Mendel's Opposition to and to Darwin

B. E. Bishop

Although the past decade or so has seen a resurgence of interest in Mendel's role in the origin of genetic theory, only one writer, L. A. Callender (1988), has concluded that Mendel was opposed to evolution. Yet careful scrutiny of Mendel's Pisum pa- per, published in 1866, and of the time and circumstances in which it appeared suggests not only that It Is antievolutlonary In content, but also that it was specif- ically written in contradiction of Darwin's book The Origin of , published in 1859, and that Mendel's and Darwin's theories, the two theories which were united in the 1940s to form the modern synthesis, are completely antithetical.

Mendel does not mention Darwin in his Pi- [Mendel] in so far as they bore on his anal- sum paper (although he does in his letters ysis of the evolutionary role of hybrids." to Nlgeli, the famous Swiss botanist with Olby's (1979) article, entitled "Mendel whom he initiated a correspondence, and No Mendelian?," led to a number of revi- in his Hieracium paper, published In 1870), sionist views of Mendel's work and his in- but he states unambiguously in his intro- tentions, although no agreement has been duction that his objective is to contribute reached. For instance, some writers, un- to the evolution controversy raging at the like de Beer, Olby, and Callender, overlook time: "It requires a good deal of courage or minimize the evolutionary significance indeed to undertake such a far-reaching of Mendel's paper, while others maintain task; however, this seems to be the one that Mendel had little or no interest in he- correct way of finally reaching the solu- redity, an interpretation that has been op- tion to a question whose significance for posed by Hartl and Orel (1992): "We con- the evolutionary history of organic forms clude that Mendel understood very clearly must not be underestimated" (Mendel what his experiments meant for ." 1866). So It is not plausible that Mendel If there is any consensus at all about Men- could have been writing In ignorance of del, it is, quite extraordinarily, that he was Darwin's ideas, which had aroused the an evolutionist, but it is inconceivable that worldwide furor. a priest could have been openly support- Of course, neither Darwin nor Mendel ing a theory that Darwin had been hesi- used the word "evolution." It Is a term tant to publish because of Its heretical re- that came into vogue as a synonym for ligious and political implications. Darwin's "descent with modification" shortly after the publication of The Origin Mendel does not make a definite state- of Species, when it assumed application to ment about his stance, but it is argued fully developed organic forms, In contrast that there is evidence, both from the his- to its earlier embryological connotation. torical background and in Mendel's paper However, has observed that itself, that indicates that the latter was an it is in exactly this sense that Mendel em- ad hoc attempt to refute Darwin's ideas ploys the German expression "Entwick- and that Mendel's position was one of the- lungs-Geschichte," and he comments: ological orthodoxy. (Mendel was a well-in- "Here, therefore, was Mendel, referring to tegrated member of his monastic com- evolution and laying down an experimen- munity and a zealous defender of the faith, tal programme for its study by means of not a dissident.) Furthermore, if Mendel's research in breeding hybrids" (de Beer paper Is seen in this light, the many incon- 1964). Some years later, gruities (or apparent incongruities) that Address reprint requests to the author at 6 Barbados Rd., Federation Park, Port of Spain, Trinidad, Trinidad (1979) also emphasized the evolutionary have been the subject of discussion and Tobago, West Indies. orientation of Mendel's paper: "The laws throughout the twentieth century disap- Journal of Heredity 1996^7^05-213; 0022-1503/96/J5.00 of inheritance were only of concern to him pear.

205 Evidence From the Historical entifically likely, and that the strategy he possessed a copy, and his marginalia and Background really followed must have been complete- notes on the flyleaf suggest that he stud- ly different" (DI Trocchio 1991). Di Troc- ied it in detail several times (Orel 1984). It is known that Mendel possessed a copy chio argues that the numerical data for the Olby (1985) comments: "These notes are of the second German edition of The Ori- mono-, di-, and trlhybrid experiments important because they show Mendel at gin of Species published in 1863, many pas- were obtained by progressively disaggre- work, hunting for clearly-marked charac- sages of which he marked (de Beer 1964; gating those from polyhybrid crosses con- ter differences between the various forms Orel 1971), and his paper distinctly re- ducted for about three genera- of ." flects certain important aspects of Dar- tions, that Mendel may have used the 3:1 There is no record of any previous ex- win's thought, as de Beer (1964) has point- ratio as his criterion for the selection of periments by Mendel that might have led ed out. Also, Mendel was most probably the seven traits, and that he did not report to the initiation of the famous Pisum pro- familiar with the earlier German edition all his data "because he was well aware gram. ["But despite all that has been dis- owned by the society to that other Pisum characters did not follow covered and preserved we have no direct which he belonged (Orel 1971). In 1861, the law, having already ascertained that information on the sources of Mendel's In- the parent body of this society had dis- they produced strange ratios (i.e., that spiration ..." (Olby 1985).] Also, Mendel cussed The Origin, a year after the publi- they were linked)" (Di Trocchio 1991). Di does not provide a time schedule for his cation in a German journal, to which Men- Trocchio adds: "Had he [Mendel] de- experimental program or even state the del could have had access, of the "word- scribed the real course of his experiments date of commencement of the project, ob- by-word translation" of Darwin's chapter he would have had to admit that his law serving in his paper only that it occupied entitled "On the Geological Succession of worked for only a few of the hundreds of "a period of eight years." However, in his Organic Beings," in which Darwin clearly Pisum characters—and it would thus have second letter to Nageli, obviously a defen- formulated his theory of descent with been considered more of an exception sive response to the latter's criticism ["I modification through than a rule" (Di Trocchio 1991). (The pos- am not surprised," Mendel wrote, "to hear (Orel 1971). [Mendel was obviously inter- sibility that Mendel reported marginal to- your honor speak of my experiments with ested in Darwin's ideas. , Men- tals without saying so was first raised by mistrustful caution" (Stern and Sherwood del's first biographer, notes that Mendel Fisher in 1936.) 