Kitabı oku: «The Language of the Genes»

Introduction THE FINGERPRINTS OF HISTORY

In 1902, in Paris, a horrible murder was solved by the great French detective Alfonse Bertillon. He used a piece of new technology which struck fear into the heart of the criminal community. Eight decades later two young girls were killed near the Leicestershire village of Narborough. Again, the murderer was found through a technical advance, although the machinery involved would have been beyond the comprehension of Bertillon. These events link the birth and the coming-of-age of human genetics.

The Parisian killer was trapped because he left a fingerprint at the scene of the crime. For the first time, this was used in evidence as a statement of identity. The idea came from ancient Japan, where a finger pressed into a clay pot identified its maker. The Leicestershire murderer was caught in the same way. A new test looked for individual differences in genetic material. This ‘DNA fingerprint’ was as much a statement of personal uniqueness as Bertillon’s clue or the potter’s mark. As usual, life was more complex than science. The killer, a baker called Colin Pitchfork, was caught only after DNA fingerprints had eliminated a young man who had made a false confession and after Pitchfork had persuaded a friend to give a fraudulent blood sample under his name.

The idea that fingerprints could be used to trace criminals came from Charles Darwin’s cousin, Francis Galton. He founded the laboratory in which I work at University College London, the first human genetics institute in the world. Every day I walk past a collection of relics of his life. They include some rows of seeds that show similarities between parents and offspring, an old copy of The Times and a brass counting gadget that can be hidden in the palm of the hand. Each is a reminder of Galton. As well as his revolution in detective work Galton was the first person to publish a weather map and the only one to have made a beauty map of Britain, based on a secret ranking of the local women on a scale of one to five (the low point, incidentally, being in Aberdeen).

His biography reveals an unrelieved eccentricity, well illustrated by the titles of a dozen of his three hundred scientific papers: On spectacles for divers; Statistical inquiries into the efficacy of prayer; Nuts and men; The average flush of excitement; Visions of sane persons; Pedigree moths; Arithmetic by smell; Three generations of lunatic cats; Strawberry cure for gout; Cutting a round cake on scientific principles; Good and bad temper in English families; and The relative sensitivity of men and women at the nape of the neck. Galton travelled much in Africa, regarding the natives with some contempt and measuring the buttocks of the women using a sextant and the principles of surveying.

Galton’s work led, indirectly, to today’s explosion in human genetics. His particular interest was in the inheritance of genius (a class within which he placed himself). In his 1869 book Hereditary Genius, he investigated the ancestry of distinguished people and found a tendency for talent to crop up again and again in the same family. This, he suggested, showed that ability was inborn and not acquired. Hereditary Genius marked the first attempt to establish patterns of human inheritance with well-defined traits – such as becoming (or failing to become) a judge rather than with mere speculation about vague qualities such as fecklessness.

Galton and his followers would be astonished at what biology can now do. It still does not understand attributes such as genius (and reputable scientists hardly concern themselves with them), but DNA is much involved in mental and physical illness. Half a million DNA samples have been taken by police in Britain since the test was invented, and the government has a scheme to follow the genes – and the ailments – of the same number of its citizens over two decades in the hope of finding the biological errors responsible for killers like cancer and heart disease. New tests mean that parents can sometimes choose whether to risk the birth of a child with an inborn defect. Ten thousand such illnesses are known and if we include, as we should, all ailments with an inherited component, most people die because of the genes they carry.

Genetics does more than reveal fate. Humans share much of their heritage with other creatures. As Galton himself illustrated with the appropriate impression pasted near that made by Gladstone, the prime minister, chimpanzees have fingerprints. Now we know that much of their DNA is identical to our own (as indeed is that of bananas). All this suggests that humans and apes are close relatives.

