Review Endeavour Vol.27 No.2 June 2003 63

Mendel and modern : the legacy for today

Garland E. Allen

Department of , Washington University, St Louis, MO 63130, USA

The legacy of Mendel’s pioneering studies of hybridiz- offered for his breeding data seemed reminiscent of so ation in the pea continues to influence the way we many of the speculative, particulate theories of understand modern genetics. But what sort of picture that had abounded in the post-Darwinian era, including did Mendel himself have of his work and its ultimate Darwin’s own ‘provisional hypothesis of pangenesis’, uses, and how does that picture compare with the col- August Weismannn’s elaborate theory of ‘ids, idants and lection of ideas and methodologies that was put for- biophors’, ’s imaginary ‘plastidules’, and ward in his name and later became known as ’ postulated ‘pangenes’. Consequently, to ‘Mendelism’? With genetics standing at the center of some, at least, Mendel’s work seemed like just one more of our present biomedical and biotechnological research, the sort of abstract proposals they had encountered all too an examination of the history of our concepts in the frequently. In point of fact the paper probably seemed field can help us better understand what we should and extraordinarily dense, with no illustrations but numerous should not expect from current genetic claims. For that binomial expansions, which were likely to have been a put- enterprise there is no better starting place than Mendel off for many biologists who at the time were notoriously himself. math-shy. For whatever reason, for the first decade of its re-emergence into the scientific world, Mendel’s contri- As we celebrate 50 years of the Watson–Crick model of bution remained controversial at best, dismissed by DNA, it is worth stepping back to take a longer look at the significant sections of the biological community at worst. work that started it all: the pioneering hybridization What ultimately served to establish Mendelism on more studies of the pea (Pisum sativum) and bean (Phaesolus) firm ground between 1900 and 1915 was: (1) its extension by Gregor Johann Mendel (1822–1884) (Fig. 1). Although to an increasingly wide variety of organisms; and (2) its Mendel’s work was first presented at a meeting of the unification with the cytological work on Bru¨ nn Society in 1865, and published in carried out principally through the work of Thomas Hunt its Proceedings in 1866, it received only a modicum of Morgan (1866–1945) and his young, enthusiastic team of attention until 1900, when it was more or less simul- investigators at Columbia University between 1911 and taneously rediscovered by three different investigators: 1925. The work of the Morgan school demonstrated that (1864–1933) in Germany, Hugo De Vries the abstract elements or ‘factors’ discussed by early 20th- (1848–1935) in the Netherlands, and Erich von Tscher- century Mendelians could be regarded as discrete, mak-Szeneygg (1871–1962) in Austria. Whilst all three material units arranged linearly along the chromosomes, found Mendel’s work suggestive, it is not clear that any of them really saw the significance of what he had done, and none of the ‘rediscoverers’ became a major promoter of the new genetics [1]. The first major publicist for Mendel’s work was (1865–1926) in England. Through the Royal Horticultural Society, Bateson had Mendel’s paper trans- lated into English for the first time, and wrote a general exposition that laid out the basic principles of what soon came to be known as ‘Mendelism’ [2]. Bateson’s work brought Mendel to the attention of numerous workers in England, Scandinavia and the United States, in particular to many of those involved in practical animal and plant breeding [3]. Although there was reluctance in some quarters to embrace Mendel’s work immediately – Fig. 1. Gregor Johann Mendel (standing, second from right) with members of the especially among academic biologists – by the end of the Augustinian monastery of StThomas in Brno in about 1862. Mendel can be seen first decade of the 20th century, the theory had gained a observing a plant specimen. Others in the photograph of particular importance in Mendel’s life are the Abbot Cyrill Napp (seated, second from right) and Matous considerable following. However, the explanation Mendel Kla´ cel (seated, first from right), who was also interested in natural science and philosophy, and with whom Mendel had frequent lively discussions. Reproduced, Corresponding author: Garland E. Allen ([email protected]). with permission, from [5], p. 212. http://ende.trends.com 0160-9327/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0160-9327(03)00065-6 64 Review Endeavour Vol.27 No.2 June 2003