1966)], Mendel elaborates on several is- bought all Darwin's later works as soon as Therefore, 4 years would have been ad- sues, stating categorically that the exper- they were published in German, adding: equate time for Mendel to perform what- iments were conducted from 1856 to 1863, "... and not Darwin's books alone, for al- ever experiments were necessary and to when "they were terminated in order to most all the Darwinian literature of the write his paper, especially as he was fa- obtain space and time for the growing of 'sixties and 'seventies is to be found in the miliar with the prior work in the field, of other experimental " (Stern and monastery library at Brunn" (Iltis 1932).] which, however, he makes no acknowledg- Sherwood 1966). Nevertheless, through- This would have given Mendel at least 4 ment, although many of the earlier inves- out this period, Mendel maintained a live- years in which to carry out his experi- tigators had also used garden and re- ly correspondence with his brother-in-law, ments and prepare his paper for presen- ported very similar results: "It is well Leopold Schindler, and yet he never allud- tation in February and March 1865. Evi- known that practically all the points ed to his scientific work, although making dently this would not be sufficient time if proved by Mendel in his main paper had frequent references to the events of the the experimental program was conducted been made by others before—J. Goss and day (Iltis 1932). And it is clear from Na- as Mendel records, but recently doubt has A. Seton in 1822 reported the results of geli's reply to Mendel's first letter, with been cast on the veracity of Mendel's ac- their pea-crossing experiments, indicating which Mendel had enclosed his paper, count. Federico Di Trocchio (1991), in an in the first hybrid generation that Nageli considered the latter to be no more than an outline: "I shall not remark article entitled "Mendel's Experiments: A and reappearance of recesslves in the sec- on any other points in your communica- Reinterpretation," observes: "To under- ond. Knight verified their results in 1824, tion, for without a detailed knowledge of stand Mendel's work we are forced to ad- adding such observations as the 'scatter- the experiments on which they are based mit, as was tentatively suggested by Wil- ing' of 'indivisible' characters in the gen- erations following hybridization. [Knight I could only make conjectual comments" liam Bateson, that most of the experi- (quoted by Stubbe 1972). ments described in Versuche are to be con- also reported backcrosses and a 2 year tri- sidered fictitious." Di Trocchio (1991) al period, as Mendel was later to do in his It was in May 1856, when he was pur- claims that Mendel did not perform the paper.] A. Sageret (1826) had further sub- portedly setting out on his experimental seven monohybrid experiments that he re- stantiated the independent reappearance program, that Mendel failed in his second ports, the basis of the law of segregation: of Knight's 'indivisible' characters in suc- attempt to become a certificated teacher, "... Mendel never carried out these ex- cessive generations; only some characters an event that was preceded and followed periments in the garden, but rather only reappeared in all generations (the domi- by illness. Olby (1985) writes: "Evidently on the pages of his notebooks." He sug- nants). This work was known to Mendel Mendel was very ill and it was presumably gests that this could also be true of both when he planned his experiments" (Gedda the same illness which had plagued him at the dihybrid experiment and trihybrtd ex- and Milani-Comparetti 1971). Mendel's at- times of stress when he was a schoolboy periment, from the results of which the tention had been drawn to these papers and a student. Dr. Joseph Sajner, who has law of independent assortment was de- by Gartner's book Experiments and Obser- made a special study of Mendel's Illness, rived, and he states: "... we are to-day vations upon Hybridization in the calls it an 'unstable psychological consti- forced by a series of anomalies and incon- Kingdom, which was published in German tution'. Mendel had already been ill earlier in 1849 and which extensively reviewed in- gruities to admit that Mendel's account of in the year, no doubt owing to the stress vestigations into plant crossing. Mendel his experiments is neither truthful nor sci- of his studies, and when faced with the 'Vi-

206 The Journal erf Heredity 1996:87(3) enna ordeal' again his nerves gave way." So Mendel's fellow must have not "at innumerable periods in the earth's his- [It was in 1856 also that the controversy only understood his work but regarded it tory certain elemental atoms have been over procreation (whether only one par- with great approval, for 2 years after Men- commanded suddenly to flash into living ent or both parents make a material con- del's paper was published they elected tissues," and Darwin's themes were evo- tribution to the embryo), which was the him abbot of the rich and influential mon- lution, population, and heredity, a concep- greatest biological conflict before the Dar- astery to succeed an outstandingly good tual framework that is mirrored in its en- winian revolution, was only just "coming administrator. His priorities necessarily re- tirety by Mendel's paper. ["As a conse- to a head" (Orel 1982).] At that time, Men- aligned, Mendel spent the rest of his quence of his evolutionary approach, del was a supply teacher at Brunn Modern in an office of power and privilege. It was Mendel adopted, as Thoday (1966) has School, which had just recently been a position to which he had aspired. In a correctly pointed out, the method of pop- founded. In 1857 and 1858, Mendel re- letter to his brother-in-law, 4 days before ulation analysis ..." (Mayr 1982).] Hered- ceived commendations from the educa- the election, Mendel had written: "It is still ity was a vital component of Darwin's the- tion authorities for his "zealous and suc- uncertain which of us will be the lucky ory, for he reasoned that for variation to cessful endeavours" (Iltis 1932) in pro- one. Should the choice fall on me, which I be evolutionarily important it must be her- moting the working of the school, and he hardly venture to hope, I shall send you a itable, although he was forced to admit: remained in his office until 1868. Thus, wire on Monday afternoon" (quoted by Il- "The laws governing inheritance are quite Mendel could have had very little time to tis 1932). unknown" (Darwin 1859). Thus, it is high- devote to his botanical pursuits, particu- After becoming spiritual leader of his ly significant that only a few years later larly in the important early stages. monastery, Mendel journeyed to Rome to Mendel elaborated his very definite at- The myth has prevailed that Mendel