Genetics is the key to the past. As every gene must have an ancestor, inherited diversity can be used to piece together a picture of history more complete than from any other source. Each segment of DNA is a message from our forebears and together they contain the whole story of human evolution. Everyone alive today is a living fossil and carries within themselves a record that revisits the birth of humankind. The Origin of Species expresses the hope that ‘light will be thrown on the origin of man and his history’. Darwin’s hint that humans share a common descent with all other creatures is now accepted by all scientists, because of the evidence of the genes.

Evolution, the appearance of new forms by the alteration of those already present, is no more than descent with modification. The same is true of language. As a boy, I was amused by the tale of the order going down the line of command to soldiers in the trenches. ‘Send reinforcements, we’re going to advance’ changed to ‘Send three and fourpence, we’re going to a dance’ as it passed from man to man. This simple tale illustrates how accidents, as an inherited message is copied, can lead to change. Because of mutation, life, too, is garbled during transmission.

This book is about inheritance: about the clues of our past, present and future that we all contain. The language of the genes has a simple alphabet, with not twenty-six letters, but four; the DNA bases – adenine, guanine, cytosine and thymine (A, G, C and T for short). They are arranged in words of three letters such as CGA or TGG. Most code for different amino acids, which are themselves joined together to make proteins, the building blocks of the body.

The economy of life’s language can be illustrated with an odd quotation from a book called Gadsby, written in 1939 by one Ernest Wright: ‘I am going to show you how a bunch of bright young folks did find a champion, a man with boys and girls of his own, a man of so dominating and happy individuality that youth was drawn to him as a fly to a sugar bowl.’ This sounds somewhat peculiar, as does the rest of the fifty-thousand word book, and it is. The quotation, and the whole work, lacks the letter ‘e’. An English sentence can be written with twenty-five letters instead of twenty-six, but only just. Biology manages with a mere four.

Although its vocabulary is simple the genetical message is very long. Each cell in the body contains about six feet of DNA. There are so many cells that if all the DNA in a single human body were stretched out it would reach to the moon and back eight thousand times. Twenty years ago, the Human Genome Project set out to read the whole of its three thousand million letters, and to publish perhaps the most dreary volume ever written, the equivalent of a dozen or so copies of the Encyclopaedia Britannica. The task is now more or less complete. The sequencers followed a grand scientific tradition: the Admiralty, after all, sent the Beagle to South America with Darwin on board not because they were interested in evolution but because they knew that if they were to understand (and, with luck, control) the world, the first step was to map it. The chart of the genes, like that of the Americas, has been expensive to make; but – like the theory of evolution itself – it may change our perception of ourselves.

Powerful ideas like inheritance and evolution soon attract myths. Impressed by his studies of genius, Galton founded the science (if that is the right word) of eugenics. Its main aim was ‘to check the birth rate of the Unfit and improve the race by furthering the productivity of the fit by early marriage of the best stock’. He led the new field of human genetics into a blind alley from which it did not emerge for half a century. At his death, he left £45,000 to found the Laboratory of National Eugenics at University College London and, in fine Victorian tradition, £200 to his servant who had worked for him for forty years. His research institute soon changed its name to the Galton Laboratory to escape from the eugenical taint. What became of his servant is not recorded.

Galton’s social ideas and Darwin’s evolutionary insights had a pervasive effect on the intellectual history of the twentieth century. They influenced left and right, liberal and reactionary, and continue – explicitly or otherwise – to do so. Many disparate figures trace their ideas to The Origin and to Hereditary Genius. All are united by one belief: in biology as destiny, in the power of genes over those who bear them.

The most famous monument in Highgate Cemetery in London, a couple of miles north of today’s Galton Laboratory, is that of Karl Marx. Its inscription is well known: ‘Philosophers have only interpreted the world. The point, however, is to change it.’ Darwinism was soon used in an attempt to live up to that demand. The philosopher Herbert Spencer, buried just across the path from Marx, founded what he called Social Darwinism; the notion that poverty and wealth are inevitable as they reflect the biological rules that govern society. In his day, Spencer was famous. His Times obituary claimed that ‘England has lost the most widely celebrated and influential of her sons.’ Now he is remembered only for that neatly circular phrase ‘the survival of the fittest’ and for inventing the word ‘evolution’.