the sort of picture Mendel himself envisaged. Second, as an Box 1. The common picture of Mendelian theory introduction to the study of genetics, it has led to † Mendel observed the inheritance patterns of traits or character- unfortunate and now long-entrenched misunderstandings istics in pea plants, such as height, pod color and or seed shape, of how really function, and the relationship between each of which showed alternate forms: tall/short, yellow/green genes and the development of adult traits that has carried and smooth/wrinkled, respectively. over into . † Mendel referred to these alternate conditions as dominant and recessive. † Mendel hypothesized that each trait was represented in the germ Mendel’s background cells of adult plants by two determinants (referred to in his paper Mendel was born on 22 July 1822, in the small rural village as ‘Anlagen’ or ‘elements’), one received from each parent; these of Hyncice, in Moravian Silesia, then part of the Austro– determinants were symbolized by Mendel with a capital letter for Hungarian Empire. As the only son of a peasant farmer, he the dominant form (e.g. A) and a lower-case letter for the recessive was expected to follow in his father’s footsteps and take up form (e.g. a). † The determinants could be combined in one of three ways: two farming. But early on, his interest in natural history and dominants (AA), two recessives (aa) or a dominant and a his studious ways brought him to the attention of the recessive, or (Aa). priest, Friar Schreiber and the local schoolteacher. In spite † Although he knew nothing about the cytology of chromosomes, of financial hardship for his family, young Johann was sent Mendel hypothesized that in the formation of the pollen or , the two factors for each trait would separate and go into to a larger school in a nearby village and eventually different gametes; thus a parent that was pure dominant would qualified for Gymnasium in Opava (Troppau). It was a produce gametes all of which contained the dominant factor (A), period of extreme privation, but Mendel managed to and a parent that was pure recessive would produce gametes all of graduate in 1840 with considerable academic success. One which contained the recessive factor (a); hybrid parents, however, of the chief influences on him at the time were Schreiber’s would produce two kinds of gametes: 50% would contain the dominant factor (A) and 50% the recessive factor (a). Enlightenment ideals, particularly his emphasis on † At fertilization, the double-determinant condition would be science as a way of dispelling superstition and ignorance. restored. Schreiber was keenly interested in applying scientific † If both parents were hybrids, any of the three possible combi- principles to improve humanity, and was heavily involved nations could occur and would be distributed randomly, accord- with local agricultural groups and the Pomological ing to the laws of probability: 1 AA:2Aa: 1 aa; because organisms that are Aa and AA look alike, the ratio based on appearance of the Society [5]. traits (what later came to be called ‘phenotype’) would be 3:1. Financial problems continued to Mendel as he † When two or more characteristics (e.g. Aa, Tt) are followed in a tried to continue his studies at the Philosophy Institute in , the two sets of determinants segregate randomly, Olomuc (Olmu¨ tz). After several periods of illness, brought so that any combination of A, a, T and t is possible, what came to be on it is thought by his poverty and overwork, Mendel known as the principle of random assortment. † Factors somehow determine traits, so that after the term ‘’ managed to finish his studies at the Institute and entered was introduced in 1909, it was common to speak of a ‘gene for Olomuc University. Here, according to records, he took a tallness’ or a ‘gene for wrinkled seed’. During the early years of the course of lectures in physics, mathematics and logic. Mendelian theory, this was referred to as the ‘unit–character’ However, unable to complete his degree owing to financial hypothesis. † Factors are not modified by being combined with their alternate constraints, he applied for, and was accepted into, the form; thus, the factor, t, for shortness is not affected in any way by Augustinian monastery of St Thomas at Brno (then being combined with the dominant factor, T, for tallness in the Bru¨ nn), Moravia in 1843 (Fig. 2). Although he did not hybrid, a concept that