Copyright © 1997 by Robert C. Olby
(This essay is made available exclusively at MendelWeb, for non-commercial educational use only, with the kind permission of the author. Although you are welcome to download this text, please do not reproduce it without the author's permission.)
Author's Note: This essay was written for a collection of historiographic studies in the winter of 1993/4, while the author was an Andrew Mellon Fellow at the Rockefeller University. It was to appear in a collection of papers on the history of genetics. As this volume has been dropped the author wishes to make this essay available through the MendelWeb. Apart from mentioning the recent papers of Ida Stamhuis and Hans Jörg Rheinberger, the paper has not been updated. The author wishes to thank Professor Wiesel and Professor Lederberg for accepting him into the Rockefeller University, and the Mellon Foundation for financial support. Also thanks are gratefully given to Professor Darden for her careful reading of the text and her suggestions for clarification, and to Roger Blumberg for his careful preparation of the text for MendelWeb.
'Each generation, perhaps, found in Mendel's paper only what it expected to find; in the first period a repetition of the hybridization results commonly reported, in the second a discovery in inheritance supposedly difficult to reconcile with continuous evolution. Each generation, therefore, ignored what did not confirm its own expectations.' (R.A.Fisher, 1936, p.171)Contents
As the twentieth century has unfolded the new science of genetics has come to occupy an increasingly important position at the center of the sciences of life. Once a mere aid to the agriculturist, horticulturist, and eugenicist, kept far removed from the core of biology, productive links with other biological disciplines nevertheless began to form, first with cytology and then with evolutionary studies. In the second half of the century genetics became allied with biochemistry; it revolutionized bacteriology, played a major role in the emergence of the molecular biology of the fifties, resisted the challenge of ecology, took hold of cancer research and is even now reaching out to revolutionize taxonomy and its old rival embryology.
Such a science, arrived but yesterday, and today transformed from Cinderella to Queen, deserves a history as dramatic as its intellectual and disciplinary successes. To be sure, it has not been difficult to tell a story of pathos and triumph. First it is claimed that the origin of the science of genetics can be traced to one man - Gregor Mendel (1822-1884), raised in German-speaking Silesia, who entered the Augustinian order in the Monastery of Brünn, Moravia, and taught high school science, also finding time to conduct experiments in the hybridization of plants, before becoming abbot of his monastery. He died in comparative obscurity; when the report of his genetic researches was published in 1866 it remained little-known outside a small circle until 1900. Then came the dramatic and simultaneous rediscovery of his laws of heredity and the discovery of his paper by three scientists in 1900. Still, his work was treated with disdain by most biologists - embryologists saw Mendelism as a threat, systematists considered it an irrelevance, and Darwinians failed to realize how it could be brought into harmony with their view of evolution. There followed the great 'trinity' of R.A. Fisher, J.B.S. Haldane and Sewall Wright, who welded Mendelism and Darwinism together to create what is known as the 'evolutionary synthesis,' around 1930. Thirty-four years of neglect, thirty years of blindness, and still genetics had no more than announced its 'marriage' to Darwinism. Or had it, rather, done little more than 'come out' like a debutant to claim attention?
Twenty-three years further on and we come to the celebrated announcement by J. D. Watson and F.H.C. Crick of a structure for DNA that claimed the gene is made of nucleic acid and furthermore, suggested how it might replicate, mutate, and be expressed. The maturity of genetics was in sight! Gone was the isolation of physiological genetics from transmission genetics. The image of 'classical genetics' as so much counting of progeny - referred to scornfully by its critics as 'bean bag genetics' - was no longer appropriate. Genetics was now 'molecular', and in this guise it could be placed at the center of the biological sciences.
Such a thumb-nail sketch of the subject is both heroic and dramatic. It offers a clearly structured narrative with precise bench marks - 1865, 1900, 1930, 1953 - whereby periodization can be clearly visualized. The foundation stone was laid in 1865. It was unearthed in 1900. There followed much 'counting of beans' by which 'classical genetics' was established. Then came the 'marriage' of Mendelian genetics with Darwinian evolution, an event which played a key role in the restructuring of the life sciences, but it was not until the gene was molecularized in 1953 that the science of genetics took its rightful place at the center of biology. This representation of the biography of genetics is well suited to those textbooks whose authors use history to introduce their subject. It serves, also, to establish a preliminary landscape into which to fit the the historical events. Then let us use it thus, whilst reserving our right to criticize it.
The merit of the above sketch for this essay lies in the contrasting caricatures of genetics which it depicts. Caricatures always overemphasize certain features of their subjects, thus enabling us all to recognize them. But these features do correspond with the public image of the subject in the scientific community at that time, and it is the theme of this essay that these images provide the context in which Mendel's work has been interpreted differently in the different periods. This is the reason for giving special attention to the nature of scientific disciplines in this historiographic discussion.
II. Scientific Disciplines
Scientific Disciplines, like commercial organizations, employ a variety of strategies to assert their authority, to claim their legitimacy, and to protect their interests. Banks and insurance companies place their head offices in expensive buildings located in prestigious parts of town. Universities invite famous people to lay foundation stones as the symbolic act marking the beginning of construction, and later to preside over the formal opening of new buildings. Scientific professions signify their importance by commissioning statues of their founder or founders. For a founder who is still alive they publish a Festschrift composed by his students and admirers, and for those deceased they hold public meetings to celebrate their achievements using as their excuse the centenaries of their founder's birth, major publications, and death. In the process the founder's work becomes aggrandized, his achievements more heroic, the odds he faced even more insurmountable. The American historian, Paul Forman, has suggested that this process leads to the creation of a 'myth of origins' which he has likened to those which in primitive societies 'recount the story of the original ancestor of a clan or tribe.' In some cases the 'ancestor' or 'founder' possessed extraordinary prescience which others did not share. Consequently his work was not understood. Because he was 'ahead of his time,' his work was ignored only to be rediscovered years later.
Now a discipline represents more than a subject domain in the sciences. To be sure, disciplines can in certain cases be clearly identified by their subject matter: thus, meteorology concerns clouds and rain, not flowers and insects; ornithologists train their binoculars on birds, not frogs; and virologists view their subjects through electron microscopes, not optical microscopes, let alone binoculars! But beware, because such clear demarcation by subject and methods is rare. Consider colloid science, biochemistry, and molecular biology. Are these disciplines, and if so how are their domains distinguished from one another? If there are border disputes, who blows the whistle and how are such disputes settled? This takes us into what is known as the political ecology of disciplines. Viewed from this aspect, disciplines are seen to emerge and maintain themselves by the wielding of power and the conscription of support. The motivation to such action is the desire for institutional and financial independence. Thus the study of physiological function was formerly a part of the discipline of anatomy, but in the nineteenth century Claude Bernard in France and Michael Foster in England succeeded in breaking away from anatomy and establishing physiology as an independent discipline. Foster then turned to the history of physiology and traced the discipline back to the physiological studies of the great anatomists from the sixteenth century onwards. History was conscripted in support of the claims of the discipline.
The danger lurking in such an exercise is the tendency to view past events in the light of the subsequent character of the discipline - a form of 'whiggish' or 'presentist' history. Therefore we need to be on our guard when we read historical papers delivered at symbolic meetings marking salient dates in the formation of a discipline. And when we leaf through the collections of 'selected papers' in this or that discipline we should be alert to the editors' policy of selection. Are there systematic omissions? Have some sections of the chosen papers been left out, and for what reasons? Nor should we drop our guard when consulting the biographies of scientists honoured as founders of disciplines, for biographies can be deployed in the service of a scientific discipline just as well as can political biographies in the service of a political party.