be received by the Pope (Sootin 1959). In omistic theory of heredity—a theory, worked in isolation, the bibulous gardener 1872, four years after his election, he was moreover, that results only in stasis: "The usually being cited as the only helper and made Commander of the Order of Franz pure process of Mendelian heredity does held responsible for the "too good" re- Joseph, the published citation for the not produce any evolutionary change at sults, but it appears that the experiments award referring not only to Mendel's all: the population stays the same" (Ridley were a communal enterprise, to which the teaching career but also to his political 1985). monastic hierarchy must have been very service (Orel 1984). The populational orientation of Men- kindly disposed to allow such appropria- Some of Mendel's notes for addresses as del's paper is also significant. Population tion of time and space usually set aside for abbot have survived. Zumkeller (1971) thinking was Darwin's most original and other purposes. Abbot Napp, the head of writes: "For precisely because these ser- revolutionary concept, a concept that the monastery, was keenly interested in mon outlines are but little polished, they made the introduction of natural selection natural history, and, like Mendel and other give us a clearer idea of the personal relig- possible (Mayr 1972), and its genesis has monks, he was a member of the agricul- ious sentiment and thought of the preach- been well documented, but it was not until tural society that had discussed The Ori- er. One fact imposes itself at the very first the publication of Darwin's iconoclastic gin of Species in 1861. Orel (1984) ob- reading of these texts: Here speaks a man book that it was unveiled to public view. serves: "Perhaps it is as well that, during of true faith and a pastor who thinks with Therefore, Mendel must have either inde- his studies and early experiments, Mendel the Church. He endeavors zealously to ac- pendently adopted a populational ap- enjoyed both the moral and material sup- quaint his audience with the unadulterat- proach from the outset or planned his ex- port of Abbot Napp, who understood his ed Christian doctrine ... Decades ago, periments with knowledge of Darwin's motivation if anyone did." some writers endeavored to present Men- ideas, for it is obvious from the design of Hugo Iltis, a teacher in Brunn like Men- del as a freethinker, who searched for the reported experimental program that del before him, names two other monks truth 'without deference to dogmas.' It has there could have been no change in his involved in the experimental program and long been recognized that this opinion is research objective after its initiation. refers to a senior member of the staff at incorrect. The discovery of these sermon At that time, the existence of constant the school where Mendel taught, Alexan- outlines of the Abbot Mendel should cut (true-breeding) hybrids, which several ex- der Makowsky, the noted natural historian the ground forever from under such im- perimentalists had reported, was of great "who from 1860 onwards collaborated putations." interest, as Mendel emphasizes in his Pi- with Mendel" (Iltis 1932) (i.e., after the In 1870, there had been a proclamation sum paper: "This feature is of particular publication of The Origin of Species). Ali- of the infallibility of the Pope, and later importance to the evolutionary history of pius Winkelmayer, one of the monks who encyclicals announced the infallibility of plants, because constant hybrids attain assisted Mendel, was Mendel's contem- the Bible. It was not until 1951 (almost a the status of new species" (Mendel 1866; porary, having entered the monastery century after the publication of The Origin emphasis in original). And it was Mendel's soon after Mendel, and he, like several of Species), when Pope Pius XII relaxed the concern with constant hybrids that other monks, had a taste for . For dogmatic interpretation of the Bible, that spurred him to enter the fray again a few instance, Thomas Bratranek and Mat- open discussion of evolution was officially years later with his Hieracium paper: "The thaeus Klacel, two of the monastery's permitted by the (George question of the numerous and constant in- leading scholars, "though not professional 1982). termediate forms has recently acquired no botanists, were distinguished amateurs of small interest since a famous Hieracium that branch of " (Iltis 1932). Cor- specialist has, in the spirit of the Darwin- cos and Monaghan (1990) comment: "His Evidence From Mendel's Paper ian teaching, defended the view that these [Mendel's] colleagues were highly intellec- The Origin of Species was an onslaught on forms are to be regarded as [arising] from tual and, like him, were teachers and mem- the doctrine of special creation, which the transmutation of lost or still-existing bers of learned societies." Darwin (1859) referred to as the belief that species" (Mendel 1870). But Mendel him-

Bishop • MendeTs Opposition to Evolution and to Darwin 207 self does not report constant hybrids in which he enclosed his paper (Stern and law" quantifying reversion (in which the his Pisum paper: "... he [Mendel] did not Sherwood 1966). population reverts to the pure parent find any constant hybrids" (Monaghan The late eighteenth- and early nine- forms, while the hybrid represents an and Corcos 1990). In fact, Mendel's paper teenth-century experimentalists in plant ever-decreasing proportion of the proge- can be seen as an attempt to provide a crossing are seen to fall into two distinct ny), while the final pages (pp. 44—48) are theoretical explanation for the phenome- groups: those who investigated the "es- devoted exclusively to transformation ex- na of reversion and transformation, both sence of the species as a whole" (Mayr periments. Mendel (1866; emphasis in of which were held to support the ortho- 1982) and those (such as Gallesio, Knight, original) writes: "Finally, the experiments dox doctrine of special creation. [L. A. Cal- Goss, Seton, and Sageret) who followed performed by Kolreuter, Gartner, and oth- lender (1988) has differentiated between the course of individual plant characters ers on transformation of one species into what he calls the orthodox doctrine of and who, therefore, like Mendel, worked of another by artificial fertilization deserve special creation (which asserted that all necessity with varieties. Nevertheless, special mention. Particular importance existing species were directly created by Mendel obviously felt that his conclusions was attached to these experiments; Gart- the hand of God and which denied the ex- had relevance to the former group, several ner counts them as among 'the most dif- istence of constant hybrids) and what he of whom he mentions in his paper (Kol- ficult in hybrid production.' " Mendel then calls the modified version proposed