He wrote with a true philosopher’s clarity: ‘Evolution is an integration of matter and concomitant dissipation of motion; during which matter passes from an indefinite, incoherent homogeneity, to a definite, coherent heterogeneity, through continuous differentiations and integrations’. Those lucid lines were parodied by a mathematical contemporary: ‘A change from a nohowish, untalkaboutable all-alikeness to a somehowish and in general talkaboutable not-all-alikeness by continuous somethingelsifications and sticktogetherations.’

Spencer used The Origin of Species as a rationale for the excesses of capitalism. The steel magnate Andrew Carnegie was one of many to be impressed by the idea that evolution excuses injustice. He invited Herbert Spencer to Pittsburgh. Unfortunately, the philosopher’s response to his trip to see his theories worked out in steel and concrete was that ‘Six months’ residence here would justify suicide.’

Galton, too, supported the idea of breeding from the best and sterilising those whose inheritance did not meet with his approval. The eugenics movement joined a gentle concern for the unborn with a brutal rejection of the rights of the living (a combination not unknown today). Galton’s main interest in genetics was as a means to forestall the imminent decline of the human race. He claimed that families of ‘genius’ had fewer children than most and was concerned about what this meant for the future. It was man’s duty to interfere with his own evolution. As he said: ‘What Nature does blindly and ruthlessly, man may do providently, quickly and kindly.’ Perhaps his own childless state helped to explain his anxiety.

Many of the eugenicists shared the highly heritable attributes of wealth, education and social position. Francis Galton gained his affluence from his family of Quaker gunmakers. Much of his agenda was the survival of the richest. Other eugenicists were on the left. They felt that if economies could be planned, so could genes. George Bernard Shaw, at a meeting attended by Galton in his last years, claimed that ‘Men and women select their wives and husbands far less carefully than they select their cashiers and cooks.’ Later, he wrote that ‘Extermination must be put on a scientific basis if it is ever to be carried out humanely and apologetically as well as thoroughly.’ Shaw was, no doubt, playing his role as Bad Boy to the Gentry, but subsequent events made his tomfoolery seem even less droll than it did at the time.

Sometimes, such notions were put into practice. Paraguay has an isolated village with an unusual name: Nueva Germania, New Germany. Many of its inhabitants have blonde hair and blue eyes. Their names are not Spanish, but are more likely to be Schutte or Neumann. They are the descendants of an experiment; an attempt to improve humankind. Their ancestors were chosen from the people of Saxony in 1886 by Elisabeth Nietzsche – sister of the philosopher, who himself uttered the immortal phrase ‘What in the world has caused more damage than the follies of the compassionate?’ – as particularly splendid specimens, selected for the purity of their blood. The idea was suggested by Wagner (who once planned to visit). The New Germans were expected to found a community so favoured in its genetic endowment that it would be the seed of a new race of supermen. Elisabeth Nietzsche died in 1935 and Hitler himself wept at her funeral. Today the people of Nueva Germania are poor, inbred and diseased. Their Utopia has failed.

The eugenics movement had an influence elsewhere in the New World. In 1898, Charles Davenport, then professor of evolutionary biology at Harvard, was appointed as Director of the Cold Spring Harbor Laboratory on Long Island Sound. Initially, the Laboratory concentrated on the study of ‘the normal variation of the animals in the harbor, lakes and woods, and the production of abnormalities’. It carried out some of the most important work in early twentieth-century biology.

Soon, Mrs E H Harriman, widow of the railway millionaire, decided to devote part of her fortune to the study of human improvement. The Eugenics Record Office was built next to the original laboratory. It employed two hundred field workers, who were sent out to collect pedigrees. Their 750,000 genetic records included studies of inherited disease and of colour blindness; but also recorded the inheritance of shyness, pauperism, nomadism, and moral control.