became known as the concept of the ‘purity feel a particularly fervent spiritual calling, Mendel of the gametes’. realized shortly after joining the monastery that at last he was free from constant financial worries and could pursue his intellectual interests in exchange for attending and that observed variations in the patterns of inheritance to pastoral duties. of traits could be traced to the mechanics of The monastery at Brno was a center of learning in the behavior during meiosis (gamete formation). Mendel’s early- and mid-19th century, especially in the natural factors (after 1909 referred to as ‘genes’) thus seemed to be sciences and agriculture [6]. The practical and economic real, material units, not metaphysical postulates. In benefits of promoting new agricultural practices was recognition of this work, Morgan was awarded the first among the monastery’s top priorities, with most of its ever for research in genetics in 1933 [4]. income coming from extensive landholdings leased to local Therefore, a common picture of Mendelian theory has farmers. At the time that Mendel entered St Thomas, emerged from this early work and has been promoted in the Abbott (administrator) was Friar F. Cyril Napp textbooks ever since (Box 1). (1792–1867), an enthusiastic naturalist, member of This scheme has made for a very heuristic pedagogy, several local agricultural and scientific societies, and and has been replicated in an almost infinite number of author of many technical papers, particularly on plant high-school and college biology textbooks. Although it has pests. In 1830, he had given over one part of the monastery enjoyed a certain intellectual neatness, this formulation garden to another monk, Matous Kla´cel (1808–1882) for has several problems that have now begun to surface as experimental cultivation of rare Moravian plants. The molecular genetics has provided a far more sophisticated monastery also had an extensive library containing a understanding of gene function than was available in the variety of scholarly texts (Fig. 2). first half of the 20th century. The first problem is simply The importance of agricultural concerns in Mendel’s historical: it is not clear that the neat textbook scheme is developing interests in the natural sciences is clear [7].At http://ende.trends.com Review Endeavour Vol.27 No.2 June 2003 65

Fig. 2. The main church and monastery building (left) that became the seat of the Augustinian Order in 1783, and the magnificent library of the monastery (right), sub- sequently the Mendelianum, a division of the Moravian Museum. One of Mendel’s early mentors in the monastery was Matthew Kla´ cel, who became, after demotion from position of teacher because of his radical ideas, the monastery’s librarian. The library has many works on agriculture, including Liebig’s 1844 Agricultural Chemistry, and Mendel’s copy of the 1860 German edition of Darwin’s . Reproduced, with permission, from [5], p. 46. the time, the amount of experimental breeding in Moravia, Mendel was not a Mendelian in any modern senses of both with plants and animals, was extensive. Indeed, the term, and that proponents of Mendelism, from Bateson Bru¨ nn Natural History Society, before which Mendel read onward, had read much into Mendel’s work that was not his Pisum paper in 1865, was a section of the larger Bru¨nn part of his original formulation. Similar re-evaluations Agricultural Society. The peas with which Mendel worked have subsequently been offered by others [9–11]. were derived from major edible strains, suggesting the The gist of these various reinterpretations is that: close connection between his studies on hybridization and (1) the primary motivation for Mendel’s work was not to agricultural interests. Mendel clearly benefited from the develop a generalized theory of heredity, but was far more monastery’s support of science, and the emphasis placed immediate and practical – to establish patterns of on agriculture by local agriculturalists and members of the hybridization that would have been of interest to agricul- monastery staff turned Mendel’s interests in a specific tural breeders and others in 19th-century Moravia; and direction that ultimately led to his extensive series of (2) Mendel never proposed that there were material breeding experiments. particles, ‘factors’ or ‘Anlagen’, in the germ cells, or that such particles were necessarily transmitted via pollen and Motivation for Mendel’s Pisum experiments egg cells to the offspring. Mendel, they argue, remained It was during his period as a teacher at the newly opened far more