Mutants: On Genetic Variety and the Human Body

PROLOGUE

This book is about the making of the human body. It is about the devices that enable a single cell buried in the obscure recesses of the womb to develop into an embryo, a foetus, an infant and finally an adult. It provides an answer provisional and incomplete, yet clear in outline, to the question: how do we come to be?

In part the answer to this question is readily apparent. Our bodies – I hesitate to add our minds – are the products of our genes. At least our genes contain the information, the instruction manual, that allows the cells of an embryo to make the various parts of our bodies. But this answer, so easily given, conceals a world about which we know very little. Genetics, to quote one popular writer on the subject, is a language. ‘It has a vocabulary – the genes themselves – a grammar, the way in which the inherited information is arranged, and a literature, the thousands of instructions needed to make a human being.’ Just so. What he failed to add is that the language of the genes is largely unintelligible.

On 15 February 2001, an international consortium of scientists reported the complete, or nearly complete, sequence of the human genome. We have, we were told, some thirty thousand genes. There it was, arrayed before us, the instruction manual for making a human. Anyone may read this manual – it is freely available on the Web. But it is hardly worth the bother. The average Englishman may as well attempt the Analects of Confucius in the original for all the wisdom that it imparts. Even geneticists find most of its contents baffling. When they scan the genome they find, here and there, words whose meanings are clear enough. The meaning of others can be guessed at, perhaps because they are cognates of more familiar ones. Some of the grammar, the syntactical rules by which genes combine to give their utterances meaning, is understood as well. But the syntax of genes is vastly more complex, more subtle and nuanced, than that of any language spoken by man. And though its literature is not exactly a closed book, it is one we have scarcely begun to read.

It is not that we do not know how to decipher the genome. This book is full of experiments that attempt to do just that. Such experiments usually entail engineering embryos – either by surgically adding or removing organs, or else by adding or removing genes. Of course, the embryos always belong to animals: newts, frogs, chickens and mice. They tell us a great deal about ourselves since, as it happens, the genetic grammars of all creatures are quite similar. But just as, over time, the vocabulary and grammatical rules of human languages diverge from one another in ways large and small, so too do the languages of genes. To learn from animals alone is to run the risk of an error rather like that made by Leonardo da Vinci when he sketched a human foetus attached to what is clearly the placenta of a cow. We need, ultimately, some direct way into the human genome and into the human body. Cleopatra, one source alleges, ordered the dissection of pregnant slave girls so that she could observe the progress of their embryos. While we may admire her curiosity and ability to fit laboratory work into a busy social schedule, we can hardly follow her lead. We must approach the human body more circumspectly. We must find mutants.