab villages experienced a drop in the incidence of cousin marriages from about a quarter in the 1980s to a sixth at the millennium. The same is true in Jordan, Lebanon and Palestine.
In the past, hurdles in the mind kept people apart. If the few remnants of hunter-gatherer tribes still left are any guide, any attempt to join another group was likely to be met by death. European frontiers, too, are marked by genetic steps, with a deeper difference in identity between the bluff beer-drinkers of the north and the vapid wine-bibbers of Spain and Italy. The continent’s long history of staying at home is manifest in its surnames - those windows into sexual history - as much as its genes. A pedigree of names used to fit well with national boundaries with the Camerons more or less confined to Scotland and the Zapateros to Spain. Spain itself has the most localised patterns and can also boast of the commonest surname in Europe - García. In terms of names and genes, Paris is the most diverse city in Europe.
Names - and the DNA that accompanies them - are on the move. In 1881, Darwin’s last full year, and the date of a British census, his surname was borne by about one Briton in fifty thousand. Its origin is Welsh, from ‘derwen’, or oak; a name transferred to the River Darwen in Lancashire. In his day its headquarters was in Sheffield and its surrounds, where the tag was eight times more common than in Britain as a whole. Almost all those who bore it lived within eighty kilometres of the city (the Joneses - the group with the second most common British surname after Smith - were still, in those happy days, more or less confined to Wales, where in some villages they formed a majority). By 1998, the naturalist’s name had spread northwards to find a new centre in Durham, with secondary centres across the north from the Mersey to the Tyne and a minor outbreak in Herefordshire. The Joneses, too, had migrated, with a grand smear across the Welsh borders, north-west England and as far south as London. No longer must a Darwin or a Jones, or anyone else, marry - as so many once did - someone from their own family for lack of choice. Instead they come into contact with a diverse set of potential partners. The proportion of shared names in the marriage records of a typical English village has gone down by around 2 per cent a year even since the mid-1970s and by even more since the publication of The Origin of Species. Sheffield, once its author’s nominal capital, now has scores of new names from across the world.
The United States has gone further down the road to homogeneity. Its telephone directories contain a million different surnames. Some remnants of history remain, with Wisconsin full of Scandinavians while the phone books of New Mexico, Colorado and Texas reveal the presence of many Spanish immigrants. Even so, the general picture is - unlike Europe - one of national uniformity. One in eight Americans is foreign-born (and in California twice as many), and Americans move home, on average, a dozen times in a lifetime, with ten million each year shifting from one state to another. Such frantic migration soon mixes up names, and, in time, genes. The power of the train or plane as an agent of evolution will soon even out yet more of man’s genetic differences.
Almost everywhere, biological frontiers are becoming porous. An era of uniformity is at hand as vast hordes of people move in search of work or sunshine and, in the end, sex. In Britain, the proportion of those born abroad has doubled in the past fifty years and now represents a tenth of the population. Man, like the ecosystem he lives in, is in the midst of a grand averaging.
Intermarriage has been around for a long time. Many white Britons can trace a black ancestor from the small African population that lived in England several centuries ago. About half the men of a certain Yorkshire kindred, the family Revis, share a Y-chromosome type otherwise found only in West Africa. There have been Africans in Britain since the Romans and by the eighteenth century these islands held ten thousand black people. Since then the proportion of Britons who claim recent full or partial descent from Africa has gone up by twenty times and continues to climb. The popular view of the British as a nation walled into a series of ghettos is wrong. In 1991, one electoral ward in ten (a ward is the smallest parliamentary subdivision, with around eight thousand wards in England) had more than a tenth of its citizens from an ethnic minority. Ten years later, the figure was one in eight and by 2011 will rise to one in five. The growth comes in the main not from immigration, but from the movement of people within Britain and from the simple fact that young people, many of them migrants, have more children than do old.