agnostic about the physical basis of inheritance Realschule that Mendel began his systematic breeding than later ‘Mendelians’ assumed. experiments with Pisum. One of the major reasons that Indeed, it is much more likely that the direction of has been put forward to explain why a clergyman and Mendel’s hybridization research was guided by the strong schoolteacher would have undertaken such an unusual agricultural interests around him. It was precisely investigation is that he wanted to provide a generalized through hybridization that breeders hoped to generate theory of heredity that would complement Darwin’s theory new combinations of characters that they could exploit to of natural selection (or, as several authors have also form new breeds. The problem was that most hybrids do suggested, to counter Darwin’s theory by demonstrating not breed true and have a tendency to revert to their the fixity of species limits during hybridization). Darwin’s original parental types. What Mendel was able to explain theory had encountered considerable theoretical difficul- were the conditions under which that happened, and most ties because of the prevailing belief by naturalists and importantly, the methods for distinguishing between breeders (including Darwin himself) in ‘blending inheri- hybrids and true-breeding forms that might look pheno- tance’ – the idea that any trait in the offspring was a typically similar. Crucially, his hypothesis of dominant and ‘blend’ of the traits observed in the two parents. Thus, if recessive characters provided an alternative to ‘blending parental differences blended in the offspring, new vari- inheritance’. Whatever happened within the germ cells of ations would be diluted in every generation, leaving little the hybrids, the characters were not blended by residing for natural selection to act on. However, it is clear that together. This became as important a principle for breeders Darwin’s work could not have been Mendel’s initial as it would become later for Darwinian evolutionists, motivation, because he had already begun his experiments because it freed both groups from the loss of distinct in 1856, three years before the publication of The variations through blending or ‘swamping’ in the hybrid. Origin of Species. Nevertheless, it is not possible to be interested in If not , what was the initial motivation for hybridization without simultaneously being drawn into Mendel, and what did his paper say, both to his accepting, however loosely, some concept of heredity. contemporaries and to those who read him after the Hybridization involves mixing germ lines from two ‘rediscovery’ in 1900? In 1979, Robert Olby revised our different ancestries, and how those germ lines interact, understanding of the Pisum paper by stripping it of its by definition, forms a theory of heredity. Thus, to claim 20th-century interpretations [8]. He concluded that that Mendel was interested only in hybridization and not http://ende.trends.com 66 Review Endeavour Vol.27 No.2 June 2003 in any general principles of heredity is to make a confusing constant emphasis on ‘characters’, his recognition that it distinction. The two processes are not only not mutually was sometimes difficult to determine in what character exclusive, they are complementary. The revisionist view class an individual should be placed, and his meticulous therefore is that Mendel’s major motivation (and interest) record-keeping all testify to his strongly empirical and no- lay in establishing principles of hybridization, and not in nonsense approach to experimentation. establishing a generalized theory of heredity as was assumed by his early-20th century followers. Mendelism and the ‘unit–character’ hypothesis These re-interpretations of Mendel also argue that By the time Mendel’s paper was rediscovered in 1900 and nowhere does he explicitly state that the germ cells contain had begun to receive attention from biologists and particles that determine the character of a trait. Mendel’s breeders in industrialized countries, economic, social and symbols (e.g. T,t and A,a), they argue, were merely intellectual conditions were significantly different than algebraic notations and were never meant to represent those in 1866 Central Europe. The industrial revolution in material entities in any biological sense. It is true that Europe and the US had placed many new demands on Mendel is not explicit on this matter. He talks in his paper agriculture [13]. Not only were there increasing demands about alternate characters (tall and short) segregating in on food production to