Davenport’s work had an important effect on American society. The first years of the twentieth century saw eugenical clubs with prizes for the fittest families and, for the first time, medicine became concerned about whether its duty to the future outweighed the interests of some of those alive today. In Galtonian style, Davenport claimed that: ‘Society must protect itself; as it claims the right to deprive the murderer of his life so also may it annihilate the hideous serpent of hopelessly vicious protoplasm.’ Twenty-five thousand Americans were sterilised because they might pass feeble-mindedness or criminality to future generations. One judge compared sterilisation with vaccination. The common good, he said, overrode individual rights.

Another political leader had similar views. ‘The unnatural and increasingly rapid growth of the feeble-minded and insane classes, coupled as it is with steady restriction among all the thrifty, energetic and superior stocks constitutes a national and race danger which it is impossible to exaggerate. I feel that the source from which the stream of madness is fed should be cut off and sealed off before another year has passed.’ Such were the words of Winston Churchill when Home Secretary in 1910. His beliefs were seen as so inflammatory by later British governments that they were not made public until 1992.

One of Galton’s followers was the German embryologist Ernst Haeckel. Haeckel was a keen supporter of evolution. He came up with the idea (which later influenced Freud) that every animal re-lived its evolutionary past during its embryonic development. His interest in Galton and Darwin and his belief in inheritance as fate led him to found the Monist League, which had thousands of members before the First World War. It argued for the application of biological rules to society and for the survival of some races – those with the finest heritage – at the expense of others. Haeckel claimed social rules were the natural laws of heredity and adaptation. The evolutionary destiny of the Germans was to overcome inferior peoples: ‘The Germans have deviated furthest from the common form of ape-like men … The lower races are psychologically nearer to the animals than to civilized Europeans. We must, therefore, assign a totally different value to their lives.’

In 1900 the arms manufacturer Krupp offered a large prize for the best essay on ‘What can the Theory of Evolution tell us about Domestic Political Development and the Legislation of the State?’ There were sixty entries. In spite of the interests of capital, the first German eugenic sterilisation was carried out by a socialist doctor (albeit one who claimed that trade union leaders were more likely to be blond than were their followers).

While imprisoned after the Beer Hall Putsch, Hitler read the standard German text on human genetics, The Principles of Human Heredity and Race Hygiene, by Eugene Fischer. Fischer was the director of the Berlin Institute for Anthropology, Human Heredity and Eugenics. One of his assistants, Joseph Mengele, later achieved a certain notoriety for his attempts to put Galtonian ideas into practice. Fischer’s book contained a chilling phrase: ‘The question of the quality of our hereditary endowment’ – it said – ‘is a hundred times more important than the dispute over capitalism or socialism.’

His thoughts were echoed in Mein Kampf: ‘Whoever is not bodily and spiritually healthy and worthy shall not have the right to pass on his suffering in the body of his children’. Hitler took this to its dreadful conclusion with the murder of those he saw as less favoured in order to breed from the best. The task was taken seriously, with four hundred thousand sterilisations of those deemed unworthy to pass on their genes, sometimes by the secret use of X-rays as the victims filled in forms. Those in charge of the programme in Hamburg estimated that one fifth of its people deserved to be treated in this way.

By 1936 the German Society for Race Hygiene had more than sixty branches and doctorates in racial science were offered at several German universities. Certain peoples were, they claimed, inferior because of inheritance. Half of those at the Wannsee Conference (which decided on the final solution of the Jewish problem) had doctorates and many justified their crimes on scientific grounds. The eugenics movement in Germany was opposed to abortion (except of the unfit) and imposed stiff penalties – up to ten years in prison – on any doctor rash enough to carry it out. The number of children born to women of approved stock went up by a fifth. The Hitlerian conjunction of extreme right wing views, an obsession with racial purity and a hatred of abortion has its echoes today.