Yet all this talk of political ecology does not exhaust our subject. Disciplines do not just arise by force of arms. They must have some object and some novelty - either they must build upon the discovery or construction of an entity that had not been appropriated by an existing discipline, or they must deploy a new strategy or instrument wherewith to search for novelty. Thus ferments were well known in nineteenth century physiological chemistry but were not identified as key concepts until the turn of the century when they became closely identified with the new discipline of biochemistry, following Eduard Büchner's isolation of zymase in 1897. Thus biochemistry did have a 'core concept,' and this in turn had a longer history. Equally, genetics had a core concept in the Mendelian factor or 'gene', but the history of theories of particulate inheritance can be traced back to the eighteenth century. Histories of disciplines thus speak of their long history but short life, identifying their birth with a threshold - for genetics the Mendelian experiment, for psychology the psychophysical experiment, and for X-ray crystallography the technique of X-ray diffraction analysis. Mendel's experimental analysis of heredity was the "significant achievement," to use T.S. Kuhn's terminology, constituting the threshold for the crystallization of the discipline of genetics.
III. Mendel as Founder
There is no question that Mendel is considered the father of the discipline of genetics. Not, surely, as the person who institutionalized genetics. Far from it. The name itself was first publicized in 1906, twenty-two years after Mendel's death. The occasion was the third international conference on plant hybridization, the first to carry the name genetics in an alternative title. The speaker was William Bateson, and his theme was the need to establish this new discipline. We have no record that Gregor Mendel ever made any such appeal, nor do we know of reasons which would have justified him to do so. Then why call him the founder? Has there been a mistake? The British evolutionist, Sir Gavin de Beer, had no doubt on the matter. In 1965, the centenary of Mendel's famous paper, he declared on the radio: 'There is not known another example of a science which sprang fully formed from the brain of one man.' To an audience at the Royal Society that year he delivered an address with the title, 'Genetics: The Centre of Science', in which he explained himself more fully:
It is not often possible to pinpoint the origin of a whole new branch of science accurately in time and place . . . But genetics is an exception, for it owes its origin to one man, Gregor Mendel, who expounded its basic principles at Brno on 8 February and 8 March 1865. (De Beer, 1966, p.154)
What were these principles? Before we answer that question let us identify what we regard as the principles of the science we know as genetics. Clearly the experimental approach is that of cross-breeding, but this method as used by the practical breeder is not enough. The forms crossed must be of proven constancy of type, the character differences need to be recorded for all parents and offspring so that their hereditary transmission can be followed from generation to generation, and the numbers of offspring raised need to be sufficient to yield statistically significant results. For anyone who has read Mendel's paper of 1865 there is no question that Mendel did enunciate these principles. Over the years 1856 to 1861 he raised some 10,000 plants of varieties of the edible pea (Pisum sativum) which he had tested for purity of type over a two year period. He followed the transmission of seven specially selected traits - round-seeded plants with wrinkled-seeded plants, tall plants with short, green-seeded with yellow-seeded, etc. He self-fertilized their progeny to discover if they returned or reverted to one or other of their originating forms. He found that they did, but in a quite remarkable manner. When he surveyed the total number of hybrid offspring carrying one or other of the contrasted characters - tall or short, etc. - they showed an integral relationship, one contrasted character being present in three times as many plants as the other. This 3 : 1 ratio [and its resolution into the three-fold ratio 1 : 2 : 1] formed the key to the genetic analysis of all hereditary traits conforming to Mendelian heredity.
What of the theoretical interpretation? The geneticist immediately turns to the gene. This unit of inheritance is considered to be a material particle lying on a chromosome and responsible for the transmission of certain heritable characters. There are normally two copies of each gene in all somatic cells of the organism, but the members of each pair separate in the formation of the germ cells so that each gamete contains only one member of every pair. In sexual reproduction the genes from two individuals are brought together and recombined in all possible combinations in the progeny, but not all combinations are equally likely because genes on the same chromosome are linked together. The closer they are the tighter the linkage, and the less probable the recombination.
Hence, once we include theoretical interpretation it is clear that our subject is the phenomena of heredity and variability and their physical basis. Heredity and variability are thus not two opposing forces, the one an expression of the internal nature of the species, the other the impact upon it of the environment, but two sides of the same coin. The constant presence of the same gene in successive individuals yields constancy of type and underlies what used to be called the strength of heredity. Recombination of genes yielding new combinations results in variability. Brought into cultivation, wild plants vary much more, not because of the change in the conditions of existence as Darwin and most of his contemporaries maintained, but because of the unusual opportunity thus afforded for genetic recombination through crossing. Attentive readers who have persisted to the end of Mendel's paper (but not those reading the reprint in James Peters' Classic Papers in Genetics which, like many other reprints, has omitted the last section) can grant that Mendel held the view of the relation between genetic recombination and variation described above. The evidence for this is to be found beautifully expounded in the final section where he interprets the results of previous hybridists' experiments in terms of his theory.
It is another matter when we come to the the particulate basis of the results which Mendel described. Clearly he held a material theory of the life processes of the cell, for he wrote: 'This development [of the organism by cell formation] proceeds in accordance with a constant law, which is grounded in the material constitution and arrangement of the elements which achieved vivifying union in the cell.' (Mendel, 1866K, p.88) Then surely he must have conceived of particles of some sort like our genes? And did he not do so despite not having seen or heard of chromosomes (a term introduced 23 years after Mendel delivered his paper)? The geneticist, Guido Pontecorvo, expressed his concern on this point when he wrote:
Mendel did not distinguish explicitly between factors and characters in his papers and perhaps he did not even have this distinction clear in his own mind; yet we have no alternative but to read it in his paper, which would make no sense without it. (Pontecorvo, 1966, p.169)
In other words, he does not state the theory of the gene, but he must have held such a theory and if we try hard we can 'glimpse' it between the lines of his text. Why have so many authorities been pressed to such a conclusion? Is it because Mendel was the founder and hero of their discipline or are there other reasons? To be sure, no careful reader of his paper can come away without being deeply impressed with the precision of his language. His strategy was to describe the genetic composition of cells and their contents in terms of the adult forms to which they gave rise. But he did not keep rigidly to this strategy. For example consider the following sentence: '. . . pea hybrids form egg and pollen cells which, in their composition, correspond in equal numbers to all the constant forms resulting from the combination of traits united through fertilization.' (Mendel, 1866, S&S, p. 29). He started well but then slipped into 'traits united through fertilization' instead of elements united. Likewise, where we would speak of dominant and recessive genes or factors, Mendel wrote of traits.
The more we pry into the language of Mendel's text the less confident do we become that he had the concept of the gene in mind when he wrote it. But, you object, he proposed the law of segregation. Did he not state that the two elements which determine alternative expressions of the same trait (e.g., round/wrinkled seeds) separate in the formation of the germ cells, with the result that only one of them is to be found in any of the germ cells? No! He wrote: 'In the formation of these [germ] cells [of the hybrid] all elements participate in a perfectly free and equal arrangement, whereby only the differing elements are mutually exclusive.' In quoting this and similar passages in 1979, I wrote:
It is all too easy to invest these passages with significance born of hindsight. Granted that Mendel was committed to a materialist explanatory framework, i.e., that the characteristics of living organisms are determined by material entities in the cells. Admitting that he was seeking an explanatory hypothesis in harmony with the cell theory, in particular with the cell theory of fertilization, how far did he go in his conception of a particulate theory of heredity? First it is evident that he did not conceive of pairs of elements in the cell representing and determining the pairs of contrasted characters. If he had this conception he would have allowed a separation between like members of such pairs as well as between unlike members. His statement that 'only the differing elements are mutually exclusive" is in conflict with classical Mendelian genetics. If it were true [and assuming he had the concept of a pair of factors for each character pair] the number of like elements determining a character would increase every time the germ cells fused in fertilization. Mendel cannot therefore have had the conception of a finite number of hereditary elements which in the simplest case is two per character [pair]. (Olby, 1979, p. 70)
Added to this evidence is the well-known absence of double letters to represent the pure breeding offspring of hybrids in Mendel's scheme. Thus the three classes in this second hybrid generation (F2) are given the symbols: A + 2Aa + a rather than AA + 2Aa + aa. If these letters refer to the hereditary elements or factors to which Wilhelm Johannsen later gave the name 'gene', we would expect Mendel to have used double letters for each class. To defend Mendel's claim to the gene concept geneticists have indulged in special pleading thus: 'It is but an abridged way of expression. It was perfectly clear to Mendel that those elements occurred paired in homozygotes . . .' Or: 'throughout the papers (and even in his later correspondence with the botanist Nägeli) he has described the three classes of individuals in an F2 as A, Aa and a, evading the unproved doubleness of the "homozygote" AA class.'