supply the large urban workforces the germ cell of the hybrid parent, but he does not refer to that had developed in industrial areas, but much of that determiners or particles; moreover, he does not talk about workforce had come from the agricultural sector, leaving it segregation of the two characters in the homozygous in short labor-supply. Mechanization of agriculture had forms, and represents homozygotes symbolically with only proceeded with great rapidity at the end of the 19th a single letter (such as A for the dominant parent or a for century, a process that had initiated what has been called the recessive), whereas he always represents the hybrids the ‘industrialization of agriculture’ [14]. During the with two letters (e.g. Aa). Thus, he consistently shows the second half of the 19th century, scientific agriculture results of a as A þ 2Aa þ a. based on the organic and physiological chemistry of Justus A careful re-reading of the Pisum paper suggests that von Liebig (1803–1873) and his school in Giessen had Mendel was ambiguous, but not explicitly agnostic, greatly improved yields by attention to aspects such as towards the notion of hereditary particles. The ambiguity fertilizers and animal and plant nutrition. But by 1900, arises because throughout his paper, Mendel consistently those inputs had, for the time, achieved their technical talks about the ‘characters’ [Charactere ] of the parents or limits. Improvements in breeding higher-yielding varieties, offspring of his crosses, which of course refer to the visible however, held out a wholly new potential. adult traits. His empiricism and training in the physical One aspect of agriculture – husbandry – was still in a sciences led him to emphasize what he could see in the rudimentary stage at the turn of the 20th century. Most plants he was breeding. At the same time, toward the end animal and plant breeders operated by various rules of of his paper, Mendel wrote about the implications of his thumb that they had developed their separate localities or experiments for understanding the composition of the had learned and modified from others. It was largely a ‘fertilization cells’ (i.e. pollen and egg). Here, he introduces craft, with no general rules that applied across the board. the terms ‘Anlage’ and ‘Elemente’ in reference to what is The reintroduction of Mendel’s work at this juncture transmitted from parent to offspring through fertilization. generated hope that some principles of heredity might, at ‘The development proceeds from a constant law which is last, provide the breeder with methods that could yield grounded in the material composition and arrangement of more predictable results. Although in reality the appli- the elements [Elemente ], which come together in the cell in cation of Mendelian principles to improving animal and a viable union,’ wrote Mendel [12]. plant productivity turned out to be more difficult than it Indeed, it would have been unusual in Mendel’s day, initially seemed, optimism was nonetheless shown by and given his training, not to at least have thought in many academic biologists, US Department of Agriculture terms of some sort of discrete hereditary particles being (USDA) officials, and breeders in the early decades of the passed from parent to offspring during reproduction. century. The economic and social conditions made Men- Virtually every theory of heredity proposed during the del’s work look profitable in 1910 in a way it had not looked middle and later years of the 19th century was couched in in 1866. particulate terms so that it was common among biologists, But as academics and breeders took up the nascent especially in the German-speaking world, to think in science of Mendelism [15], there remained an uncertainty terms of atom-like particles or molecules as agents of over what was actually transmitted from parent to hereditary transmission. The problem with most of these offspring during fertilization. Although Wilhelm Johann- theories was that they were largely speculative, and based sen (1857–1927), the Swedish plant breeder who coined on a few observations and little, if any, experimental the term ‘gene’, and William Bateson, who coined the term evidence. It is not surprising therefore, that Mendel hints ‘genetics’, both favored a more abstract statistical model of at the existence of such components in the germ cells. the hereditary unit, others, especially in the US, pressed However, it is important to remember that he was first and for a more material, atomistic interpretation from 1903 foremost an empiricist, and was highly restrained when it onward. The abstract ‘element’ of Mendel’s paper had came to speculation about mechanisms. In this sense, quickly become the discrete gene of the rediscovered historians are right who emphasize that Mendel was Mendelism. Textbooks began to present images of primarily interested in establishing the laws of hybridiz- Mendelian crosses using Mendel’s capital and small letters ation rather than a general theory of heredity. His for dominant and recessive traits. http://ende.trends.com Review Endeavour Vol.27 No.2 June 2003 67