Concern for the purity of German blood reached absurd lengths. One unfortunate member of the National Socialist Party received a transfusion from a Jew after he had been in a road accident. He was brought before a disciplinary court to see if he should he excluded from the Party. Fortunately, the donor had fought in the First World War, so that his Jewish red cells were – just about – acceptable.

The disaster of the Nazi experiment ended the eugenics movement, at least in its primitive form. Its blemished past means that human genetics is marked by the fingerprints of its own history. It sometimes seems to find them hard to wipe off. They should not be forgotten now that the subject is, for the first time, in a position to control the biological future.

Galton and his followers felt free to invent a science which accorded with their own prejudices. They believed that the duty to genes outweighs that to those who bear them. They were filled with extraordinary self-assurance and great weight was placed on their views although in retrospect it is obvious that they knew almost nothing.

Today’s new knowledge is as controversial as was the old ignorance. Even so, disputes among modern biologists are not about the vague general issues that obsessed their predecessors. Instead they concern themselves with the fate of individuals rather than of all humanity. Genetics has become a science and, as such, has narrowed its horizons.

Nevertheless, it raises ethical issues which will not go away. The newspapers are filled with debates about the morals of gene therapy or of human cloning, neither of which show any sign of becoming a reality. However, the diagnosis of defective genes before birth has already shifted the balance between birth and abortion to reduce the number of damaged children. This raises passions, from those who feel – in spite of the high natural wastage of fertilised eggs – that all foetuses are sacred, to others who consider that to pass on a faulty gene is equivalent to child abuse. Genetics presents a more universal difficulty – the problem of knowledge. Soon, it will tell many of us how and when we may die. Already, it is possible to diagnose at birth genes which will kill in childhood, youth or middle age. More will soon be found. Will people want to know that they are at risk of a disease which cannot be treated? Many genes show their effects in those who inherit damaged DNA from each parent. As everyone is likely to pass on a single copy of at least one such gene, will this help to choose a partner or to decide whether to have children?

Attitudes to inborn disease are flexible. In Ghana, babies are sometimes born with an extra finger or toe. Some tribal groups take no notice, others rejoice as it means that the new member of the family will become rich; but others, just a few miles away, regard such children with horror and they are drowned at birth. Even Christianity has seen the genetically unfortunate as less than human. Martin Luther himself declared that Siamese twins were monsters without a soul. Attitudes to genetics will always be influenced by those to abortion, which vary with time and place. St Augustine saw a foetus as part of its mother and not worthy of protection and in spite of its present views the Catholic Church did not condemn abortion until the thirteenth century. Ireland has a constitutional clause that establishes the right to life of the unborn child; while across the Irish Sea abortion until the third month is available almost on demand. Embryo research (which is becoming important with the discovery that embryonic cells can be used to treat adult disease) is forbidden in Germany but lightly controlled in Britain. All this shows how hard it is to set ethical limits to the new biology.

The problem can be illustrated with some old-fashioned biological discrimination. There has always been prejudice against certain genes, those carried on the chromosomes that determine sex. Women have two ‘X’ chromosomes, men a single X chromosome and a much smaller ‘Y’. All eggs have an X but that of sperm are of two kinds, X or Y. At fertilisation, both XY males and XX females are produced in equal number. Sex is as much a product of genes as are blood groups.

How the value of these genes is judged shows how biological choice can depend on circumstances. Sometimes, Y chromosomes seem to be worth less than Xs. When it comes to wars, murders and executions, males have always been more acceptable victims than females. But the balance can shift. Many parents express a preference for sons, especially as a first-born. Some even try to achieve them. The recipes vary from the heroic to the hopeful. In ancient Greece, to tie off the left testicle was said to do the job, while mediaeval husbands drank wine and lion’s blood before copulating under a full moon. Less drastic methods included sex in a north wind and hanging one’s underpants on the right side of the bed.