Now suppose we dismiss these excuses as special pleading and accept that the concept of the hereditary factor or gene of the early Mendelians is not present in Mendel's papers, and was not in his mind. What grounds are left to support Mendel's claim as founder? First, he introduced the experimental methodology upon which Mendelian genetics has been built. This centered on the character-pair rather than on the species. His experiments were organized in terms of the character-pairs and their results were arranged in terms of them. The character-pair was moreover a novel concept introduced by Mendel and in terms of which he defined dominance and recessiveness. Second, Mendel not only counted hybrid progeny and classified them in terms of these character-pairs, but he perceived in the numerical relationships between the different classes approximations to simple integral ratios. Other hybridists counted progeny - even recording what with the light of hindsight we can call Mendelian ratios - but they did not perceive their data in this way. It is an empirical fact, recorded by Charles Darwin, that the progeny from hybrids between the normal and the peloric snapdragon showed reversion: 88 normal to 37 peloric, and 2 intermediate. If we discount the intermediates we have a ratio of 2.38 :1. But how did Darwin perceive it? Besides there existing a 'strong latent tendency to become peloric', he remarked, 'there is a still stronger tendency in all peloric plants to reacquire their normal irregular shape.' He went on to lament that prepotency varied so much in strength, 'even in regard to the same character, in different animals.' Therefore he was not surprised that 'no one has hitherto succeeded in drawing up general rules on the subject of prepotency.' (Darwin, 1868, vol.ii, p.45-46) In a like manner, Hugo de Vries, only a year before he rediscovered Mendelian ratios, recorded F2 figures for corn of 3167 yellow to 1092 white seeds. This is a ratio of 2.90 : 1. But what did De Vries comment? Merely that these corn hybrids were capable 'of reproducing the types of their two parents.' (De Vries, 1899, p.973) Thus a Mendelian ratio is not an empirical fact but a theory-laden one. It is the theoretical component that identifies certain data among a host of figures as peculiarly significant.
This brings us to the central point of Mendel's paper, namely the parallel between hybrid variation and the equations of combinatorial mathematics. The simplest of these equations is the binomial. Its 'expansion' or 'development' , as we all know, goes as follows: (A + a)^2= A^2 + 2 Aa + a^2, or AA + 2Aa + aa. This expansion was known as the binomial law. Mendel used the word law ( Gesetz) to describe the way in which hybrid progeny display in their numerical relations the very same binomial law. He did not use that word to describe the independent transmission of the several character-pairs - the phenomenon we know as Mendel's law of the independent assortment of characters - nor to describe germinal segregation - the law of segregation - but only to describe the development of progeny. It was, so to say, a law of embryological development governing the form which the mature organism would assume. It was as if the hybrid in reproducing, expanded the binomial equation! And the beauty of the process lay in the fact that this basically stochastic process conformed in its results to the binomial law. Here was indeterminacy yielding a law-following result, where the law in question can be expressed by a simple algorithm.
This was Mendel's first step towards the goal he had set himself of accounting for the hitherto confusing medley of results from previous researches in hybridization. His next step was to demonstrate that the character-pairs he studied behaved independently (at least he thought so). He convinced himself of this when he demonstrated that all possible recombinations of the traits were represented in the progeny and in proportions close to those predicted by combining the terms from the expansion of a binomial equation for each character-pair.
By introducing the statistical approach and combinatorial mathematics into the subject of hybridization alongside his concept of the character-pair Mendel surely earned his place as founder of genetics. He did not need to have the concept of the gene. It was his successors who made the move from the character-pair to the allelomorph, or pair of mutually exclusive factors or genes. Yet, objects the sceptic, was Mendel's work not ignored with the result that others had to rediscover it? Not quite. The label rediscoverer is a slippery one. We now possess evidence that neither Hugo de Vries nor Erich Tschermak arrived independently of Mendel at his theory, although Tschermak did perceive the 3:1 ratio in his F2 data in 1900. Not till De Vries had read Mendel (possibly for the second time) did he reorganize his data and from them select those experiments which confirmed Mendel. Just how little importance De Vries attached to these Mendelian results has been established recently by Ida Stamhuis (Stamhuis, 1996, also see Meijer, 1985). Even Correns who, like Tschermak, claimed to have noted the 3:1 ratio by himself, had in fact read Mendel's paper in 1896 and, one suspects, forgot about it (Rheinberger, 1996). He certainly benefited from reading it again in 1900. Here we should remember that Mendel's data were more impressive than that of any of his rediscoverers. De Vries worked with some fifteen species, but his numerical data were not as large and striking as Mendel's data from one species.
There were, naturally, other reasons for settling on Mendel as founder. First his priority was undisputed. Second, he served to neutralize any disputes between the three rediscoverers themselves. (The attribution of founder status to an older scientist - especially if he or she is deceased - is a convenient way to achieve social harmony in science.) Third, his paper is a model of brevity, positivist caution, exemplary planning, and clear presentation. Fourth, as a resident of Moravia (albeit ethnically German) in Austro-Hungary, he belonged to a suppressed people for whom there was widespread sympathy. This, as we shall see, was expressed at the unveiling of Mendel's statue in Brno on the centenary of his birth, when anti-German feelings amongst scientists were strong and the sorely oppressed Czechs and Slovaks had justly been granted nationhood. Such appropriate timing served genetics well, when in 1965 geneticists were able to celebrate the first signs of the demise of Lysenkoism in the city in which Mendel had performed his experiments and described the results.
IV. Mendel and the Darwinians
A powerful influence upon the interpretation of Mendel's work and the nature of his unspoken views have been the Darwinian evolutionists. We have already encountered Sir Gavin de Beer. Two more significant interpreters are Hugo Iltis, in his biography of 1924, and R.A. Fisher, in his famous analysis of Mendel's paper (Fisher, 1936). As Darwinians these authors were keen to exhibit Mendel as a supporter of Darwin. Therefore his work was intended to clarify the uncertainty over the longevity of new variations in outbreeding populations. If they were progressively diluted in the wild they could not give rise to new species - the problem of the 'swamping effect of crossing' which worried Darwin so much. Yet here in Mendel's research lay the solution: character differences are not blended but persist. The process of hereditary expression is distinct from that of hereditary transmission. Blending relates to the former, persistence to the latter. Oh, if only Darwin had met Mendel, or even read his paper - how different would the history of biology have been! In support of this conclusion the Darwinians, led by Sir Gavin, have been very anxious to gain support for their assumption that no such meeting ever occurred. Mendel came to Britain for the Industrial Exhibition held in London in 1862; but, as Sir Gavin has found, Darwin was not even at his house in Down, let alone in London at that time (De Beer, 1965), and Darwin never left England's shores after returning from the voyage of the Beagle in 1836. Although Mendel visited Vienna several times after completing his experiments, police records show that he never strayed far from Moravia.
