What Mendel Knew

The old adage that a prophet is not without honor save in his own country has had two innings in the case of Gregor Mendel. It was in 1865 that that remarkable man founded the science of genetics, for nothing less by way of expression is adequate to describe the way in which he enunciated its principles, the basic correctness of which has been confirmed in every branch of experimental science that has been and can be brought to bear on the subject. Like Athena, sprung fullyarmed from the brow of Zeus, genetics came out of the mind of Mendel after eight years of experimental breeding of peas, and as everything is important that relates to mental acts of creation, it is of interest to consider Mendel’s case.

Before him there were horticulturalists who hybridized plants: Koelreuter, Gaertner, Herbert, Lecoq, and Michura, to whom Mendel gave credit in his paper; but there was little to give them credit for. Their results were inconsistent, contradictory, and chaotic, and the reasons for this were that they did not know what to look for when they selected the material on which they worked. Most important of all, they started by asking questions to which their experiments on such material could not provide clear-cut answers. Mendel avoided all this unsatisfactory muddle by taking two steps which, from the point of view of methodology, were models, and of cardinal importance. In the first place he selected his material in such a way as to have parental pairs that differed in one contrasted character at a time. He found this material in peas, and, having crossed them artificially, he allowed their offspring to pollinate themselves for at least three generations. The results that he obtained were not only constant (whichever character was introduced through the seed-parent or the pollen-parent), but also revealed the appearance of the parental types among the offspring in different numbers which he counted and expressed as ratios.

THIS IS WHERE the significance of his other step can be seen: He had thought out the whole scheme of “Mendelian” segregation and recombination of factors in his head, as a theoretical exercise, on the hypothesis that the characters of the organism are controlled by discrete factors (we now call them genes) which exist in pairs; but the members of these pairs separate from one another (segregate) when the organism forms reproductive cells (eggs and pollen-cells), so that no reproductive cell contains more than one member of each pair of genes. At pollination or fertilization, which is random, pairs of genes are recombined. So, if one parent has genes AA and the other parent has genes aa, the reproductive cells formed by the former contain A, those formed by the latter contain a. When they are crossed, the hybrid has the genetic constitution Aa and its reproductive cells contain A or a. Now when two such hybrids are bred (or one is allowed to pollinate itself), the result is the expansion of a simple binomial:

(A + a) * (A + a) = AA + 2Aa + aa

This is what is known as the “one to two to one ratio,” or the “three to one ratio” if one gene is dominant over the other, so that the first “one” and the “two” look alike although they are genetically dissimilar. None of this sort of reasoning or hypothesis-making did Mendel get from the plant-hybridizers who preceded him, and Sir Ronald Fisher showed that Mendel must have worked the whole thing out in his head, because he knew what ratios to expect from his crosses before he actually made them. Fisher discovered this because in some of Mendel’s crosses, the results which he obtained were logically correct, but took no account of statistical corrections that must be applied when working with small numbers of individuals, as in Mendel’s experiments. When these corrections are applied, the results that Mendel expected and obtained are seen to be biased. His gardner must have known what his master expected, and obliged. This in itself is a matter of great interest, for enormous numbers of individuals must be used in experiments in order to get close approximations to the ratios that the theory of probabilities indicates. Even with nearly a quarter of a million individuals, the ratio of peas showing one character as compared with those showing the other, gets no nearer to the expected 3 to 1 than 3.016 to 1. It was really a great service to science that the gardener, or whoever it was performed; for if it had not been for the “model” ratio of 3 to 1, it is doubtful whether some of Mendel’s followers would have recognized the significance of such a ratio as 2.75 to 1, which Cuénot obtained with mice. This is really a 3 to 1 ratio, obscured by the departure from expectation due to the small number of individuals used in the experiments. With Shakespeare we can say:

The truth is then most done not doing it.
The better act of purposes mistook
Is to mistake again; though indirect,
Yet indirection thereby grows direct,
And falsehood falsehood cures.