To sell gender is an easy way to make money. It has, after all, a guaranteed fifty per cent success rate. Today’s methods vary from the use of baking soda or vinegar at the appropriate moment (to take advantage of a supposed difference in the resistance of X and Y-bearing sperm to acids and alkalis) to sex at particular times of the female cycle. A diet high or low in salt is also said to help. Such recipes are useless and some of those who sell them have been prosecuted for fraud.

Now, fraud is out of date. Sex can be chosen in many ways. One is to separate X and Y sperm and to fertilise a woman with the appropriate type. The methods are not absolute, but shift the ratios by about two to one for males and four to one for females. Since Louise Brown in 1978, thousands of children have been born by in-vitro fertilisation, with sperm added to egg in a test-tube. A single cell can be taken from the embryo and its sex determined (and, indeed, as young male embryos grow faster, simply to choose the largest embryo biases the ratio of males). Only those of the desired gender are implanted into the mother. This technique has led to the birth of hundreds of babies.

Pregnancy termination is a less kind, but equally effective, way of choosing the sex of a child. Aristotle himself felt that a male foetus should be protected from abortion after forty days, but a female only after ninety. A recent survey of geneticists themselves showed that, in Holland, none would accept pregnancy termination just to choose the sex of a child, in Britain one in six, and in Russia nine out of ten. The Indian government was forced to shut down clinics which chose the sex of a baby with a test of the chromosomes of the foetus and aborted those with two Xs. More than two thousand pregnancies a year were ended for this reason in Bombay alone. The main reason was the need for large dowries when daughters were married off. The advertisements said ‘Spend six hundred rupees now, save fifty thousand later.’ The preference is an old one. A nineteenth-century visitor to Benares recorded that ‘Every female infant in the Rajah’s family born of a lawful wife, or Rani, was drowned as soon as it was born in a hole in the earth filled with milk.’ The rulers’ many wives were said to have produced no grown-up daughters for more than a century. The government nowadays pays a bonus for girl babies, but some states now have four females to five males and the country as a whole has a deficit of girls and women equivalent to the entire British female population.

All these methods interfere with genes. Their acceptability varies from the reasonably uncontentious choice of sperm to a crime where the murder of girl children is concerned. Where to draw the line depends on one’s own social, political or religious background; on how acceptable the notion might be that fate should depend on biological merit. All readers of this book would, I imagine, abhor infanticide, and most might feel that to terminate a pregnancy just because it is the wrong sex was also wrong. They might worry less about the choice of X or Y sperm.

The choice of a child’s sex can, however, involve more than parental self-indulgence. Sometimes it is a matter of life and death. Many inherited diseases are carried on the X chromosome. In most girls, an abnormal X is masked by a normal copy. Boys do not have this option, as they have but a single X. For this reason, sex-linked abnormalities, as they are known, are much more common in boys than in girls. They can be distressing. Duchenne muscular dystrophy is a wasting disease of the muscles. Symptoms can appear even in three year-olds and affected children have to wear leg braces by the age of seven, are often in a wheelchair by eleven and may die before the age of twenty-five. Parents who have seen one of their sons die of muscular dystrophy are in the agonising position of knowing that any later son has a one in two chance of having inherited it. A couple who have had a son with the illness can scarcely be blamed for a desire to ensure that no later child is affected. They hope to control the quality of their offspring and few will criticise them for doing so. Genetics has changed their ethical balance.

If a couple has a son with muscular dystrophy they know at once that the mother carries the gene. The chance of a second son with the disease is hence far greater than before. It is still just one in two, so that to terminate all male pregnancies means a real possibility of losing a normal boy. Even those who dislike the idea of choice of a child’s sex with X-bearing sperm might change their minds in these circumstances. Others would go further and accept the option of an externally fertilised embryo or the termination of all pregnancies which would produce a son.