Behind this exercise in document searching lay the assumption that the thirty-year 'delay' in achieving a 'marriage' between Darwinian evolution and Mendelian heredity could have been avoided. Had communications in science been better, Darwin would have learned of Mendel's work on the basis of which he could have rejected the claims of the critics that new variations would rapidly be swamped and hence that evolution cannot have proceeded by the preservation of adaptive variations under the influence of natural selection. Then biologists would have accepted natural selection before the 1930s. This Darwinian view of our founder figure implies that, as Loren Eiseley wrote, Mendel was 'The Priest who held the key to Evolution'. If the value of Mendel's work was so obvious, the failure of his contemporaries to appreciate it must have been due either to ignorance or to the inadequacy of the system of disseminating scientific information. Franz Weiling has laboured hard to unearth references to Mendel's 1865 paper and he has found many. Hugo Iltis, Vítezslav Orel, and his Czech colleagues have researched the scientific credentials of those around Mendel in Brno who knew his work, and have shown that many among them were seriously interested in the theory of evolution and in Darwin's work. Yet as Eiseley expressed it poetically:
Stolidly the audience had listened . . . Not a solitary soul had understood him. Thirty-five years were to flow by and the grass on the discoverer's grave would be green before the world of science comprehended that tremendous moment. . . No man who loves knowledge would want an episode like this to happen twice. (Eiseley, 1959, pp.206-207)
We can see, now, how this Darwinian view of Mendel raises problems for the historian. Why did Mendel not mention Darwin's name or natural selection in his paper of 1865 whereas he did mention him in 1869? Then he wrote:
The question of the origin of the numerous and constant intermediate forms has recently acquired no small interest since a famous Hieracium specialist [Carl Nägeli] has, in the spirit of the Darwinian teaching, defended the view that these forms are to be regarded as [arising] from the transmutation of lost or still existing species. (Mendel 1869, S&S, p.51)
Are we expected to believe that the Augustinian order or the local Catholic bishop would have prevented him from referring to Darwin in 1865 but permitted him in 1869? That sounds suspiciously like a case of special pleading. In any case, how could Mendel have envisaged the nature of Darwin's theory and the locus of its weakest point when he planned his experiments in 1852, and began testing varieties of the edible pea for constancy of type, eight years before the first German translation of Darwin's Origin of Species, and ten years before the edition (2nd.) which Mendel purchased and annotated? How was it possible for Mendel to have such modern views? To say that his work was 'premature' hardly solves the problem, for what causes prematurity? Did he invent these 1930-ish views simply out of thin air?
Suppose we forget this Darwinian Mendel for the moment and, following the suggestion of L.A. Callender, substitute a 'Linnean' Mendel instead. According to this view Mendel's research in hybridization was in the tradition of Linnean botany which accepted that the species we know today are the children of the crossing of fewer primordial forms. (Callender, 1988) This we can call 'species multiplication by hybridization'. It was the research program that the eighteenth century Swedish botanist, Carl Linnaeus (1707-1788), set for several of his students in the 1750s and 60s. It followed logically from Linnaeus' acceptance of the sexuality of plants, for unlike animals plants lack the instinctive behavioral aversion to breeding with members of other species. Strange to relate, the debate over the claim that plants reproduce sexually continued well into the nineteenth century, and alongside it the corollary that plant hybridization leads to the multiplication of species. Thus in the nineteenth century three prizes were offered by the scientific academies of Holland, France, and Prussia for essays reporting experiments which addressed these questions. The prize winners were Mendel's predecessors in hybridization - the Swabian botanist, Carl von Gärtner (1772-1850), the French botanist, Charles Naudin (1815-1899), and the Prussian physician, A.F. Wiegmann (1771-1853).
According to the majority of systematists and naturalists in the 1850s most hybrids do not perpetuate themselves, because they tend to revert to their originating species. But as botanists searched and recorded the floras of their localities in order to publish local floras (many appeared in the 1850s and 60s) they discovered numerous naturally occurring hybrids. If these did not revert they could form 'constant hybrids'. Such would surely deserve the status of new species. In Breslau, the lawyer Max Wichura (1817-1866), who had become a world expert on willows, not only recorded willow hybrids growing in the wild, but he produced many experimentally. In Vienna one of Mendel's teachers, the plant physiologist Franz Unger (1800-1870), taught species transmutation and suggested hybridization as a source of new species. Another of Unger's students and a contemporary of Mendel, the famous Austrian botanist Kerner von Marilaun (1831-1898), began reporting on naturally occurring hybrids from 1859, twelve years later publishing his strong support for the origin of new species from hybridization under the title 'Can Bastard Forms become Species?' (Kerner, 1871). Could it be the case that Mendel, too, was primarily concerned with this possibility? Clearly he did not consider his theory of germinal segregation of character-pairs was the end of the story for he confessed in 1869:
. . . we do not possess a complete theory of hybridisation, and we may be led into erroneous conclusions if we take rules deduced from observation of certain other hybrids to be Laws of Hybridisation, and try to apply them to Hieracium without further consideration. (Mendel, 1869, S&S, p.52)
Let us, in opposition to the Darwinians, assume that the answer to the question: "Can hybrids form new species?" is yes, or at least that the burden of proof lies with those who deny it. What follows? First, Mendel had no need to learn about Darwin's views in order to plan and execute his experiments, nor did he need to refer to him in 1865. Second, his study of the edible pea did not lead him to reject the concept of species multiplication by hybridization. Instead it led him to study other species, especially in the genus Hieracium, in the expectation of finding evidence in support of that theory. Third, no 'evil genius' has to be invented, who led him in the 'wrong direction'. The eminent botanist, Carl von Nägeli (1817-1891) encouraged Mendel in his study of this genus only after Mendel's experiments were well under way. Fourth, Mendel's misrepresentation of the views of both Gärtner and Wichura on the existence of constant hybrids can be attributed to his optimism that such could be found. Although Gärtner produced a list of nine such hybrids, he doubted that they could form new species because of a loss of fertility and disintegration of the type. Mendel chose not to mention this qualification. As for Wichura, Mendel's misrepresentation of his claims is striking. The Breslau botanist recognized that many willow hybrids are perpetuated by asexual means, thus giving rise to whole clusters of hybrid plants, but he twice demonstrated reversion of willow hybrids experimentally. Yet as late as 1869 Mendel cited Wichura as claiming that his willow hybrids 'propagated themselves like pure species.' (Mendel, 1869, S&S, p.55) Such behavior is extraordinary for our Darwinian Mendel, less so for our Linnean Mendel.
Consider, now, our Darwinan Mendel searching for the laws of the transmission of characters, as we would expect our first geneticist to do. How odd, then, it is that the terms 'heredity', 'hereditary transmission', and 'laws of heredity' do not appear in the title of the paper, but instead we have 'Experiments on Plant Hybrids'. And the goal of his experiments is to discover a 'generally applicable law governing the formation and development of hybrids', for this is 'the only right way by which we can finally reach the solution of a question the importance of which cannot be overestimated in connection with the developmental history of organic forms.' (Mendel, 1866, p.57-58) The significant German word here is Entwicklungsgeschichte. This referred to the unfolding over extended periods of time of the biological diversity of species both extant today and those now extinct. It carried the sense of internal generation and transmutation. The term Evolution, on the other hand, was used at this time for embryological development not transmutation. This shows clearly that Mendel's paper has to be viewed in the context of the transmutationist debate in German-speaking central Europe which ante-dates the work of Darwin. A thread running through these debates was the notion of a law-following developmental process of transmutation yielding new species. Consequently it is very misleading to transpose Mendel's work from its source in the Austro-Hungarian empire to the world of Darwinian debates in Victorian England and America. And further, it belongs to the debates within botany, not zoology. The case for the hybrid origin of animal species was not vigorously pursued at this time, and indeed has since been shown to occur but rarely.
V. Mendelism and the Nature of Biology
It is well known that the science of statistics gestated in the realms of political arithmetic and theology, finding its way into science through the discussion and determination of experimental error. The physicists took the next step in adopting a statistical view of heat and creating statistical mechanics. Following Quetelet's work on the 'average man', Darwin generalized the Belgian's Gaussian error distribution to provide a populationist conception of species. He also introduced probability into the discussion of adaptation by attributing this feature of living things to the selection of individuals within a population showing variation, which was distributed in a Gaussian manner. Mendel also adopted a probabilistic interpretation of the process of hybrid reproduction, and from such a position he was able to devise a scheme that yielded a law-following distribution of the characters. This, as we have seen, could be expressed in the terms of a binomial equation. This law described the outcome of processes observed under experimental conditions. It was not an historical explanation based on evidence dragged up from the past or invented in the heat of speculation. Rather, like the formula C(n)H(2n+2) for the series of alkanes, it could serve to represent the results of a whole series of experimental results.