IF MENDEL got no help in formulating his ideas from his plant-hybridizing predecessors, whence did he derive them, or, to use Isaac Newton’s phrase, on whose shoulders did he stand? We do not know for certain, but Robert C. Olby (Origins of Mendelism, London, 1966) has drawn attention to the fact that among Mendel’s teachers at Vienna were Andreas von Ettinghausen and, most important, Christian Doppler (of the “Doppler effect”); and both these men laid emphasis on the importance of the mathematical approach to problems. It is probable, therefore, that it was they who gave Mendel the taste (which he is known for other reasons to have had) for playing about with mathematics.

Mendel’s paper was read in 1865 and published in 1866. It is often said that it was completely forgotten until 1900, when it was independently re-discovered by Correns, Tschermak, and de Vries; but this is not quite correct. It was certainly not understood (and even then, only in part) before 1900; but it was referred to by a few authors, including Liberty Hyde Bailey in his Plant Breeding (New York, 1895). Nevertheless, it remains true that from 1865 until 1900, prophet Mendel was without honor in his own country.

After 1900, a curious state of affairs arose. In the first place the clear-cut nature of the effects of Mendelian factors as known then, appeared to provide evidence of discontinuity in evolution, and therefore a stick to beat Darwin with, because Darwin believed evolution to be gradual. This led to de Vries’s Mutation theory. Mutations are sudden and random changes in genes, which initiate heritable variation. But de Vries’s “mutations” were not mutations at all; they were reversions to parental type in very peculiar hybrids (evening primrose); and in any case, mutations that are known to be random and to bear no relation to the environmental conditions of the organisms prevailing when they occur are quite incapable of explaining the perfection of adaptations that are to be found throughout the plant and animal kingdoms. Gradually it became clear that Darwinian selectionists and Mendelian geneticists had been fighting each other because neither of the two sides knew enough about its own subject. It is true that by the start of the First World War, Thomas H. Morgan and his magnificent team—A. H. Sturtevant, C. C. Bridges, H. J. Muller—had shown beyond possibility of doubt that genes are arranged in linear order along the chromosomes in the nuclei of the cells, thereby verifying an hypothesis put forward by Walter H. Sutton in 1902. The application of Mendelian genetics to organisms living wild in nature may be said to start from the discovery by S. S. Tschetverikov that genetic analysis must be, and can be carried out on such organisms. Their heritable variation is found to obey Mendelian principles.

Meanwhile, Fisher was able to show from his experiments that far from dethroning Darwin’s selection. Mendelian genetics provides irrefutable evidence for selection, right at its heart, because the visible, structural, and physiological characters of an organism are not only under the control of “their” gene, but also at second hand under the control of the other genes which make up what is known as the gene-complex, by means of which the effects of any given gene are either reduced or enhanced. And it is selection, working through the gene-complexes, that decides whether any given gene is a handicap to its owner, in which case it leaves few offspring or dies young, or whether a gene confers advantage to its owner, in which case it leaves more offspring during the longer life that efficient adaptation to its environment allows it to live. This is the basis of the synthetic theory of evolution.

IN FACT, the entire system of Mendelian genes provides exactly the mechanism required to explain evolution by natural selection, and this is the basis of the synthetic theory of evolution. There is a further point here, which has only recently come to notice. Contrary to what had been thought, and I myself made this mistake in my Life of Charles Darwin, Mendel was not opposed to Darwin’s views on evolution. Mendel even went out of his way, in his paper, to provide Darwin with the solution to the problem of the origin of heritable variation and it is there for all to see if they only know what to look for, though it is hidden by the fact that Mendel did not mention Darwin’s name. This would have been too dangerous for a member of the Augustinian order at a time when the Emperor of Austria had made a Concordat with the Vatican. But the whole episode falls into place when it is remembered that Mendel is said to have told his friend Gustav from Niessl that there was something lacking from Darwin’s system (which was true) and that he, Mendel, hoped that his own researches would provide what was lacking; and this is also true, for the lacuna was the mechanism of heritable variation.