Between 1900 and 1910, this interpretation of Mende- just such a conceptual notation as is used in algebra or in lism communicated two important notions to the gener- chemistry’ [18], whilst British polymath J.B.S. Haldane ation of biologists who were beginning to learn about the (1892–1964), as late as the 1930s, claimed that ‘…the new genetics. First, there was no hard-and-fast distinction atomic nature of suggests very between the letter or factor and the adult character for strongly that even where variation is apparently continuous which it stood. Thus, would write about the this appearance is deceptive. On any chemical theory of inheritance of ‘height’ or ‘wing shape’ or ‘red eyes’ as if the the nature of genes this must be so.’ [19] trait itself was what was carried in the male or female The implication that the discreteness of the gene gamete. Furthermore, in the early decades after the implied the organism was constructed as a ‘mosaic’ of rediscovery of Mendelian theory, the identification of the adult traits was given explicit voice by Bateson within the hereditary unit with the adult trait was graphically first years of his encounter with Mendelism. In 1901, he reinforced by the Punnet Square – a method of calculating wrote: Mendelian combinations – which blurred what would In so far as Mendel’s law applies, the conclusion is forced upon us become known after 1911 as the ‘phenotype–genotype’ that the living organism is a complex of characters of which some, distinction, and gave the impression that the inherited at least, are dissociable and are capable of being replaced by factor was the trait in miniature. It was this conflation that others. We thus reach the conception of unit characters, which may led embryologists like the young T.H. Morgan to reject the be rearranged in the formation of reproductive cells [20]. Mendelian hypothesis for a decade [4]. For Morgan and The next year Bateson wrote even more boldly: ‘The others, the Mendelian ‘factor’ or ‘gene’ smacked too much organism is a collection of traits. We can pull out of the embryologists’ old bugbear, (the yellowness and plug in greenness, pull out tallness and idea that the complete adult exists already preformed in plug in dwarfness.’ [21] This mosaic view of the adult the fertilized egg, and that organism parallels the mosaic view of the , and involves only an unfolding or growth of the embryo in thus pictures the organism as an aggregation of inter- size). , the alternative view, had replaced changeable parts that can be arranged and rearranged by preformationism by the mid-19th century, so that Mendel’s assembling the right combination of genes. Admittedly, not work in the form presented by Mendelians, seemed like an all early Mendelian geneticists took quite such a mechani- outdated throwback to a long-discarded idea. cal view of heredity, but Bateson was one of the leaders in With the wedding of Mendelian theory to the cytological the field and among its most vocal proponents. His investigation of chromosomes by Morgan and his group influence was therefore considerable. It is thus even after 1910, the material, discrete and atomistic concept of more ironic that as late as 1922, Bateson still held strong the gene gained considerable prominence. By carefully reservations about linking Mendelian genes to chromo- correlating the inheritance patterns of gene somes [22]. with observable changes in chromosome structure, Mor- The atomistic, mosaic conceptualization of the gene was gan and his students were able to show that genes could be initially fruitful, allowing biologists to develop a quanti- clearly regarded as material entities that occupied specific tative, experimental and predictable aspect of their science positions – loci – linearly arranged along the chromosome. that made it as ‘hard’ as anything in chemistry or physics By 1915, when the group published the their path- [23]. However, it created problems almost from the outset. breaking book, The Mechanism of Mendelian Inheritance It allowed biologists