by reuter, Gartner, Herbert, Lecoq, Wichura), proposes the application of his "law valid Carolus Linnaeus in the middle of the eigh- while making no acknowledgment of the for Pisum": "If one may assume that the teenth century, which claimed that con- pioneers in his own field. Mayr (1982) ob- development of forms proceeded in these stant hybrids could arise.] serves: "Even though Mendel occasionally experiments in a manner similar to that in (1982) remarks: "It is highly significant calls himself a hybridizer and in his paper Pisum, then the entire process of transfor- that, as in the case of Darwin, it was the often refers to Kolreuter, Gartner, and oth- mation would have a rather simple expla- species question which inspired Mendel in er plant hybridizers, he himself does not nation." And in the penultimate paragraph his work on inheritance." at all belong to that tradition." of his paper, Mendel (1866) states: "The However, Mendel's experimental mate- Ever since Kolreuter's work with the to- success of transformation experiments led rial did not fulfill the criteria considered bacco plant in the 1760s, hybridizers had Gartner to disagree with those scientists necessary by theoretical of the sought to settle the question of immuta- who contest the stability of plant species time for hybridization pertaining to the or- bility and creation by experiment, and, as and assume continuous evolution of plant igin of species (Gasklng 1959): Mendel Callender (1988) has suggested, a proper forms. In the complete transformation of chose domestic varieties, not wild spe- understanding of such important theoret- one species into another he finds unequiv- cies, although he often uses the word ical categories as reversion and transfor- ocal proof that a species has fixed limits "species" in his paper, obviously tenden- mation, two phenomena that Kolreuter beyond which it cannot change. Although tiously, in reference to his garden peas. L. claimed to have discovered in the course this opinion cannot be adjudged uncon- C. Dunn (1965a) comments: "Kolreuter of his experimental investigations that re- ditionally valid, considerable confirmation and Gartner, to whom he [Mendel] refers, futed the existence of constant hybrids, is of the earlier expressed conjecture on the worked with true species hybrids differing essential to an interpretation of Mendel's variability of cultivated plants is to be in many variable intergrading characters paper. In this context, reversion was the found in the experiments performed by from which such a rule as Mendel envis- return of a hybrid by self-fertilization to Gartner." The last sentence obviously in- aged could not have been derived." And the two original types crossed, while dicates that Mendel thought that the "gen- Corcos and Monaghan (1993) write: transformation was the conversion of one erally applicable law" he had acquired "Hence, what Mendel was discussing as species into another already existing spe- supported Gartner's position. However, it the transformation of one species into an- cies by repeated of the hy- has been interpreted as meaning the exact other was really the transformation of one brid with one or the other of the two orig- opposite, as L. A. Callender has pointed variety into another." It has been argued inal parental forms. The purpose of such out: "Despite its clarity this paragraph has that the classification of peas was uncer- experiments was not to disprove the fixity been a source of endless confusion in the tain at the time and that Mendel states in of species, as so it may appear today, but literature. If this statement is to be taken his paper that their position in a classifi- to support the orthodox doctrine of spe- literally, as Mendel most assuredly intend- catory system was "completely immaterial cial creation, since no new species was ed it to be taken, then it says quite simply to the experiments in question," an atti- produced. that he gave conditional acceptance to the tude that has been labeled "cavalier" Joseph Gottlieb Kolreuter (1733-1806) view, expressed by Gartner, 'that species are (Haiti and Orel 1992). However, the im- and his successor Carl Gartner (1772- fixed within limits beyond which they can- portant point is that Mendel is not consis- 1850), to whom Mendel repeatedly refers, not change'. Nothing could be clearer. Nev- tent, referring to his experimental plants were firm believers in the orthodox doc- ertheless, interpretations of this passage as "varieties" in some contexts and as trine of special creation ["Constant hybrid have been given which are remarkable for "species" in other contexts, as Corcos and plant forms, they maintained, could not their extreme departure from accepted Monaghan (1993) have noted: "In this and did not exist" (Callender 1988)], and use in both the German and English lan- paragraph [detailing the selection of Darwin had cited them in The Origin of guages" (Callender 1988; emphasis in orig- plants for his experimental program] Men- Species as adversaries. [Darwin described inal). del uses the word 'variety' for his breeding Gartner as "so good an observer and so Thus, Mendel's concerns can be seen as lines, and yet in his 'Introductory Re- hostile a witness" (Darwin 1859).] consistent with the traditional science of marks' he wrote about hybrids between The first half of Mendel's (1866) paper his day (Max Wichura's book on true- species." Mendel also called his peas "va- (pp. 1-23) is devoted exclusively to the breeding willow hybrids had been pub- rieties" in his first letter to Nageli, in acquisition of his "generally applicable lished as recently as 1865) and also with

208 The Journal of Heredity 1996 87(3) the tumultuous times in which his paper combined. This also shows at the same contribution from both parents (Mayr appeared, when the Darwinian revolution time that the behavior of each pair of dif- 1982). (, in his book Men- was demanding a complete reassessment fering traits in a hybrid association is inde- del's Principles of Heredity, first published of man's concept of himself and his world pendent of all other differences in the two in 1909, wrote: "The seeds of course are in a way that no earlier revolution in the parental plants" (Mendel 1866; emphasis members of a generation later than that of physical had. David L. Hull in original). So no constant F, hybrids oc- the plant that bears them. Thus when a (1973), discussing the impact of Darwin's cur in any of Mendel's experiments. Al- cross is made the resultant seeds are F,, book, writes: "Seldom in the history of though true-breeding forms appear among showing the dominant character yellow- ideas has a scientific theory conflicted so the progeny of the hybrids (Fj) in the di- ness or roundness, but the seed-skins are openly with a metaphysical principle as hybrid and trihybrid experiments, they maternal tissue.") Consequently, the