The synthetic theory of evolution is supported by all the leading biologists, particularly those who speak English, and the language-restriction has, unfortunately, been significant. In the Soviet Union splendid research in genetics was carried out by Nikolai Ivanovich Vavilov, whose studies on the origins of cultivated plants earned him universal respect. Unfortunately, the ear of Stalin at that time was monopolized by Trofim Lysenko, a believer in so-called Lamarckian theories of the heritability of environmental effects, which fitted in very well with political views that ascribed all characters, particularly those of Man, to nature and not to nature. So Mendel’s Law and Morgan’s genes were rejected as reactionary, idealist, bourgeois, and metaphysical. Yet Mendel’s factors were particles, Morgan’s genes were parts of chromosomes, and Watson and Crick have revealed the molecular structure of the genes in deoxyribonucleic acid. Genetics has provided the objective material and physical basis of heredity. There has never been such a mistake; but it went on: statistics as a method was altogether repudiated, and the claim was made to have proved “irrefutably” that evolution of one species took place with a bang from another species: soft wheat from hard wheat, oats from wheat, wheat from barley, etc. In all this, Lysenko claimed to be following in the pioneering footsteps of Ivan V. Michurin, a railroad worker turned gardener, who devoted much time to acclimatization, hybridization, and grafting experiments. There then occurred what Conway Zirkle only too rightly called The Death of a Science; and not only of a science, for when Vavilov was elected a Foreign Member of the Royal Society of London, there were reasons for believing that he had already died in a concentration camp.

IT IS TIME to return to Mendel. In 1908, a subscription was opened for the erection of a statue to Mendel in the gardens of the Monastery of St. Thomas at Brün, in Czechoslovakia, where his experiments were performed. (It is distressing to have to record that only de Vries refused to subscribe: If it had not been for Mendel, Mendel’s Laws would be know today as de Vries’s Laws.) After the Communist revolution in Czechoslovakia, Mendel’s statue was thrown down, in 1950. Again, he was no prophet in his own country. But now, it has been re-erected, and a splendid symposium was held in 1965, the centenary of Mendel’s reading of his paper, at Brno and at Prague, under the auspices of the Czechoslovak Academy of Sciences. It was in connection with these celebrations that the book under review was published, by Jaroslav Krizenecky, who unfortunately did not live to see it, for he died on 24 December 1964, after founding the new Gregor Mendel Department of the Moravian Museum in Brno.

This book, Fundamenta Genetica, performs the invaluable service of presenting, collected together in one convenient and attractive volume, all the basic papers on genetics from 1865 until 1903 in their original texts. Most of them were published in journals which research workers today do not find readily to hand. Mendel’s own classic paper is printed after collation with a photostat of his original manuscript (which has been lost), misprints corrected, and pagination of both manuscript and original publication indicated. The papers of the re-discoverers, de Vries, Correns, and Tschermak, are there, as are those of William Bateson and Lucien Cuénot, who showed that Mendel’s Laws also applied to animals. There is Archibald Garrod’s paper which formed the start of his studies on inborn errors of metabolism and showed that Mendel’s Laws apply to Man. Included also are papers by W. E. Castle, A. M. Glover, W. C. Farabee, E. B. Wilson, W. A. Cannon, W. S. Sutton, and C. E. McClung, which show how soundly the basis for genetical studies was laid in the United States, where Sewall Wright, Richard Goldschmidt, Curt Stern, Theodosius Dobzhansky, Ernst Mayr, and many others have never ceased to hold the banner high.

It is to be hoped that this geneticists’ charter-book will be widely known and appreciated, all over the world, and there are encouraging signs that this includes the Soviet Union. Thirty years ago, Nikolai Dubinin, following on Tschetverikov’s work, showed that wild populations of the fruit fly were chock-full of recessive Mendelian genes, a discovery of major importance because it is from such genes that the future dominant genes will be recruited when the environmental conditions of the organisms change (as they are bound to do, sooner or later), better adaptation will be achieved, and evolution brought about, for that is all that evolution is. Now, it is Academician Dubinin who is Director of the Institute of General Genetics of the USSR: genetics has been resurrected in his great land, and Mendel has again become and will remain a prophet in his own country.