All geneticists are firm believers in the healing power of lust; in the ability of desire to overcome social or geographic barriers. In 2001, about one British marriage in fifty - a quarter of a million in total, with many more couples cohabiting - was between partners from different ethnic groups. Hundreds of thousands of children have one parent from Britain and the other from the Caribbean and almost as many are the progeny of white and Asian parents. British Afro-Caribbean males are half again as likely to marry a white female than are black women to find a white husband, but for the Chinese those preferences are reversed. Such relationships are not, as often believed, found just among the poor for more than half of those involved live in the suburbs and are richer and more educated than average.
Assimilation is well under way in modern Britain, among the most sexually open nations in the world. In today’s England, mate choice is made as much by level of education as by skin colour. Many other countries too, whether they like it or not, have opened up their gene pools. Homo sapiens - already the most tedious of all mammals in its geography - will soon, like the worms and the insects, be even more uniform than it was.
In that great global coalescence, Homo sapiens has evolved in just the same way as have other weeds. In other ways, man is quite unique: for he is the only animal that has escaped - or almost so - from the reach of evolution’s pitiless laws of life and death. Natural selection has long been at work on our species, even if our ingenuity has mitigated its power, with far less response in our own line than in that of the chimpanzee. Now, in the nation in which the idea was invented - and, more and more, in the world as a whole - the process has slowed down and may soon stop.
I depress my first-year students with the statement that two out of three of them will die for reasons connected to the genes they carry (a vague claim, but good enough for undergraduates). Then I try to cheer them up by pointing out that had I given the lecture in Shakespeare’s time, two out of three of them would, at the age of eighteen or so, be dead already. Even in the year of Darwin’s birth, about half of all British newborns died before they reached their majority. Life in these islands has seen a real change for the better. An English baby born in the year of the millennium had a 99 per cent chance of surviving until 2021 and that figure continues to improve. Japan does even better, and the United States rather worse, but most of the developed world has seen a revolution in the prospects of the young. In most countries, even those as poor as Ecuador, the death rate of children is less than, or no more than twice as high as, the British figure. Africa is, alas, a real exception. The death rate for under-fives is one in four in Sierra Leone and is almost as high in Angola and Liberia, while Swaziland has an overall life expectancy of just forty years, half that of Japan. As a result, differences in childhood mortality still account for most of the globe’s variation in life expectancy but, outside the continent where Homo sapiens began, those differences have withered away.
Natural selection is very interested in the death of young people, for they have not yet passed on their genes. It cares far less about the fate of the old - those over forty or so - for
their sexual lives are over and their relevance to evolution at an end. As a result, the great agent of change has lost a good part of its fuel. For most of history, the Grim Reaper was the master of man’s biological fate. Now, he is taking a rest, and inherited differences in the ability to withstand cold, starvation, vitamin deficiency or disease no longer do much to power the evolutionary machine. Plenty of people still die for those reasons, but they do so when they are elderly and evolution no longer notices them.
The Darwinian examination has two parts. In the developed world, most people pass the first paper: they stay alive until they are old enough to have children. The second section is just as inexorable but has a wider range of marks, for any candidate for evolutionary success has to find a mate and reproduce. The more children they have, the better the prospects for their genes.
Females are limited in the number of offspring they can produce by the mechanics of pregnancy and child care, while males are free to spread their sperm to a multitude of partners, even if a certain amount of persuasion is needed first. As a result, males compete for the attention of females, while females must decide which males should be allowed in. Sexual selection depends on the same logic as selection on the ability to survive: on inherited differences, not in the chances of life or death, but in the number of young. The rule applies to humans just as it does to birds and flowers.
Both humans and peacocks have more variation in male sexual success than in female. Until not long ago, many societies contained a few satisfied libertines, outnumbered by a huge mass of frustrated men. The powerful have always taken their amatory chances when they arise. Henry VIII was a minor player in the marital stakes. The emperor in the Ch’I dynasty of China maintained a palace with several thousand women available for his amusement, while in tribal societies men with high status still have many more mates than do their humble (and often celibate) fellows. Mohammed bin Laden, father of Osama of that ilk, had twenty-two wives and fifty-three children (and in the year of Osama’s birth he had six). His best known son had, last time they were counted, five wives and twenty-two children. Given the equal numbers of men and women at birth, plenty of his henchmen will be obliged to die, naturally or otherwise, without issue.