ap- did evolutionary theory with the doctrine are only the result of a recombination of pearance of the seed coat relevant to Men- of the immutability of species." And Au- existing alternatives. Nothing new comes del's formulae is not observable in com- gustine Brannigan (1979), in an article en- into being at either the phenotypic or ge- bination with the two embryonic traits in titled "The Reification of Mendel," com- notypic level, for Mendel's abstract sym- the same plant or in the same year. Men- ments: "If anything, Mendel's reputation bolic notation implies that Darwin's "ele- del does not mention this, nor does he was modest not because he was so radi- mental atoms" are discrete entities that re- state the very complex procedures nec- cally out of line with his times but because main immutable throughout both time and essary to overcome the serious difficul- his identity with his contemporaries was space, irrespective of how many genera- ties, reporting only that this "experiment so complete!" One of Mendel's contempo- tions or character pairs are involved. [In- was conducted in a manner quite similar raries was Gustave Niessl [in fact, Hugo terestingly, Mendel refers to the internal to that used in the preceding one" (Men- Iltis records that Mendel "owed a good determinants he postulated in order to ac- del 1866), all of which cast doubt on deal to Niessl's insight and clarity" (Iltis count for his "doctrine of hybridization" whether he actually performed the exper- 1932)], who was secretary of the natural (Sinoto 1971) as "elements": "... those el- iment, thus substantiating Di Trocchio's history society to which Mendel had pre- ements of both cells that cause their dif- (1991) claims. sented his paper in 1865, and he was still ferences" (Mendel 1866). Meijer (1983) Mendel says nothing at all about a tet- an active official at the turn of the century writes: "Whenever Mendel discusses the rahybrid experiment, although his popu- when Mendel's paper was revived. Bran- material composition of the germ-cells, he lational generalizations immediately fol- nigan (1979; emphasis in original) ob- uses the word 'elements' ('Elemente')."] lowing the trihybrid experiment are pro- serves: "In 1902, he [Niessl] suggested This is in marked contrast to Darwin, who jections from four pairs of character dif- that it was believed in the that Men- argued that there is a continual produc- ferences: "For instance, when the parental del's work was in competition with, as op- tion of small heritable variations upon types differ in four traits the series con- posed to complementary to, that of Darwin which his mechanism of natural selection 4 tains 3" = 81 terms, 4 = 256 individuals, and Wallace." [The problem of hybridiza- could act. Callender (1988), in his article 4 and 2 = 16 constant forms; stated differ- tion and its relationship to evolution had entitled ": An Opponent of ently, among each 256 offspring of hybrids been a frequent theme since the founding Descent with Modification," observes: "... there are 81 different combinations, 16 of of the society by Mendel and his friends Mendel, of course, denied the very basis which are constant" (Mendel 1866). Men- and acquaintances in December 1861 of the evolutionary process, modification del then extrapolates to any number of (Brannigan 1979).] of hereditary characteristics." And Callen- traits, even those he had excluded at the der elaborates: "... it is a striking fact that outset because they did not fulfill his cri- Mendel also compares his Pisum "law" the multitude of commentators who have teria for selection: "The complete agree- with the reversion experiments reported so consistently held that Mendel was in ment shown by all characteristics tested by Kolreuter and Gartner. After stating essential agreement with the theory of probably permits and justifies the assump- that the monohybrid seeds and plants evolution have singularly failed to dem- tion that the same behavior can be attrib- have been followed through four to six onstrate in his theory of heredity any uted also to the traits which show less dis- generations (and just before presenting mechanism by which descent with modi- tinctly in the plants, and could therefore his formula extrapolating to any number fication might have come about. Indeed, not be included in the individual experi- of generations), Mendel (1866) writes: only the merest handful have ever drawn ments. An experiment on flower stems of "The observation made by Gartner, Kol- attention to the fact that a concept of he- different lengths gave on the whole a rath- reuter, and others, that hybrids have a ten- reditary is entirely absent from er satisfactory result, although distinction dency to revert to the parental forms, is the whole of Mendel's published work." also confirmed by the experiments dis- and classification of the forms could not cussed." be accomplished with the certainty that is Of particular significance is the single indispensable for correct experiments" Therefore, no constant hybrids arise in trihybrid experiment, from which Mendel (Mendel 1866). This suggests that Mendel the monohybrid experiments, and Mendel obtains the expected result despite the re- acquired his seven traits by prior experi- concludes that the same "law of develop- calcitrant data. In this experiment, Mendel ment, which again correlates with the ment" applies in the dihybrid and trihy- includes the color of the seed coat with methodology Di Trocchio argues Mendel brid experiments: "Therefore there can be the familiar traits of seed shape and cot- must have used to obtain his data. Mayr no doubt that for all traits included in the yledon color that he had used for the di- (1982) comments: "The 22 varieties experiments this statement is valid: The hybrid experiment, although the seed coat [which Mendel (1866) reports he "planted progeny of hybrids in which several essen- is maternal tissue and therefore its ap- annually throughout the entire experimen- tially different traits are united represent the pearance following each artificial fertiliza- tal period"] differed from each other by terms of a combination series in which the tion is determined solely by the maternal far more than the seven selected traits, series for each pair of differing traits are genetic constitution and not by an equal