It is difficult to rid ourselves momentarily of the confident view many of us have deep-down concerning the superiority of the Darwinian view of nature over alternatives that rely on internally generated developmental processes. Unless we can rid ourselves of this prejudice we are likely to adopt a normative and judgmental attitude to such alternatives. But it is clear that many biologists in both this and the previous century yearned for a science of biology that was more like chemistry than political arithmetic or archeology. To glimpse Mendel in his own context we need to adopt a sympathetic attitude to this point of view. Consider the zoologist, Hans Driesch. He was opposed both to Darwinism and to Weismannism. Behind this opposition lay his conception of scientific explanation and rational science. To explain, he wrote, 'means to subsume under known concepts, or rules, or laws, or principles, whether the laws or concepts themselves be "explained" or not. Explaining therefore is always relative.' (Driesch, 1908, p. 51) He added that science should do more than arrive at empirical generalizations, and it should not be satisfied with historical causal descriptions as did the phylogenists. Science should also be rational. Thus rational systematics 'is founded upon a concept or upon a proposition, by the aid of which a totality of specific diversities may be understood.'
It is common knowledge that the turn of the century was a time around which we note a transition from descriptive to experimental research in biology. The development of Mendelian genetics and the expansion of experimental work in both embryology and cytology are noteworthy examples. A salient point in the body of received knowledge of the nineteenth century, which came under attack, was the doctrine of recapitulation, that the embryo in the course of its development passes through the successive stages of the evolutionary history of the species to which it belongs. It is no accident that one of the most effective critics of this doctrine was the zoologist who was foremost in establishing Mendelian research in the English-speaking world, William Bateson (1861-1926). In the 1890s he suspected he had found, in the processes of repetition and organization of parts, the key to both variation and heredity. Variations due to these processes he called 'meristic.' An example of the variation in repetition was supernumerary digits, and of changes in organization peloric - for instance peloric flowers - where a species bearing radially symmetrical flowers yields offspring with flowers that are bilaterally symmetrical. Now meristic variation is ultimately based upon cell divisions. When Bateson read Mendel's paper in 1900 he gladly accepted the hypothesis of germinal segregation expressed therein. The determinants for differing character pairs separated and passed into different germ cells. Genetic recombination followed, yielding individual variation among the hybrid offspring, but the variation was not continuous as claimed by the Darwinians, but discontinuous; in Mendel's experiments, seeds were either round or wrinkled, yellow or green, etc. Like Bateson's meristic variations they did not grade imperceptibly the one into the other.
Equally important to Bateson was Mendel's demonstration of the conformity in the distribution of this variation with the terms of the binomial equation. The Mendelian ratios, in short, supplied biology with the equivalent of the stoichiometric rules of chemistry, as Bateson himself expressed it. Here was the reign of law, the ability to predict, the foundations for which were laid in the study of observable and quantifiable processes. Thus equipped, biology could achieve an enviable status alongside chemistry. A research program stretched out before Bateson's gaze in which one species after another would be investigated to discover the combining powers of its characters. He dreamed of the establishment of a 'periodic table' not of the elements, but of the Mendelian factors, and he yearned for the coming of a Mendeleev for biology. Away with imagined scenarios of selection and visionary tales of phylogenetic history. Abandon the comparative anatomist and turn instead to the horticulturist, the agriculturist, and the breeder of stock. These were Bateson's cries.
The 3:1 and 9:3:3:1 Mendelian ratios were, for Bateson, only the starting point. He went on to suggest that by interaction between hereditary factors it would be possible to realize all possible combinations of the merging of the classes of offspring. Thus, in the F2 generation of a two-factor cross, the normal Mendelian ratios are those between 4 classes made up of 16 terms:
where the phenomenon of dominance, or the masking of one character by its "opposite", has reduced the number of terms. Bateson and his co-workers were able to find examples of other series:
In 1911 Bateson and his co-worker, R.C. Punnett, introduced their Reduplication Hypothesis. This represents a further step in developing this 'rationalist' program to deal with exceptions to the rule of the independent assortment of characters. When Punnett and he discovered what they called 'Partial Gametic Coupling' or what we call Linkage, they believed they could account for it by a further modification of the fundamental Mendelian ratio. They suggested that the classes of gametes bearing different combinations of factors were produced in different proportions, thus breaking the Mendelian rule that each kind of gamete is produced in equal numbers (i.e., 1 : 1 : 1 : 1). He envisaged the process by which this was achieved in terms of successive cell divisions which, because some cell types suffered more divisions than others, produced the gametic proportions and resulting relative frequencies of offspring (the zygotic ratios). Bateson was enthusiastic about this hypothesis because it could be formulated as a mathematical expression: (n - 1) AB : 1 Ab : 1 aB : (n - 1) ab (for the gametic series where 2n = number of gametes in the series). And for the zygotic series: 3n^2 - (2n - 1) : 2n - 1 : 2n - 1 : n^2 - (2n - 1).
The Reduplication hypothesis was thus a 'rational' theory in the sense that it predicted the existence of certain gametic series in accordance with a mathematical rule. The chromosome theory of Morgan was not like this. It was a purely stochastic process with no limitations upon the possible varieties in F2 results. It was opposed to Bateson's very fundamental and long held view of heredity as the result of symmetrical cell division.
VI. Bateson's Mendel
There are many striking similarities between the conceptions of science held by Bateson and by Mendel. Neither was attracted to purely descriptive biology. Both looked up to the physical sciences and prized the mathematization of their science. True, Bateson was a poor mathematician, and he was scornful of the statistical theories of the biometric school, but as we have seen in the previous section, once he had read Mendel, he sought solutions to all his breeding data in the manipulation of combinatorial formulae. Accordingly, the kernal of Mendel's theory was for Bateson the 'purity of the germ cells' and the combinatorial processes that ensued. The former was the result of Mendel's postulated germinal segregation, the mechanical process which ensured the non-blending of Mendelian factors. Mendel thus supplied Bateson with further ammunition for his near decade-long campaign to convince biologists that it is the non-blending variations that are significant for evolution. Recognition of this point implied that natural selection might not be as influential in the creation of adaptive change as the Darwinians maintained, for variations that appear abruptly per saltum do not need selection to accumulate a succession of small steps.
Bateson saw the neglect of Mendel's work as the result of the popularity of one side of the Darwinian research program - that of comparative anatomy in the service of phylogenetic reconstructions. The other side of Darwin's work - so well described in The Variation of Animals and Plants under Domestication (Darwin, 1868), in which Darwin recorded the many empirical facts he had collected from practical men (pigeon fanciers, the breeders of poultry, sheep, horses, cats, and dogs) - had been ignored. Yet it was here and from experimental hybridization that the biologist should be looking to discover the sources of variation, for without variation there would be no evolution.
Bateson's image of Mendel was clearly colored by his strong opposition to the scientific credentials of late nineteenth century Darwinian research. Mendel held the key to evolution, but it was not the same key as Loren Eiseley believed (see section IV), for it was opening a vista in which variation, not natural selection held sway. Clearly Bateson was using Mendel in support of his bold attempt to redirect evolutionary studies toward experiment, and to align them with the work of the practical man. The fact that Mendel was so good an example of just such an alignment served Bateson well in his persistent and largely successful efforts to gain funding and institutional status for Mendelian researches. His picture of Mendel's theory of hybridization was colored also by his dislike of Weismann's cytological speculations. Being committed to a dynamical and holistic view of the cell, and opposed to a morphological and reductionist view, Bateson did not claim for Mendel the conception of material particles located in the nucleus. Rather, he emphasized the segregation process as an event concerning the whole cell.
