Genome: The Autobiography of a Species in 23 Chapters. Matt Ridley
being the last abbot to pay it. Perhaps his greatest claim to fame, he might have reflected in old age, was that he made Leos Janáček, a talented nineteen-year-old boy in the choir school, the choirmaster of Brünn.
In the garden, Mendel had been hybridising: crossing different varieties of pea plant. But this was no amateur gardener playing at science; this was a massive, systematic and carefully thought-out experiment. Mendel chose seven pairs of varieties of peas to cross. He crossed round-seeded peas with wrinkled ones; yellow cotyledons with green ones; inflated seed pods with wrinkled seed pods; grey seed coats with white seed coats; green unripe pods with yellow unripe pods; axial flowers with terminal flowers; tall stems with dwarf stems. How many more he tried we do not know; all of these not only breed true, but are due to single genes so he must have chosen them knowing already from preliminary work what result to expect. In every case, the resulting hybrids were always like just one parent. The other parent’s essence seemed to have vanished. But it had not: Mendel allowed the hybrids to self-fertilise and the essence of the missing grandparent reappeared intact in roughly one-quarter of the cases. He counted and counted – 19,959 plants in the second generation, with the dominant characters outnumbering the recessives by 14,949 to 5,010, or 2.98 to 1. It was, as Sir Ronald Fisher pointed out in the next century, too suspiciously close to a ratio of three. Mendel, remember, was good at mathematics and he knew well before the experiments were over what equation his peas were obeying.2
Like a man possessed, Mendel turned from peas to fuschias, maize and other plants. He found the same results. He knew that he had discovered something profound about heredity: characteristics do not mix. There is something hard, indivisible, quantum and particulate at the heart of inheritance. There is no mingling of fluids, no blending of blood; there is instead a temporary joining together of lots of little marbles. In retrospect, this was obvious all along. How else could people account for the fact that a family might contain a child with blue eyes and a child with brown? Darwin, who none the less based his theory on blending inheritance, hinted at the problem several times. ‘I have lately been inclined to speculate’, he wrote to Huxley in 1857, ‘very crudely and indistinctly, that propagation by true fertilisation will turn out to be a sort of mixture, and not true fusion, of two distinct individuals…I can understand on no other view the way in which crossed forms go back to so large an extent to ancestral forms.’3
Darwin was not a little nervous on the subject. He had recently come under attack from a fierce Scottish professor of engineering, strangely named Fleeming Jenkin, who had pointed out the simple and unassailable fact that natural selection and blending inheritance did not mix. If heredity consisted of blended fluids, then Darwin’s theory probably would not work, because each new and advantageous change would be lost in the general dilution of descent. Jenkin illustrated his point with the story of a white man attempting to convert an island of black people to whiteness merely by breeding with them. His white blood would soon be diluted to insignificance. In his heart Darwin knew Jenkin was right, and even the usually ferocious Thomas Henry Huxley was silenced by Jenkin’s argument, but Darwin also knew that his own theory was right. He could not square the two. If only he had read Mendel.
Many things are obvious in retrospect, but still take a flash of genius to become plain. Mendel’s achievement was to reveal that the only reason most inheritance seems to be a blend is because it involves more than one particle. In the early nineteenth century John Dalton had proved that water was actually made up of billions of hard, irreducible little things called atoms and had defeated the rival continuity theorists. So now Mendel had proved the atomic theory of biology. The atoms of biology might have been called all sorts of things: among the names used in the first years of this century were factor, gemmule, plastidule, pangene, biophor, id and idant. But it was ‘gene’ that stuck.
For four years, starting in 1866, Mendel sent his papers and his ideas to Karl-Wilhelm Nägeli, professor of botany in Munich. With increasing boldness he tried to point out the significance of what he had found. For four years Nägeli missed the point. He wrote back to the persistent monk polite but patronising letters, and told him to try breeding hawkweed. He could not have given more mischievous advice if he tried: hawkweed is apomictic, that is it needs pollen to breed but does not incorporate the genes of the pollinating partner, so cross-breeding experiments give strange results. After struggling with hawkweed Mendel gave up and turned to bees. The results of his extensive experiments on the breeding of bees have never been found. Did he discover their strange ‘haplodiploid’ genetics?
Nägeli meanwhile published an immense treatise on heredity that not only failed to mention Mendel’s discovery; it also gave a perfect example of it from Nägeli’s own work – and still missed the point. Nägeli knew that if you crossed an angora cat with another breed, the angora coat disappeared completely in the next generation, but re-emerged intact in the kittens of the third generation. A clearer example of a Mendelian recessive could hardly be found.
Yet even in his lifetime Mendel came tantalisingly close to full recognition. Charles Darwin, normally so diligent at gleaning ideas from the work of others, even recommended to a friend a book, by W. O. Focke, that contained fourteen different references to Mendel’s paper. Yet he seems not to have noticed them himself. Mendel’s fate was to be rediscovered, in 1900, long after his own and Darwin’s deaths. It happened almost simultaneously in three different places. Each of his rediscoverers – Hugo de Vries, Carl Correns and Erich von Tschermak, all botanists – had laboriously duplicated Mendel’s work on different species before he found Mendel’s paper.
Mendelism took biology by surprise. Nothing about evolutionary theory demanded that heredity should come in lumps. Indeed, the notion seemed to undermine everything that Darwin had strived to establish. Darwin said that evolution was the accumulation of slight and random changes through selection. If genes were hard things that could emerge intact from a generation in hiding, then how could they change gradually or subtly? In many ways, the early twentieth century saw the triumph of Mendelism over Darwinism. William Bateson expressed the views of many when he hinted that particulate inheritance at least put limits on the power of natural selection. Bateson was a man with a muddled mind and a leaden prose style. He believed that evolution occurred in large leaps from one form to another leaving no intermediates. In pursuit of this eccentric notion, he had published a book in 1894 arguing that inheritance was particulate and had been furiously attacked by ‘true’ Darwinists ever since. Little wonder he welcomed Mendel with open arms and was the first to translate his papers into English. ‘There is nothing in Mendelian discovery which runs counter to the cardinal doctrine that species have arisen [by natural selection]’, wrote Bateson, sounding like a theologian claiming to be the true interpreter of St Paul. ‘Nevertheless, the result of modern inquiry has unquestionably been to deprive that principle of those supernatural attributes with which it has sometimes been invested…It cannot in candour be denied that there are passages in the works of Darwin which in some measure give countenance to these abuses of the principle of Natural Selection, but I rest easy in the certainty that had Mendel’s paper come into his hands, those passages would have been immediately revised.’4
But the very fact that the dreaded Bateson was Mendelism’s champion led European evolutionists to be suspicious of it. In Britain, the bitter feud between Mendelians and ‘biometricians’ persisted for twenty years. As much as anything this passed the torch to the United States where the argument was less polarised. In 1903 an American geneticist called Walter Sutton noticed that chromosomes behave just like Mendelian factors: they come in pairs, one from each parent. Thomas Hunt Morgan, the father of American genetics, promptly became a late convert to Mendelism, so Bateson, who disliked Morgan, gave up being right and fought against the chromosomal theory. By such petty feuds is the history of science often decided. Bateson sank into obscurity while Morgan went on to great things as the founder of a productive school of genetics and the man who lent his name to the unit of genetic distance: the centimorgan. In Britain, it was not until the sharp, mathematical mind of Ronald Fisher was brought to bear upon the matter in 1918 that Darwinism and Mendelism were at last reconciled: far from contradicting Darwin, Mendel had brilliantly vindicated him. ‘Mendelism’, said Fisher, ‘supplied