Bishop • Mendel's Opposition to Evolution and to Danvin 209 but Mendel found the other traits unsuit- character or the other, not both." The serves: "The final blow, or so it seemed— able because either they produced contin- same point had been made by Mendel in to pangenesis, inheritance of acquired uous or quantitative variation not suitable his second letter to Nageli: "The course of characters, inequality of parental contri- for the study of the clear-cut segregation development consists simply in this; that bution and —oc- he was interested in, or else they did not in each generation the two parental traits curred in 1900 when Mendelian and de segregate independently." It also supports appear, separated and unchanged, and Vriesian theories of inheritance reached Fisher's (1936) evaluation of Mendel's pa- there is nothing to indicate that one of the scientific world." Mendel's onslaught, per, of which L. C. Dunn (1965b) wrote: them has either inherited or taken over however, unlike that of de Vries, was "The impression that one gets from Men- anything from the other" (Stern and Sher- mounted in the early 1860s, when the del's paper itself and from Fisher's study wood 1966). Eiseley (1958) comments of world was agog with Darwin's ideas and of it is that Mendel had the theory in mind this passage: "Heredity and variation in when biological knowledge and theory when he made the experiments reported the old Darwinian sense could, therefore, were entirely different. in the paper. He may even have deduced not be synonymous. The unit factors had Darwin's belief in the inheritance of ac- the rules from a particulate view of hered- a constancy which the Darwinians had quired characters was increasingly played ity which he had reached before beginning failed to guess." down in the twentieth century—after the work with peas. If so, the outcome of his acceptance of 's theory experiments constitutes, in Fisher's of the isolation of the from so- Darwin and Heredity words, not discovery but demonstration." matic influence—so much so, in fact, that In his conclusion, Mendel (1866) dis- Darwin, of course, believed throughout his the inheritance of acquired characters be- cusses the combination series he has ac- life in blending inheritance, like all his con- came the central theme of acrimonious de- quired, in which "the members of the se- temporaries ["In Darwin's time everybody bate between French and English biolo- ries tend equally toward both original par- except Mendel ... thought that inheri- gists and philosophers, who lined up on ents in their internal makeup" [converse- tance was blending" (Dawkins 1986)], and opposing sides behind their heroes. Al- ly, Darwin (1859) had argued that when in the inheritance of acquired characters though, as Maynard Smith (1982) has "hybrids are able to breed inter se, they for both corporeal structures and behav- pointed out, it was not Lamarck's theory transmit to their offspring from generation ior. In fact, Darwin put forward his own of heredity that Darwin rejected but his to generation the same compounded or- theory of heredity, "Pangenesis," in 1868 idea that evolution could be explained by ganization"], and he declares: "One sees in order to account not only for the pro- an inner drive toward complexity. how risky it can sometimes be to draw duction of variation but also for the inher- It was the hereditary aspect of evolu- conclusions about the internal kinship of itance of acquired characters. It is gener- tionary theory that most fascinated Dar- hybrids from their external similarity." ally thought that this was a retreat on Dar- win. In a letter to T. H. Huxley, some years As Arnold Ravin (1965) has pointed out, win's part in the face of mounting criticism before the publication of The Origin of Spe- Mendel's theory was based upon the as- of his mechanism of natural selection, but cies, Darwin had remarked: "Approaching sumption of equality throughout all stages historians have shown that Darwin's ideas the subject from the side which attracts of the life cycle: equal that unite on heredity were developed over the me most, viz inheritance, I have lately at random to form equal zygotes that grow years in concert with his theory of de- been inclined to speculate" (Burkhardt into equal plants, reproducing equally scent with modification ["... the hypoth- and Smith 1990). Darwin drew a sharp line generation after generation. This, of esis represents the crystallisation of Dar- of demarcation between the inheritance of course, is the antithesis of Darwin's theo- win's thoughts over a period of a quarter what later came to be known as Mendelian of a century, thoughts that began with his ry of differential survival and differential characters and those acquired by natural wonder at the ability of a planarian to re- reproductive success. Also, Mendel fo- selection. In the first edition of The Origin generate after division" (Olby 1985)], and cused on discontinuous variation: "Men- of Species, he states: "Looking to the cases it is clear from the first edition of The Or- del's concept of discrete characters was which I have collected of cross-bred ani- igin of Species that Darwin took the inher- mals closely resembling one parent, the completely opposed to Darwin's idea of itance of acquired characters for granted. continuous variation" (Orel and Kuptsov resemblances seem chiefly confined to Darwin devotes a whole chapter to in- characters almost monstrous in their na- 1983). Mayr (1982) remarks: "Even though stinct, and in his discussion of the hive- Darwin acknowledged the existence of dis- ture, and which have suddenly ap- bee (Mendel, incidentally, also worked peared—such as albinism, melanism, de- continuous variation as a separate cate- with bees), he states: "The motive power ficiency of tail or horns, or additional fin- gory, he considered it evolutionarily un- of the process of natural selection having gers and toes; and do not relate to char- important." been economy of wax; that individual acters which have been slowly acquired When Mendel's paper was revived at the swarm which wasted least honey in the se- by selection" (Darwin 1859). This passage beginning of the twentieth century, the pu- cretion of wax, having succeeded best, appears unaltered in the sixth (and final) rity of the gametes was highlighted by Wil- and having transmitted by inheritance its edition, published in 1872. liam Bateson (1901; emphasis in original) newly acquired economical instinct to in his introduction to the first English new swarms, which in their turn will have Darwin began The Variation of Animals translation: "The conclusion which stands had the best chance of succeeding in the and Plants under Domestication (in which out as the chief result of Mendel's admi- struggle for existence" (Darwin 1859). he presented his theory of heredity) in rable experiments is of course the proof 1860, a year after the publication of the that in respect of certain pairs of differ- Mendel's theory was obviously con- first edition of The Origin of Species, and it entiating characters the germ cells of a hy- structed to deny all Darwin's ideas about was first published in 1868, two years after brid, or cross-bred, are pure, being carri- heredity and thus his theory of descent the appearance of Mendel's Pisum paper ers and transmitters of either the one with modification. George (1982) ob- and a year before Mendel's presentation of