In harmony with this holistic view were the terms Bateson introduced: the unit character or rather factor, which was not referable to a part of a chromosome or any other histological element of the cell; the allelomorph or pair of antagonistic characters; the homozygous zygote formed by the union of like gametes; and the heterozygous zygote formed by the union of unlike gametes. Although Bateson was very successful in introducing the new terminology of genetics he was less successful in pointing the new science in the direction of chemistry and away from the cytology of the chromosomes. Nevertheless I suspect that he was right to view Mendel as one who looked to the physical sciences for his models. There are no doubts as to Bateson's persuasion here. Thus in concluding the first of his reports to the Evolution Committee of the Royal Society he commented:
It is reasonable to infer that a science of Stoechiometry will now be created for living things, a science which shall provide an analysis, and an exact determination of their constituents. The units with which that science must deal, we may speak of, for the present, as character-units, the sensible manifestations of physiological units of as yet unknown nature. As the chemist studies the properties of each chemical substance, so must the properties of organisms be studied and their composition determined. (Bateson, 1902, p.159)
VII. Biographical Approaches to Mendel
The early biographical fragments and introductions which accompanied the rediscovery of Mendel's work at the beginning of this century did not lead to a full-scale biography. Such a work came a quarter of a century later from the pen of the Brünn high school teacher, Hugo Iltis. His interest in the work of Mendel dates back to his first encounter with the Versuche as a high school kid in 1899. He began publishing on the subject in 1908. By 1910 sufficient funds had been raised both in the locality and from overseas for the erection of a statue to Mendel in the Klosterplatz. Bateson, Baur, Cuénot, Hagedoorn, Hurst, Lotsy, Nilsson-Ehle, Tschermak and others traveled to Brünn for the unveiling ceremony and gave papers at this the first Festschrift to Mendel. Iltis edited the resulting volume. (Iltis, 1911).
Iltis' original plan for his research was to produce a history of Mendelism. Hindered by the outbreak of war he did not start on the book which became the first biography of Mendel until the war's end. Then he was granted leave from his teaching duties in Brno and, with support from the Czechoslovak Ministry of Education, he began to write. Unfortunately he found that the Mendelian literature was not only expanding rapidly, but was also in a state of flux. Therefore he restricted himself to conveying concisely 'the modern formulation of Gregor Mendel's work and its theoretical and practical effect whilst stressing the historical standpoint.' His aim was to stimulate the reader to probe further into the Mendelian literature. He advised the reader that he was offering his own particular representation of Mendelism and that in evaluating the results of Mendelism he had sought to arrive at his own particular standpoint. And he added:
Although this standpoint, as far as it relates to the doctrine of evolution, deviates in many respects from that of the majority of Mendelians, the author hopes that it will not as a result be judged adversely. (Iltis, 1924, p. vii.)
Believing passionately that the Mendelian theory was in harmony with Darwinism he railed against those who bandied about phrases like 'the deathbed of Darwinism' and the 'crisis in Darwinism'. The occasion for such slogans, he claimed, came as a result of Johannsen's research which had been 'raised high on the wings of Mendelism'. Angrily he continued:
If the "pure line" is actually an elementary species, and constant . . , if neither environment nor selection is able to exert a permanent effect upon it then would LAMARCK and DARWIN equally be discarded, and ARISTOTLE and LINNÉ would return to favour again [kämen zu ihrem Recht]. (Iltis, 1924, 344.)
But the discovery of the widespread phenomenon of mutation and the new researches suggestive of the inheritance of acquired characters had shown the falsity of the doctrine of the pure line. Too long had Mendelism and Darwinism been opposed like thesis and antithesis. Now the call was 'Back to Darwin', and ahead lay a higher and clearer knowledge of life through 'synthesis' of the two doctrines. (Iltis, 1924, p.372.)
Iltis completed his book at the beginning of 1924. Although it had become a biography rather than a comprehensive text on Mendelism, the last 181 pages were given to the shaping of Mendelism. This included such topics as the heredity of sex, the chromosome theory, linkage and crossing-over, the relation of Mendelism to the theory of evolution, and heredity in man. In the latter there was the same attention to eugenic considerations that is commonly found among genetics texts of this period. Meanwhile the celebration of the centenary of Mendel's birth had given the growing international community of Mendelians the occasion to meet in Brno and to re-establish links severed by war. The published proceedings of the event raised Mendel to the status of a national hero of the new Czechoslovak nation. In his thoughtful analysis of Mendel's work, Vladislav Ruzicka drew attention to its strengths and the problems it raised. Indeed, Iltis' defence of Mendel would appear to be in large part a response to the discussions which took place at this centenary. Ruzicka ended his address with the words:
The discovery of Mendelian laws is an immortal exploit. The movement this discovery has brought about can be compared solely to that evoked by Darwinism.
It cannot be doubted that with Purkeyne, Mendel is our greatest genius in science, and I may say that in success Purkeyne is perhaps second to Mendel.
Even if we admit the opinion held by many in these days that ideologically and methodologically Mendelism has been exhausted, I am justified to say and commemorate with gratification and thanks on this particular day: If at present we find ourselves fairly well on the way to further progress, it is possible only because Mendel has prepared the ground for that progress. (Ruzicka, 1925, p.49)
Iltis' biography is a document of its time. The evolutionary synthesis of the 1930s was yet to come, but Iltis glimpsed his own version of a synthesis. True, Bateson was still preaching a radical scepticism concerning the mechanism of evolution; the Dutch botanist, Jan P. Lotsy (1867-1931), had not ceased to champion the theory of species multiplication solely by hybridization. Yet to most biologists the idea of unchanging hereditary units was not acceptable. Recombination without mutation was not considered a viable resource for a self-respecting evolutionist. What Iltis appears to have done was to sense the direction in which the younger Mendelians were moving and at the same time to establish a representation of Mendel which - unlike Ruzicka's - was supportive of that trend. That is to say, Mendel's work provided crucial evidence which, had Darwin known, would have affected the further formulation of Darwin's theory. He would have been keen to check Mendel's work and to modify his own theory as a result. (Iltis, 1932, p.206)
Strange to relate, the English translation of Iltis' biography was a seriously truncated version of the German original, the latter being 1.7 times the length of the former. This was achieved by leaving out of the translation the whole section on the construction [Ausgestaltung] of Mendelism. In his forward to the translation Iltis made no reference to this. Instead the German foreword was translated minus the paragraph which referred to the missing section of the book. Iltis' 'Darwinian Mendel' was our only source, and became firmly established. R.A. Fisher consolidated this picture more firmly in 1936 with his highly influential paper 'Has Mendel's work been rediscovered?'
Bateson had presented Mendel as a supporter of transformism, but that did not entail his acceptance of natural selection. Iltis glossed over this difference. The formidable British statistician and convinced Darwinian, R.A.Fisher, on the other hand, directly confronted Bateson's view. Writing at a time when geneticists and Darwinians had arrived at a synthesis, Fisher was keen to present Mendel as a covert contributor to the Darwinian theory. Although couched in cautious phrases, Fisher's intent here is implied more than stated. Thus Mendel's rejection of the well-known belief among nineteenth century biologists, that changed conditions of life cause variation, is seen as a response to Darwin. 'The reflection of Darwin's thought is unmistakable,' he declared. (Fisher, 1936, S&S, p.167) But as we know, all Mendel's predecessors in plant hybridization had supported this alleged effect of changed conditions of life, and the evidence of Mendel's 1865 paper as a whole is that it was a critical evaluation of their work - Kölreuter's and Gärtner's names are specifically mentioned, but not Darwin's. As for Mendel, we know just how negative were Mendel's annotations in the Monastery copies of Darwin's books. These were first described by a resident of Brünn, Oswald Richter, in a lecture delivered in 1940. (Richter, 1941)
Richter's view of Mendel was directly opposed to that of Iltis, hence the title of his book: Johann Gregor Mendel, wie er wirklich war. ('Mendel as he really was') (Richter, 1943). His standpoint was that of an opponent of Darwin, who found in Mendel's work evidence of an anti-Darwinian position. Being a convinced theist, Richter judged that the onus of proof was on those who claimed that Mendel was a cryptic doubter, rather than on those who accepted the genuine character of his faith. He pointedly enumerated all the passages in the Monastery copy of The Origin of Species , marked by Mendel, in which Darwin cited the writings of supporters of the creation hypothesis. Was this not because Mendel identified with those very authorities whom Darwin was criticizing? And what justification was there, asked Richter, for the assumption running right through Iltis' biography that Mendel was a 'freethinking' priest? To persuade the reader to reject this idea Richter assembled a host of passages from Iltis' book which attest to the genuine character of Mendel's faith and his calling to the priesthood. (Richter, 1943, pp.135-140)
Although we may feel that Richter went too far in the opposite direction from Iltis, his point of view does deserve attention. How much have we been unconsciously allying Mendel with our own perspective because we want him on our side? Would it not have been reasonable for Mendel to have accepted some form of planned evolution, based on a law-following process the results of which could be predicted, and which God knew in advance? Of course, we will never know whether or not that was the case, but we should at least entertain the possibility when we try to interpret Mendel's work. Fortunately attempts have been made to revise the received view. These we owe to J. Heimans, late professor of botany in Amsterdam, and L.A. Callender, who summarized the conclusions of his thesis study of Mendel's researches in 1988.