to put aside questions of gene [16] the ‘beads on a string’ model of the chromosome had function, or the relationship between Mendelian genes, become an icon. Not only did this model promote the idea of embryonic development, and even evolution. From 1915 genes as atomistic units, it also further supported, onward, most attention was paid to the mechanics of gene indirectly, the unit–character hypothesis. The gene was shuffling during transmission of chromosomes from parent now viewed not only metaphorically, but also literally as an to offspring. This trend, which marked the hey-day of atom, entering now into this, now into that combination, , led to the extraordinary feat of mapping but emerging each time with its own integrity in the same the chromosomes of several model organisms, such as the fashion as atoms entered into, and came out of, molecular fruitfly, and mouse. But the atomistic trend in combinations. Indeed, the language of chemistry began to classical genetics also left an unfortunate legacy. By enter genetics explicitly in relation to the discreteness of perpetuating the unit–character concept of the gene, the Mendelian factor. Harvard W.E. Castle even with lip-service paid to the idea of gene interactions, (1867–1962) wrote early on that: the vast majority of the public and many biologists as well, all observed inheritance phenomena can be expressed satisfac- still hold to the view that one, or at best a very few, genes torily in terms of genes, which are supposed to be to heredity what determine each specific, adult trait. atoms are to chemistry, the ultimate, indivisible units, which Nowhere is the tendency to attribute discrete gene constitute gametes much as atoms in combination constitute elements to specific traits more common, and perhaps compounds [17]. more socially troublesome, than in the area known as Whilst Castle was arguing that genes were not quite like behavior genetics. To date, social and personality atoms because they could be altered by the selection traits as complex and varying as schizophrenia, manic process, that he mentions the analogy at all indicates depression, alcoholism, criminality, violence, shyness, something of its prevalence. Somewhat earlier his col- homosexuality, risk-taking and religiosity, have all been league E.M. East had written that ‘Mendelism is therefore headlined at one time or another as ‘caused by a gene’. Not http://ende.trends.com 68 Review Endeavour Vol.27 No.2 June 2003 only do such claims greatly oversimplify the biological were really comparable to those obtained by Mendel. See, Corcos, A. process of development, during which genes interact with and Monaghan, F. (1985) Role of de Vries in the recovery of Mendel’s other genes and the environment, they suggest a set of work. J. Hered. 76, 187–190; (1986) Tschermmak: a non-discoverer of Mendelism I: an historical note. J. Hered. 77, 468–469; and (1987) potential solutions that is deceptive: drug therapy, gene Tscheremak: a non-discoverer of Mendelism II: a critique. J. Hered. 78, therapy or sterilization. Indeed, sterilization was 2–10. These various positions have been admirably summarized in implemented in both the US and Germany in the old Peter Bowler (1989) The Mendelian Revolution. The Emergence of movement, when simplistic genetic notions Hereditarian Concepts in Modern Science and Society, Johns Hopkins allowed the compulsory sterilization laws to be passed University Press, especially chapter 1 2 Bateson, W. (1902) Mendel’s Principles of Heredity: A Defense, for those with ‘undesirable’ hereditary conditions [23]. Cambridge University Press, Cambridge, UK Today, Norplant can replace surgical sterilization, and 3 Letter from William Bateson to his wife, Beatrice, 3 October 1902, pharmacogenetics looms on the horizon, promising to quoted in Paul, D. and Kimmelman, B. (1988) Mendel in America: counteract the effects of defective genes and to yield huge theory and practice – 1900–1919. In Rainger, R. et al. (1988) The benefits for the pharmaceutical industry. American Development of Biology, p. 283, University of Pennsylvania Press Genes are of course critical components in one way or 4 Allen, G.E. (1978) , the Man and His Science, another of all of our traits. But because of the increasingly Princeton University Press detailed findings of molecular genetics and the Human 5 Orel, V. (1996) , the First Geneticist, pp. 40–41, Oxford Genome Project, the picture of what genes do and how they University Press function in the development of adult human characters 6 Orel, V. (1973) The scientific milieu in Brno during the era of Mendel’s research, J. Hered. 