Bacon’s recommendation that ‘monsters and prodigious products’ should be collected would not have startled any of his contemporaries. Princes such as Rudolf II and Frederick II of Austria had been assembling collections of marvels since the mid-1500s. Naturalists were at it too: Ulisse Aldrovandi had assembled no fewer than eighteen thousand specimens in his musem at Bologna. Bacon’s proposal that the causes of oddities should be investigated was equally conventional. The depth of his thinking is, however, apparent when he turns to why we should concern ourselves with the causes of deformity. Bacon is not merely a physician with a physician’s narrow interests. He is a philosopher with a philosopher’s desire to know the nature of things. The critical passage is trenchant and lucid. We should, he says, study deviant instances ‘For once a nature has been observed in its variations, and the reason for it has been made clear, it will be an easy matter to bring that nature by art to the point it reached by chance.’ Centuries ahead of his time Bacon recognised that the pursuit of the causes of error is not an end in itself, but rather just a means. The monstrous, the strange, the deviant, or merely the different, he is saying, reveal the laws of nature. And once we know those laws, we can reconstruct the world as we wish.
In a sense this book is an interim report on Bacon’s project. It is not only about the human body as we might wish it to be, but as it is – replete with variety and error. Some of these varieties are the commonplace differences that give each of us our unique combinations of features and, as such, are a source of delight. Others are mere inconveniences that occupy the inter-tidal between the normal and the pathological. Yet others are the result of frank errors of development, that impair, sometimes grievously, the lives of those who have them, or simply kill them in early infancy. At the most extreme are deformities so acute that it is hardly possible to recognise those who bear them as being human at all.
Bacon’s recommendation, that we should collect what he called ‘prodigious births’, may seem distasteful. Our ostensible, often ostentatious, love of human diversity tends to run dry when diversity shades into deformity. To seek out, look at, much less speak about deformity brings us uncomfortably close to naive, gaping wonder (or, to put it less charitably, prurience), callous derision, or at best a taste for thoughtless acquisition. It suggests the menageries of princes, the circuses of P.T. Barnum, Tod Browning’s film Freaks (1932), or simply the basements of museums in which exhibits designed for our forebears’ apparently coarser sensibilities now languish.
Yet the activity must not be confused with its objective. What were to Bacon ‘monsters’ and ‘prodigious births’ are to us just part of the spectrum of human form. In the last twenty years this spectrum has been sampled and studied as never before. Throughout the world, people with physiologies or physiognomies that are in some way or other unusual have been catalogued, photographed and pedigreed. They have been found in Botswana and Brazil, Baltimore and Berlin. Blood has been tapped from their veins and sent to laboratories for analysis. Their biographies, anonymous and reduced to the biological facts, fill scientific journals. They are, though they scarcely know it, the raw material for a vast biomedical enterprise, perhaps the greatest of our age, one in which tens of thousands of scientists are collectively engaged, and which has as its objective nothing less than the elucidation of the laws that make the human body.
Most of these people have mutations – that is, deficiencies in particular genes. Mutations arise from errors made by the machinery that copies or repairs DNA. At the time of writing mutations that cause some of us to look, feel, or behave differently from almost everyone else have been found in more than a thousand genes. Some of these mutations delete or add entire stretches of chromosome. Others affect only a single nucleotide, a single building block of DNA. The physical nature and extent of the mutation is not, however, as important as its consequences. Inherited disorders are caused by mutations that alter the gene’s DNA sequence so that the protein it encodes takes a different, usually defective form, or simply isn’t produced at all. Mutations alter the meaning of the genes.
Changing the meaning of a single gene can have extraordinarily far-flung effects on the genetic grammar of the body. There is a mutation that gives you red hair and also makes you fat. Another causes partial albinism, deafness, and fatal constipation. Yet another gives you short fingers and toes, and malformed genitals. In altering the meanings of genes, mutations give us a hint of what those genes meant to the body in the first place. They are collectively a Rosetta Stone that enables us to translate the hidden meanings of genes; they are virtual scalpels that slice through the genetic grammar and lay its logic bare.
Interpreting the meaning of mutations requires the adoption of a reverse logic that is, at first, counter-intuitive. If a mutation causes a child to be born with no arms, then, although it is tempting to speak of a gene for ‘armlessness’, such a mutation is really evidence for a gene that helps ensure that most of us do have arms. This is because most mutations destroy meaning. In the idiolect of genetics, they are ‘loss-of-function’ mutations. A minority of mutations add meaning and are called ‘gain-of-function’. When interpreting the meaning of a mutation it is important to know which of these you are dealing with. One way to tell is by seeing how they are inherited. Loss-of-function mutations tend to be recessive: they will only affect a child’s body when it inherits defective copies of the gene from both its parents. Gain-of-function mutations tend to be dominant: a child need have only one copy of the gene in order to see its effects. This is not an invariable distinction (some dominantly inherited mutations are loss-of-function) but it is a good initial guide. Gain or loss, both kinds of mutations reveal something about the function of the genes that they affect, and in doing so, reveal a small part of the genetic grammar. Mutations reverse-engineer the body.
Who, then, are the mutants? To say that the sequence of a particular gene shows a ‘mutation’, or to call the person who bears such a gene a ‘mutant’, is to make an invidious distinction. It is to imply, at the least, deviation from some ideal of perfection. Yet humans differ from each other in very many ways, and those differences are, at least in part, inherited. Who among us has the genome of genomes, the one by which all other genomes will be judged?
The short answer is that no one does. Certainly the human genome, the one whose sequence was published in Nature on 15 February 2001, is not a standard; it is merely a composite of the genomes of an unknown number of unknown people. As such, it has no special claim to normality or perfection (nor did the scientists who promoted and executed this great enterprise ever claim as much for it). This arbitrariness does not diminish in the slightest degree the value of this genomic sequence; after all, the genomes of any two people are 99.9 per cent identical, so anyone’s sequence reveals almost everything about everyone’s. On the other hand, a genome nearly three thousand million base-pairs long implies a few million base-pairs that differ between any two people; and it is in those differences that the interest lies.