Now, such choices have become more precise. The gene for muscular dystrophy has been found and changes in the DNA can show whether a foetus bears it. Hundreds of centres use the test. But the method is far from perfect. The gene can go wrong in many ways and not all of them show up. A foetus that appears normal may hence, in a proportion of cases, carry the gene. This complicates the parents’ decision as to whether to continue with a pregnancy. To sample foetal tissues also involves a certain hazard. This has become smaller as technology improves, with a check of foetal cells in the mother’s blood, but the risks of the test must themselves be weighed in the moral scales.

As more is found about the genes that cause death not at birth, or in the teens, but in middle or old age the dilemmas increase. Given the opportunity, some might avoid the birth of a baby doomed to dementia through Alzheimer’s disease in its forties. Others would argue that forty years of life are not to be dismissed; and that, in four decades of science, the cure may be found.

Decisions about the future of an unborn child will, as a result, more and more be influenced by estimates of risk and of quality: by whether the rights of a foetus depend on its genes. Such judgements are not just scientific decisions, but depend on the society and the people who make them. The debacle of the eugenics movement led to an understandable reluctance even to consider the idea of choices about rights based on inherited merit, but the new knowledge means that they are unavoidable.

Galton himself would have been delighted by the idea of preventing the birth of the damaged. The new eugenics can be overt. The Chinese People’s Daily is frank in its views. It reported a scheme to ban the marriage of those with mental disease unless they were sterilised with a robust simplification of Mendelism: ‘Idiots give birth to idiots!’ the eugenical message is often justified on financial grounds. At the Sesquicentennial Exhibition in Philadelphia in 1926 the American Eugenics Society had a board that counted up the $100 per second supposed to be spent on people with ‘bad heredity’. Sixty years later, one proponent of the plan to sequence the human genome claimed that the project would pay for itself by ‘curing’ schizophrenia – by which he meant the termination of pregnancies carrying the as yet hypothetical and undiscovered gene for the disease. The 1930s were a period of financial squeeze for health care. Seventy years on, the state is still anxious to limit the amount spent on medicine in the face of an inexorable rise in costs, with inborn diseases among the most expensive. There is a fresh danger that genetics will be used as an excuse to discriminate against the handicapped in order to save money.

Genetics – science as a whole – owes its success to the fact that it is reductionist: that to understand a problem, it helps to break it down into its component parts. The human genome project marks the extreme application of such a view. The approach works well in biology as far as it goes, but it only goes so far. Its limits are seen in a phrase once notorious in British politics, the late Prime Minister Mrs Thatcher’s statement that ‘There is no such thing as society, there are only individuals.’ The failures of her philosophy are all around us. To say, with Galton and his successors, ‘There are no people, there are only genes’ is to fall into the same trap.

In spite of the lessons of the past, there has been a resurgence of the dangerous and antique myth that biology can explain everything. Some have again begun to claim that we are controlled by our inheritance. They promote a kind of biological fatalism. Humanity, they say, is driven by its inheritance. The predicament of those who fail comes from their own weakness and has little to do with the rest of us. Such nouvelle Galtonism suggests that human existence is programmed and that, apart from a little selective pregnancy termination, there is no point in any attempt to change it – which is convenient for those who like things the way they are.

After the Second World War, genetics had – it seemed – at last begun to accept its own limits and to escape its confines as the haunt of the obsessed. Most of those in the field today are cautious about claims that the essence of humanity lies in DNA. Although it can say extraordinary things about ourselves, genetics is one of the few sciences that has reduced its expectations.

In mediaeval Japan, the science of dactylomancy – the interpretation of personality from fingerprints – had it that people with complex patterns were good craftsmen, those with many loops lacked perseverance, while those whose fingers carried an arched pattern were crude characters without mercy. Human genetics has escaped from its dactylomantic origins. The more we learn about inheritance the more it seems that there is to know. The shadow of eugenics has not yet disappeared but is fainter than it was. Now that genetics has matured as a subject it is beginning to reveal an extraordinary portrait of who we are, what we were, and what we may become. This book is about what that picture contains.