64, 314–318; see also [5], chapters 2–3 has changed dramatically from the legacy built out of the 7 Orel, V. and Wood, R. (2000) Scientific animal breeding in Moravia early interpretations of Mendel’s work. With his skepti- before and after the rediscovery of Mendel’s theory. Quarterly Review cism about undue speculation regarding the mechanics of of Biology 75: pp. 149–157 the hereditary process, Mendel might indeed have been 8 Olby, R. (1979) Mendel no Mendelian? 17, pp. 53–72 more in tune with modern than with the 9 Brannigan, A. (1979) The reification of Mendel, Social Studies of Mendelians who crafted the classical concept of the gene Science 9, pp. 423–454 10 Meijer, O. (1983) The essence of Mendel’s discovery. In Gregor Mendel in his name. and the Foundation of Genetics (Orel, V. and Matalova, A., eds.), The Mendelianum of the Moravian Museum in Brno, pp. 123–178 Conclusion 11 Monaghan, F.V. and Corcos, A. (1984) On the origins of the Mendelian As we look forward, it is clear that one of the most laws. J. Hered. 75, 67–69; and (1984) The true Mendelian laws. important forefronts of modern genetic research lies in the J. Hered. 75, 321–323 12 Mendel, G., cited in [11], p. 105. The original reads: ‘Diese Entwicklung area of what has been variously called ‘the genetics of erfolgt nach einem constanten Gesetze, welches in der materiellen development’, ‘developmental genetics’, and when com- Beschaffenheit und Anordnung der Elemente begru¨ ndet ist, die in der bined with evolutionary theory, the ‘evolution of develop- Zelle zur lebesnfa¨higen Vereinigung gelangten.’ ment’ or ‘Evo–Devo’ for short. These emerging fields, 13 Allen, G. (2000) The reception of mendelism in the United States, which synthesize the classical genetics of the first half of 1900–1930. Comptes Rendu Academie des Sciences, Paris. Sciences de la vie 323, 1081–1088 the 20th century with the molecular genetics and 14 On the industrialization of agriculture in 20th-century America, see of the second half, promise to yield Shannon, F.A. (1961) The Farmer’s Last Frontier, pp. 362–365 and a more complex, and hopefully more realistic picture of 366–367, Holt, Rinehart and Winston; and Kloppenberg, J.R. (1988) how the genome guides the individual organism from First the Seed. The Political Economy of Plant Biotechnology. Cam- fertilization to adulthood. bridge University Press, especially chapters 2–4 15 Punnett, R. (1911) Mendelism, Macmillan We are standing at a divide between an old and a new 16 Morgan, T.H. et al. (1915) The Mechanism of Mendelian Inheritance, genetics, between a mosaic and mechanical and a holistic Henry Holt & Co. and integrated view of the organism that promises to yield 17 Castle, W.E. (1919) Piebald rats and the theory of genes. Proc. Natl. exciting results in the years ahead. It behoves us to Acad. Sci. U. S. A. 5, 126–130; quotation on p. 127 understand the pathway that has brought us to this 18 East, E.M. (1912) The Mendelian notation as a description of historic juncture, not only so that we may take the fullest physiological facts. Am. Nat. 46, 633–695 19 Haldane, J.B.S. (1932) The Causes of Evolution, p. 57, Harper and advantage of our newest research paths, but also that we Brothers avoid the disastrous social consequences that can arise 20 This quotation comes from Punnett, R.C., ed. (1928) Scientific Papers from misplaced expectations of what genetics can do. Like of William Bateson, (vol. 2), p. 1, Cambridge University Press all other scientific and technological findings, we must first 21 Bateson, W. (1902) Mendel’s Principles of Heredity: A Defense, understand the science itself and its history to recognize Cambridge University Press; quoted from Lewontin, R.C. and Levins, R. (1985) The Dialectical Biologist, p. 180, Harvard University Press both its potential and its limitations. 22 Coleman, W. (1970) Bateson and chromosomes: conservative thought in science, Centaurus 15, 228–314 References 23 For a more detailed discussion of the mechanistic view of the gene, see 1 Sturtevant, A.H. (1965) , Harper & Row; in chapter Allen, G.E. (2002) The classical gene: its nature and its legacy. In 21, Sturtevant reviews the claims that the three rediscoverers were Mutating Concepts, Evolving Disciplines: Genetics, Medicine and really so independent, whilst several papers by Alain Corcos and Floyd Society, (Parker, L.S. et al., eds), pp. 11–41, Kluwer Academic Monaghan suggest that only Correns had really collected data that Publishers

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