beings speak the same genetic language.
Pharaoh Psamtik the First, who flourished in the seventh century before Christ, searched for the first word of all. He put a baby in the care of a dumb nurse and noted the sounds it made. One word was (or seemed to be) ‘becos’, the Phrygian for bread, suggesting to Psamtik that the Phrygians (who lived in what is modern Turkey) were the first people of all. A computer search through the millions of DNA letters now sequenced from dozens of organisms also hints at a shared structure from bacteria to humans; the father (or mother) of all genes, that might have persisted since life began. The scientist who published the ur-sequence has turned the information to a useful end. Assigning musical notes to each DNA letter he used them as a theme for a ‘symphony of life’.
Gene sharing, from bacteria to humans, proves the unity of existence. It also defines the limits of what biology can say. A chimp may share ninety-eight per cent of its DNA with ourselves but it is not ninety-eight per cent human: it is not human at all – it is a chimp. And does the fact that we have genes in common with a mouse, or a banana, say anything about human nature? Some claim that genes will tell us what we really are. The idea is absurd.
One gene is found in a certain form in men, but a different one in all other apes. It codes for a molecule on the cell surface much involved in communication between cells, brain cells more than most. Perhaps this is the gene – or one of the genes – that makes us human. Its message spelt out in the four DNA letters, A, G, C and T starts like this: AACCGGCAGACAT … Altogether, it has three thousand letters. Together they contain an important part of the tedious biological story of being a man or woman rather than a chimpanzee or gorilla. Needless to say, that ancestral bulletin does nothing to tell us – or apes – what it means to be part of humankind. That calls for a lot more than a sequence of DNA bases and lies outside the realm of science altogether.
St Bede – whose writings are the best source of information about England before the eighth century – had a powerful metaphor for existence. To him human existence was ‘As if when on a winter’s night you sit feasting with your ealdormen and thegns, a single sparrow should fly swiftly into the hall, and coming in at one door instantly fly out through another. In that time in which it is indoors it is indeed not touched by the fury of the winter, but yet, this smallest space of calmness being passed almost in a flash, from winter going into winter again, it is lost to your eyes. Somewhat like this appears the life of man; but of what follows or what went before, we are utterly ignorant.’
His allegory was a religious one but has a biological parallel. Genes have a memory of their own. To read it gives new hope of looking beyond the hall into which our own brief existence is confined. It allows us to learn what went before in the life of our own species; to guess at what happened much earlier, and even to speculate about what fate may hold for generations yet to come.
Chapter Two THE RULES OF THE GAME
It is always painful to watch an unfamiliar game and to try to work out what is going on. Although I lived in the United States for several years, and although the sport is now shown on British television, I have almost no idea how American football works. There is a clear general desire to score, but how play stops and starts and why the spectators cheer at odd moments remains a closed book. A deep lack of interest in ball games helps in my case, but cricket is equally dull to sporting enthusiasts from other countries. They just do not understand the rules.
The rules of the game known as sexual reproduction are not obvious from its results. As a consequence, how inheritance works was a closed book until quite recently. Part of the problem is that the way sex works is so different from how it seems that it ought to. It seems obvious that a character acquired by a parent must be passed on to the next generation. After all, blacksmiths’ children tend to be muscular and those of criminals less than honest. In the Bible, Jacob, when allowed to choose striped kids from Laban’s herd of goats, put striped sticks near the parents as they mated in the hope of increasing the number available. Later, pregnant women looked on pictures of saints and avoided people with deformities. It took a series of painful trials in which generations of mice were deprived of their tails to show that acquired characters were not in fact inherited. Of course, Jews had been doing the same experiment for thousands of years.
Another potent myth about inheritance is that the characters of a mother and a father pass to their blood, which is mixed in their offspring. Children are, as a result, a blend of the attributes of their parents. This idea – a sort of genetics of the average – copes quite well with traits such as height or weight but fails to explain why a child may look like a distant relative rather than its father or mother. The idea lasted until just a few years ago. The stud book is the record kept by racehorse breeders. A mare who had borne a foal by mating with a non-stud stallion was struck off as her blood was deemed to be polluted. Indeed, a survey of elderly women in Bristol showed that half believed in the chance of a woman having a black baby if she had sex with a black man many years before. The crones of the west country, like the breeders of horses, had never managed to work out the instructions for the reproductive game.
The only section of The Origin of Species which does not make good reading today is Chapter Five, ‘Laws of Variation’. Darwin got it wrong and, after much agonising, suggested that the organs of parents passed material to the blood and then to sperm and egg. Children were, he thought, intermediate between those who produced them. Such a mode of inheritance would be fatal to the idea of evolution. The problem was pointed out by Fleeming Jenkin, the first Professor of Engineering at the University of Edinburgh. Writing in 1867 – and with a sturdy disregard of today’s proprieties – Jenkin imagined ‘a white man wrecked on an island inhabited by negroes. Suppose him to possess the physical strength, energy and ability of a dominant white race. There does not follow the conclusion that after a … number of generations the inhabitants of the island will be white. Our shipwrecked hero would probably become king; … he would have a great many wives, and children … much superior in average intelligence to the negroes, but can anyone believe that the whole island will gradually acquire a white or even a yellow population? A highly favoured white cannot blanch a nation of negroes.’
Jenkin saw that the attributes of a distant ancestor, valuable as they might be, are of little help to later generations if bloods mix. Characters would then blend over the years until their effects disappear. However useful an ink drop in a gallon of water might be at some time in the future it is impossible to get it back from a single mixed drop. Genetics by blending means that any advantageous character would be diluted out in the next generation. Fortunately, the blood myth is wrong.
It was shot down by Galton himself. He transfused blood from a black rabbit to a white to see if the latter had black offspring. It did not. Inheritance by dilution had been disproved, but Galton had nothing to put in its place.
Unknown to either Darwin or to his cousin the rules of genetics had already been worked out by another biological genius. Gregor Mendel lived in Bohemia and published in a rather obscure scientific journal, the Transactions of the Brunn Natural History Society. His breakthrough was overlooked for thirty-five years after it was published in 1866. Mendel, an Augustinian monk, attempted a science degree but failed to complete it. Like Darwin and Galton he suffered from bouts of depression which prevented him from working for months at a time. Nevertheless, he persisted with his experiments. He found that the inherited message is transmitted according to a simple set of regulations – the grammar of the genes. Later in his career (and setting a precedent for the present age) he was unable to continue with research because of the pressures of administration. The study of inheritance came to a halt for almost half a century.
Grammar is always more tedious than vocabulary, but cannot be avoided. The rest of this chapter explores the basic rules of genetics. Those who teach the subject still have an obsession with Mendel and his peas and I make no excuse for having them as a first course.
Mendel made a conceptual breakthrough. Instead of (like his predecessors) working on traits such as height or weight (which could only be measured) Mendel was more or less the first biologist to count anything. This put him on the road to his great