210 The Journal oJ Heredity 1996 87(3) his Hieracium paper. [Interestingly, Mendel known that Mendel did in his paper: "Tran- character that Mendel chose for his first made numerous marginalia in Darwin's sitional forms were not observed in any ex- monohybrid experiment (and also for chapter on inheritance (Orel 1971) (the periment" (Mendel 1866; emphasis in orig- both the dihybrid and trihybrid experi- German edition of The Variation was pub- inal). [, one of Mendel's "re- ments) is caused by an insertion sequence lished in the same year as the English edi- discoverers," later commented: "The lack that prevents normal expression of a tion), and, as we have seen, he mentioned of transitional forms between any two sim- for an enzyme (the presence of which Darwin in his Hieracium paper.] In this ple antagonistic characters in the hybrid gives rise to the alternative character, massive, two-volume work, the first part of is perhaps the best proof that such char- roundness), and this has important impli- the long-promised addition to The Origin acters are well delimited units" (de Vries cations to Mendelian theory. (the second part on the variability of or- 1900).] Thus, the difference between Dar- Madan Bhattacharyya and his col- ganic beings in a state of nature was never win's and Mendel's ideas about inheri- leagues point out that the de- written), Darwin devoted only five pages tance was not only a question of interpre- scription of wrinkled pea seeds that Men- to Mendelian-type inheritance. The sec- tation: Mendel's "facts" were different del provided fits only two loci described tion, entitled "On certain characters not from Darwin's—and from those of all his among commercial cultivars, r and rb, and blending," concludes: "All the characters contemporaries. [For instance, Meijer that the latter would have been unavail- above enumerated, which are transmitted (1983; emphasis in original) notes: "Men- able to Mendel, and they comment: "It has in a perfect state to some of the offspring del's views appear to have been very dif- been widely accepted that the wrinkled- and not to others—such as distinct col- ferent from Nageli's, and also his facts seed character described and studied by ours, nakedness of skin, smoothness of were different."] Mendel (1865) was an of the r locus" leaves, absence of horns or tail, additional Darwin (1875) began the conclusion to (Bhattacharyya et al. 1990). The insertion toes, pelorism, dwarfed structure, etc.— his theory of heredity: "The hypothesis of is thought to be located in an of the have all been known to appear suddenly Pangenesis, as applied to the several great SBE1 gene, which codes for an enzyme in individual animals and plants. From this classes of facts just discussed, no doubt called the starch-branching enzyme 1, and fact, and from the several slight, aggregat- is extremely complex, but so are the it is estimated that it would cause loss of ed differences which distinguish domestic facts." the last 61 amino acids of the SBE1 pro- races and species from one another, not At the time when Darwin and Mendel tein, resulting in defects in starch, lipid, being liable to this peculiar form of trans- wrote, it was impossible for a scientist to and biosynthesis in the seed mission, we may conclude that it is in be anything but speculative about the na- (Bhattacharyya et al. 1990). Therefore, some way connected with the sudden ap- ture of inheritance, for it was not until wrinkled pea seeds are abnormal pea pearance of the characters in question" 1869 that Friedrich Miescher elucidated seeds, the equivalent of Darwin's "sports" (Darwin 1875). the chemical composition of the cell nu- and Garrod's "inborn errors of metabo- In the section of The Variation entitled cleus, and it was even later that it was un- lism," and round pea seeds are normal pea seeds. There are no instructions "for" "Prepotency in the transmission of char- derstood that the nucleus of the zygote is wrinkledness—only defective instructions acter," Darwin presented in careful detail formed by the fusion of the egg nucleus for roundness. In other words, there are experiments very similar to Mendel's. [As and a male nucleus derived from a sper- not two different units of information, one Mayr (1983) has pointed out, Darwin was matozoon. coding for wrinkledness and the other for A. R. Wallace, the codiscoverer with Dar- not only a meticulous observer but "also roundness; there is only one unit, the wild- win of the principle of natural selection, a gifted and indefatigable experimenter type gene coding for roundness, with or lived to see the great cytological advances whenever he dealt with a problem, the so- without an insertion sequence. lution of which could be advanced by an at the end of the nineteenth century—and experiment."] He writes: "Now I crossed the rise of Mendelism. George (1971) Furthermore, the insertion sequence is the peloric snapdragon ( ma- states: "... in 1910, in the 'World of Life' 0.8 kb long, and, whereas the normal SBE1 jus), described in the last chapter, with Wallace made his last comments on Men- gene transcript in round seeds is 3.3 kb, pollen of the common form; and the latter, delism. He still objected to the idea be- the aberrant transcript in wrinkled seeds reciprocally, with peloric pollen. I thus cause the Mendelian characters were ab- is 4.1 kb, suggesting that the nuclear DNA raised two great beds of seedlings, and not normalities and, therefore, detrimental to of the homozygous recessive wrinkled pea one was peloric ... The crossed plants, the species under natural conditions. He seeds contains the entire information for which perfectly resembled the common stressed, once more, their rarity: "The phe- the enzyme (i.e., for roundness), although snapdragon, were allowed to sow them- nomena on which these theories are found- it cannot be expressed. [J. R. S. Fincham selves, and out of a hundred and twenty- ed seem to me to be mere insignificant by- (1990) writes: "The size difference was seven seedlings, eighty-eight proved to be products of heredity, and to be essentially shown to segregate from crosses with the common snapdragons, two were in an in- rather self-destructive than preservative. r locus, as if the r mutation were due to an termediate condition between the peloric They form one of nature's methods of get- insertion of an extraneous sequence into and normal state, and thirty-seven were ting rid of abnormal and injurious varia- the wild-type R gene."] Thus, the infor- perfectly peloric, having reverted to the tions. The persistency of Mendelian char- mation for roundness is not being elimi- structure of their one grandparent" (Dar- acters is the very opposite of what is need- nated at meiosis (although, of course, dis- ed amid the ever-changing conditions of win 1875). junction of with their differ- nature.'" The occurrence of intermediate types is ent complements occurs), and conse- very significant, for it categorically rules quently all gametes for both out the possibility of establishing a defi- Mendel's Wrinkled Pea Seeds (and for the heterozygote) must carry the information for roundness, a fact that calls nite ratio between only the two types re- Interestingly, molecular studies have re- into question the validity of the first Men- sembling the parental forms, as it is well cently revealed that the wrinkled-seed