The British Isles have a history of sexual inequality that makes even the antics of the founder of the Church of England look feeble. The evidence is in the Y chromosome, which marks male descent. It comes in a diversity of forms. In the majority of places most men have their own more or less unique model of their most masculine attribute. A fifth of the men of north-west Ireland, in contrast, share a more or less identical version of the Y chromosome - which means that they all trace ancestry from the same male.
In the glorious days of old Erin, sexual inequality was rife. Lord Turlough O’Donnell, who died in 1423, had eighteen sons and fifty-nine grandsons. He was himself a descendant of the High Kings of Ireland, all of whom claimed a certain fifth-century warlord, Niall of the Nine Hostages, a man who once kidnapped St Patrick, as their common ancestor. The Y chromosome of Niall the hostage-taker has, thanks to his own exploits and those of his powerful male descendants, spread to thousands of today’s Irishmen. The surnames fit, too, for men of the Gallagher, O’Reilly and Quinn families, all of whom claim descent from the High Kings, are most likely to bear the special Y chromosome. In Ireland, for many centuries, the mightiest male passed on his genes, and many of his fellows passed their days in glum celibacy and the demand for soldiers or priests occupied their energies instead.
Today’s reproductive universe is quite different. Everywhere, the weak and the powerful - the poor and the rich - are sexually closer than they were. For every class in society, the average number of children has, thanks to technology, gone down. Natural selection cares naught for that, for the important figure is not the number of progeny, but the variation in how many children people have. That figure has shrunk. Five centuries ago in Florence, the upper crust had twice as many offspring as did the peasantry but now the Florentine poor have more than the rich and Britain is much the same (which worries the Daily Mail). The gulf has closed through restraint by the affluent rather than excess by the poor. A furtive exchange of information about birth control meant that rich families soon became smaller while those of the poor declined more slowly. Schools, too, are a powerful contraceptive. Everywhere, people with degrees have fewer children than those who drop out. As education spreads, the fertility imbalances will become smaller yet.
Inequality, in survival or in sex, is an ore refined by natural selection to adapt existence to changing conditions. The differences in people’s ability to stay alive and to have children can be combined in a single measure that shows just how much of that raw material is still available. Across the world the figure - the ‘opportunity for selection’ - is in steep decline. India tells the tale within a single country. The nation encompasses a range of cultures from tribal hill-peoples to affluent urbanites, together with vast numbers of peasant farmers whose lives are rather like those of Europeans a few centuries ago. The figures of life, death and birth when put together show that natural selection has lost nine-tenths of its power in India’s middle class when compared with the people of the tribes. The same is true when we compare the modern world with that of the Middle Ages and - to a lesser degree - even with that of the Victorians.
As Charles Darwin himself insisted, evolution is not a predictive science. Natural selection has no inbuilt tendency to improve matters (or, for that matter, to make them worse). For Homo sapiens, some nasty surprises no doubt lurk around the corner. Some day, evolution will take its revenge and we may fail in the struggle for existence against ourselves, the biggest ecological challenge of all.
Whatever the future holds, the bicentennial of his birth marks a new era in the biology of our planet. The changes are not limited to the rain forest, or the coral reefs, or the teeming tropics, but are hard at work on Darwin’s own island and on the people who live there. From Shrewsbury to the Galapagos and from worms to barnacles to human beings, there has been a triumph of the average. The Earth is, as a result, a far less interesting place than it was when HMS Beagle set sail. Whether it becomes even less so - and whether it survives at all - depends on the talents of the only creature ever to step beyond the limits of Darwinian evolution.