VIII. Mendel no Mendelian?
Stimulated by the work of Heimans and Callender, I attempted to bring together the evidence in support of a revisionist interpretation of Mendel's work in 1979 and again in 1985. According to this view Mendel was not a Mendelian if that term is defined as one who explicitly supports 'the existence of a finite number of hereditary elements which in the simplest case is two per hereditary trait, only one of which may enter one germ cell.' The text continued:
On the other hand, if by Mendelian we mean one who treats hereditary transmission in terms of independent character-pairs, and the statistical relations of hybrid progeny as approximations to the combinatorial series, then Mendel surely was a Mendelian. (Olby, 1979, p.254)
This sentence has been ignored by many of those who have criticized this paper. Thus Ernst Mayr wrote with mischievous irony how it was that although none of the rediscoverers questioned Mendel's priority 'this "honour" was reserved for historians. Olby (1979) has recently suggested that "Mendel was no Mendelian".' He omitted the question mark in his citation of the title and went on to suggest that because the word Elemente appears ten times in the paper, 'Evidently they [the elements] correspond reasonably well to what we would now call genes.' (Mayr, 1982, p.716) There follows a laudable discussion of Mendel's contribution in which the alternative definition of Mendelian cited above is apparently accepted. This view of Mendel's contribution is more than supported in the useful commentary provided recently by Alain Corcos and Floyd Monaghan. They go further and, after asserting that Mendel should not be considered the founder of genetics, they praise his merits as 'a great scientist, a pioneer in integrating ideas across three disciplines - botany, physics, and mathematics.' (Corcos & Monaghan, 1993, p.xvi) They have, it seems, taken away the question mark from the question 'Mendel no Mendelian?'
Corcos and Monaghan accept the suggestion that we should interpret Mendel's paper in the context of the questions of his day concerning hybrids, but strangely they do not follow this through when they come to comment on the final section 'Concluding Remarks'. There they fail to check Mendel's reportage of the work of Wichura against Wichura's own publications, and they leave the reader with the impression that Mendel reluctantly allowed for the possibility that constant hybrids do exist, even although he was strongly inclined to doubt it. It was the authority of the supporters of constant hybrids against Mendel's locally circumscribed reputation, that drove him to accept 'their observations at face value,' wrote Corcos and Monaghan and they add: 'since Mendel's time we have discovered that Wichura's hybrids were not true-breeding.' How ironical that Mendel's misrepresentation of Wichura's results has been their source rather than Wichura's own reports! There has thus been a reluctance to accept that Mendel was seriously considering the possibility of the existence of constant hybrids and their potentiality for species formation, although he specifically introduced an alternative form of hybrid reproduction to account for them, and went on to pursue a genus (Hieracium) in which such a process seemed likely to be present.
In his book The Social Basis of Scientific Discovery the American sociologist, Augustin Brannigan, applied his 'attributional' model of discovery to Mendel's achievement. According to this model the status of discoverer is attributed to a named person or persons by society. The process which leads to this result is a social one. Thus among several candidates for the title, Discoverer of America, a consensus was achieved to bestow that honor upon Columbus whilst adopting Americo Vespucci's name for the continent. Although Columbus was not aware that he was landing on a new continent, his successors were. We tend now to think of Columbus as having realized what he was doing! In a similar manner Mendel's rediscoverers agreed that Mendel had already discovered what they found in 1900. Now in its day Mendel's work was known and was treated as a contribution to the normal science of that time - a contribution to the evidence for the strength of reversion. Only in a different context and three decades later was it seen as a major novelty deserving the status of discovery. In 1900 it could receive such a status because it could be fitted into the new perspective of the discontinuity of variation, which Bateson and de Vries recognized as nature's mechanism for preventing the dilution and loss (by crossing) of the variability necessary for evolution to occur. Let us admit that Mendel completed a set of experiments relating to the question of the role of hybrids in the multiplication of species. In 1900 his results could be adapted to solve other important questions , and in this context they were judged to merit the status of discovery. (Brannigan, 1981)
This sociological approach brought Brannigan independently to the same conclusion as Callender regarding the focus of Mendel's research on the question of species multiplication. But is there not more to discovery than attribution? Those who have had the experience of making a discovery know that there is a psychological element in the process, unless it is entirely serendipitous, which makes us act in a positive fashion. We announce it if we are sufficiently confident about it, or we are secretive until we have more evidence. Society may persuade us that we are mistaken or that we are correct. I find it plausible that Mendel considered he had discovered a potentially major principle in biology just as much as Quetelet or Galton thought they had. The major difference was that their work was well known and won the status of discovery at the time, whereas Mendel's was not sufficiently well known to be considered. Granted his work was about species multiplication, it was in the process of investigating this phenomenon that he rightly considered he had made a discovery concerning the transmission of hereditary traits in hybrids (see also Sapp, 1990).
IX The Baptism of Genetics
The term "genetics' was first used by Bateson in 1905 in a letter to the Cambridge zoologist, Adam Sedgwick, and again in 1906, in a public setting. He was delivering the inaugural address at the the third international conference on hybridization for which event he was the president. Explaining to the uninitiated what the Mendelian hybridists were doing had proved difficult and cumbrous, he remarked, yet the new science born of Mendel's work was still nameless. Therefore he offered the conference the term 'Genetics', which he said:
. . . sufficiently indicates that our labours are devoted to the elucidation of the phenomena of heredity and variation: in other words, to the physiology of descent, with implied bearing on the theoretical problems of the evolutionist and systematist, and applications to the practical problems of breeders, whether of animals or plants. (Bateson, 1906, p.91)
This rather wordy definition betrays its author's allegiances; by 'the physiology of descent' he was signaling the experimental tradition as practised by physiologists in contrast to the descriptive tradition of the Darwinian zoologists. His reference to the practical breeders was not just a sop to the members of the society he was addressing, but expressed his recognition of the value of the empirical tradition of hybridization or cross-breeding.
It is customary to draw attention to the links between eugenics and the rise of genetics. Important though those links were, the context in which the subject became institutionalized -- at least in Britain -- was initially that of horticulture and agriculture. In America, as Barbara Kimmelman has shown, agriculture was the dominant host to genetic research in its early days. (Kimmelman, 1992, Paul & Kimmelman, 1988) Horticulture was a growing industry in Britain and the progress of the profession of horticulture was nurtured in the Royal Horticultural Society. This was no pressure group of middle-class activists, but a prestigious and influential organization with a membership of 10,000 in 1906. It served the needs of both the wealthy and aristocratic landowners great and small, and those of the nurserymen and plant breeders in the commercial world. But more than this its Council had recently recognized the potential of hybridization to create new varieties. Instead, therefore, of continuing to concentrate its resources in support of the plant collectors, it turned the Society's attention to hybridization, formed a Scientific Committee, and held the first international conference on the subject in 1899. It was indeed fortuitous that this policy was in place when Bateson first learned of Mendel. New varieties of begonias, sweet peas, amaryllis, lilies, roses and fruit, were furnished from the hands of the breeders, and as for orchids, between 1860 and 1898 the number of new hybrids bred and brought into flower increased from 4 to 800.