Bishop • Mendel's Opposition to Evolution and to Darwin 211 delian law, the law of segregation. As Do- explained by somatic excision of the ele- that he was familiar with The Origin of ver (1986) has observed in a different con- ments. For instance, in the experiment Species, Darwin's themes of evolution, text: "The traditional algebraic represen- with yellow/green seeds (which Mendel population, and heredity being echoed tation of the Mendelian segregation of used for his second monohybrid experi- by Mendel, and that he was opposed to from one generation to the next is, ment and, like the round/wrinkled char- Darwin's theory: Darwin was arguing strictly speaking, a description of the seg- acter pair, for both the dihybrid experi- for descent with modification through regation of chromosomes." [The second ment and trihybrid experiment), Mendel natural selection, Mendel was in favor Mendelian law, the law of independent as- observed a "partial disappearance of the of the orthodox doctrine of special cre- sortment, was disproved many years ago, green coloration" (Mendel 1866) in some ation. as Mayr (1982) has noted, despite its per- seeds. 4. Darwin's theory was based on differ- sistence as textbook orthodoxy: "Finally, Now, in retrospect, it can be seen exact- ential survival and differential repro- free assortment is also [in addition to the ly what Mendel did: he deliberately chose ductive success, Mendel's on equality short-lived "law of dominance"] not a val- characters exhibiting a most unusual pat- throughout all stages of the life cycle: id 'law,' because it was discovered soon tern of inheritance ("this peculiar form of equal gametes that unite at random to after 1900 that characters could be transmission," as Darwin referred to Men- form equal zygotes that grow into equal 'linked,' by having their determinants on delian-type inheritance) because he want- plants, reproducing equally generation the same ."] ed to demonstrate stasis, formulated a after generation. Although there is no evidence of exci- highly improbable theory, and then ex- 5. Darwin's concepts were continuous sion of the insertion sequence that pro- trapolated to all other modes of inheri- variation, mutation, and "soft" heredi- duces wrinkled pea seeds, there are in- tance. But it is today known that the ge- ty; Mendel espoused discontinuous creasing reports of somatic and germ-line nome is extraordinarily fluid, as a conse- variation and "hard" heredity without excision of such elements in fruit flies and quence of a variety of mechanisms of non- mutation. other organisms, leading to reversion to reciprocal DNA transfer within and 6. The theoretical significance of Mendel's wild type. Thus, organisms scored as mu- between chromosomes, and it is obvious, first monohybrid experiment (with tants in one generation can give rise to as the early opponents of Mendelism seed shape) and of both the dihybrid normal progeny in subsequent genera- maintained (Wallace was by no means and trihybrid experiments (in which tions. This, of course, has important im- alone in his objections), that the type of the same trait was included) is ques- plications to all aspects of Mendelian the- transmission upon which Mendel focused tionable in light of molecular studies ory: gametic transmission of information, (that represented largely by dis- showing that the wrinkled-seed pheno- fixed ratios, predictions of long-term sta- eases and laboratory mutants) is the ex- type is caused by an insertion se- bility, the definition of "rate of mutation," ception and not the rule: "The ubiquity of quence that prevents normal expres- and even Mendelian terminology. (Most of genomic turnover mechanisms both with- sion of the gene for an enzyme, the these mutant organisms, like Mendel's in and between genes (single-copy and presence of which gives rise to the an- wrinkled pea seeds, are labeled "homozy- multigene families) means that few genes tagonistic character, roundness (Bhat- gous recessive" in the Mendelian system, will be found that are refractory to the tacharyya et al. 1990). according to which information for com- mechanisms involved. It is conceivable plex normal characters has been lost and that strict Mendelian genes and stable cannot be reacquired.) Mendelian populations in Hardy-Weinberg References These findings would correlate with Dar- equilibria do not exist except as observed Bateson W, 1901. 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(1990) points out that transposable DNA that had been raging since the publi- Brannlgan A, 1979. The relficatlon of Mendel. Soc Stud elements have been characterized from cation of Darwin's The Origin of Species Scl 9:423-154. several plant species, including antirrhi- in 1859. Burkhardt F and Smith S (eds), 1990. The correspon- dence of , vol. 6:1856-1857. Cambridge: num, and it is known that excision events 2. Mendel could have come into contact Cambridge University Press. are strongly dependent upon the environ- with Darwin's ideas as early as 1860, Callender LA, 1988. Gregor Mendel: an opponent of de- ment, occurring, for instance, less fre- when the first German edition of The scent with modification. Hist Scl 26:41-75. quently in plants grown inside a green- Origin of Species was published and a Corcos AF and Monaghan FV, 1990. Mendel's work and house than in those grown outside, where chapter was printed in a journal that its rediscovery: a new perspective. Crit Rev Plant Scl the temperature is lower.] was available to him. This would have 9{3):197-212. It is possible that other recessive char- given Mendel a time frame for his ex- Corcos AF and Monaghan FV, 1993. Gregor Mendel's ex- periments on plant hybrids: a guided study. New acters Mendel chose could also be caused perimental program that correlates Brunswick, New Jersey: Rutgers University Press. by insertion sequences in wild-type genes with the methodology Di Trocchio Darwin CR, 1859. by means of and that the departure from the expected (1991) claims he must have used to ob- natural selection, 1st ed. : Murray, reprinted phenotypes that Mendel recorded but ig- tain his data. 1950, London: Watts. nored in formulating his theory could be 3. The content of Mendel's paper shows Darwin CR, 1875. The variation of animals and plants

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Bishop • Mendel's Opposition to Evolution and to Darwin 213