The result of Bateson's action in coining the term 'Genetics' was that the Society's secretary, the Rev. W. Wilks, substituted it for the original title - International Conference on Hybridisation and Plant Breeding - when he edited the proceedings for publication. He linked the conference with Mendelism by including full-page photos of Mendel, the Altbrünn Monastery, and a sample of Mendel's letters to Nägeli followed by a five-page account of Mendel's life and work. Thus, notwithstanding the growing interest in the proposals and doctrines of the eugenicists at this time, it was this powerful and prestigious society that gave both national and international recognition to genetics. Retrospectively the first (1899) and second (1902) international conferences on plant hybridization became the first and second international conferences on genetics, and were treated as congresses in periodical literature. Contrast with this the subject of biochemistry, the first international congress of which did not take place until 1949!
When we compare the reception of Mendelian heredity by the horticultural and agricultural communities with its reception by academic botany and zoology, we find a sharp contrast. In 1905 the international congress of botany assembled in Vienna, and as we might expect, Erich Tschermak spoke on his Mendelian research (Tschermak, 1906); but, his was a lonely voice, and at the subsequent event in Bruxelles five years later Mendelism was not even mentioned. True, the zoologists were more forthcoming and at their seventh congress held in 1907, Lucien Cuénot received the prize of Emperor Nicholas II for his essay on "New experimental researches on the question of hybrids.' (Cuénot, 1907) Perhaps they made this award reluctantly - his was the only essay submitted for the prize on time! A hint of the choice which they would have preferred to make is offered by their action in publishing, alongside Cuénot's essay, the essay of Max Standfuss on the inheritance of acquired characters, which had arrived too late for consideration. (Standfuss, 1907) Mendelism did make contact with the interests of the members of this congress, however, in the section on cytology and heredity.
Through the work of Jan Sapp (Sapp, 1983, Sapp, 1987) we have been made aware of the struggle the early geneticists had with embryologists and systematists in their efforts to win authority for their subject, and also the concern they had that the Danish botanist, Wilhelm Johannsen (1857-1927), and the American botanist, Daniel T. McDougall (1865-1958), had over-stepped the mark in their aggressive promotion of the subject. (Kingsland, 1991) While Bateson derided the Darwinians and biometricians in Britain with his own brand of scornful invective, Johannsen challenged biometricians, Darwinians, and the followers of August Weismann with his penetrating redefinition of heredity, spiced with some scorn. The hallmark of Johannsen's contribution was the introduction of new terms with the deliberate aim of banishing what he regarded as the many erroneous associations which old terms carried. Thus the term germplasm had a Weismannian context, and that was a 'purely speculative morphological view of heredity without any suggestive value.' The whole 'transmission conception' of heredity, too, had to be discarded for he warned that no profound insight into the biological problem of heredity would be gained this way. Just as the conception of phlogiston was diametrically opposed to the chemical reality, so was the transmission conception to the biological reality. We should escape these 'splinters of inadequate ideas' he declared:
Therefore I have proposed the words "gene" and "genotype" and some further terms, as "phenotype" and "biotype" to be used in the science of genetics. The "gene" is nothing but a very applicable little word, easily combined with others, and hence it may be useful as an expression for the "unit factors", "elements" or "allelomorphs" in the gametes, demonstrated by modern Mendelian researches. A "genotype" is the sum total of all the "genes" in a gamete or zygote. . . . As to the nature of the "genes", it is as yet of no value to propose any hypothesis; but that the notion of the "gene" covers a reality is evident in Mendelism. The Mendelian workers have the great merit of being prudent in their speculations. In full accordance with this restraint - a quite natural reaction against the morphologico-phantastical speculations of the Weismann school - it may be emphatically recommended to use the adjectival term "genotypical" instead of the noun "genotype". (Johannsen, 1911, pp.132-134)
Johannsen did not mince his words. Heredity, he declared, 'is a mystical expression for a fiction. The ancestral influences are the "ghosts" in genetics, but generally the belief in ghosts is still powerful.' But what of the 'pure line'? This, he asserted, 'is a purely genealogical term, indicating nothing as to the qualities of the individuals in question.' It was comprised of the descendants from a single homozygous organism.
Thus did Bateson and Johannsen as the architects of the new science of genetics formulate their subject. They sought to distance it from embryology and cytology, and to relate it strictly to the genealogical data of Mendelian experimentation. But they failed to immunize it from the developing theory of the chromosome cycle. This first decade of Mendelism, in which its claim to disciplinary status was expressed in so stark a form, came to an end somewhat abruptly in the second decade with the invasion of this plant-oriented discipline by the fruit fly, and the ensuing formulation of the chromosome theory of heredity beginning in 1913.
The aim of this essay has been to impress the reader with the contrasting representations of Mendel's work that are to be found in the literature and to suggest reasons for this situation. These concern historiographical approaches and the particular contexts in which the authors wrote. It has also been the aim of this essay to draw attention to the very distinctive character of Mendelism as it was portrayed by its chief architects - Bateson and Johannsen - in the first decade of this century. In their favor we should grant that they perceived the power of the Mendelian experiment to investigate the nature of heredity and variation. Indeed, Bateson sought to use it to probe developmental questions in his work on plant chimeras. Their scorn of cytological approaches was allied to their fierce rejection of ancestrian conceptions of heredity. It was not simply that Weismann and the Weismannians were indulging in speculations. They used cytological theory in support of the ancestrian doctrine and they supported the omnipotence of natural selection. The resistance of Bateson to the invoking of chromosomal parallels with genes is a remarkable example of opposition to what Lindley Darden calls 'interfield theories' (Darden, 1991).
It is ironical that, although the Drosophila group led by Morgan brought together chromosome cytology and Mendelism, its members belatedly took up the link which Bateson so strongly supported - that of Mendelism with chemistry. The chromosome theory of heredity proving so successful, the temptation to keep to the manipulation of the Mendelian algorithms, this time enriched with the data of crossing-over and linkage, proved too appealing, and the biochemical genetics of insect pigments too difficult. Thus for different reasons, Bateson and Morgan did not pursue each others' versions of inter-disciplinary research. For Bateson, chromosome cytology relied on suspect methods and doubtful interpretations. What was genuine and what was artifact could not be clearly established. For Morgan, on the other hand, the chemistry of genetics in Drosophila proved too difficult. A new organism had first to be introduced. In the history of genetics there is thus good material for pursuing the question of the right organisms for the job. (Clarke and Fujimura, 1992, Kohler, 1994)
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--------, 1906. "The Progress of Genetic Research." Report of the Third International Conference on Genetics; Hybridisation (The Cross-breeding of Genera or Species), The Cross-breeding of Varieties, and General Plant-breeding. London: Royal Horticultural Society, pp.90-97. [published 1907]
Bateson William & R.C. Punnett. 1911. "On Gametic Series Involving Reduplication of Certain Terms." Verhandlungen des naturforschenden Vereines in Brünn 49: 324-344.
Brannigan, Augustin. 1981. The Social Basis of Scientific Discovery. Cambridge: Cambridge University Press.
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Clarke, Adele E., & Joan H. Fujimura (Eds.). 1992. The Right Tools for the Job. A Work in Twentieth-century Life Sciences. Princeton: Princeton University Press.
Corcos, Alain & Floyd V. Monaghan. 1992. Gregor Mendel's Experiments on Plant Hybrids. A Guided Study. New Brunswick, New Jersey: Rutgers University Press.
Cuénot, Lucien. 1907. "New Experimental Researches on the Questions of Hybrids." Seventh Inter. congr. Zoology., pp.99-110
Darden, L. 1991. Theory Change in Science; Strategies from Mendelian Genetics. New York: Oxford University Press.
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