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MENDEL IN GENETICS TEACHING: SOME CONTRIBUTIONS FROM HISTORY

OF SCIENCE AND ARTICLES FOR TEACHERS*

Charbel N. El-Hania

a. History, Philosophy, and Biology Teaching Lab (LEFHBio), Institute of Biology, Federal University of Bahia, Brazil.

Address for correspondence: Rua Barão de Jeremoabo, s/n – Ondina, Salvador-BA, Brazil. ZIP: 40170-115. Phone: 55 71 3283 6568. E-mail: charbel@ufba.br

Abstract. School science descriptions about Mendel and his story are problematic because several statements that are controversial among historians of science are repeated over and over again as if they were established facts. Another problem is the neglect of other scientists working on inheritance in the second half of the 19th century, including Darwin, Spencer, Galton, Nägeli, Brooks, Weismann and de Vries, who paved the way for the reinterpretation of Mendel’s work in 1900. These problems are often found in textbooks and are likely to be present in school science throughout the world. Here, we discuss the contributions that history of science and papers published in journals that target teachers may bring to improve how school science deals with Mendel and his contributions. Evidently the idea is not that school teachers could solve problems still under discussion in the historical literature. The point is, rather, that it is important to avoid treating Mendel’s contributions as uncontroversial, mentioning, for instance, that there are ongoing debates on whether he proposed the laws named after him, appealing to invisible factors underlying phenotypic traits that are seen as the heritable potentials for those traits, and would in due time be known as genes. History of science can contribute to put the mythic Mendel into question in the science classroom, bringing school science closer to the controversies around the interpretation of his work. Keywords: Mendel; Heredity; Darwin; Genetics; History of science.

1. Introduction

In textbooks and, generally speaking, Genetics teaching, Mendel is often portrayed as the

first scientist to propose a theory of heredity. Moreover, other scientists who studied

inheritance in the 19th century and paved the way to the emergence of Genetics as a

scientific discipline are typically ignored (Kampourakis 2013). Mendel is generally taken

to be a sort of lone thinker, neglected by his contemporaries to be rediscovered only 35

years later, when he was recognized as the founding father of Genetics.

These school science descriptions are problematic for several reasons. First, the

historical description of Mendel’s works is inaccurate in some respects, and in some other

respects at least not consensual, if we consider debates among historians of science.

                                                            * This is a previous version of the paper, in relation to the one published in Science & Education, available at http://link.springer.com/article/10.1007%2Fs11191‐014‐9685‐y, DOI: 10.1007/s11191‐014‐9685‐y. There were some minor changes in the published version, which should be referred to, if cited. 

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Second, the study of heredity in the 19th century is limited to a supposedly isolated and

heroic friar, even though Mendel was not truly isolated and was not primarily interested

in inheritance, but in hybridization. Third, as noted, these descriptions neglect the work

of other researchers who addressed inheritance as a major topic in their studies.

The publication of the Origin of Species raised a lot of interest on this topic, and

several contemporary scholars, including Darwin himself, tried to build a theory of

heredity to complement the theory of natural selection (Gayon 1998). Not only Darwin,

but also Herbert Spencer, Francis Galton, William Keith Brooks, Carl von Nägeli, August

Weismann, and Hugo de Vries developed theories of heredity at that period. Mendel was,

in fact, an outsider to this community (Kampourakis 2013). Nägeli was aware of his work

and, perhaps, other contemporary naturalists, such as Darwin – as we will discuss below

–, but it is true, anyway, that Mendel had no true impact before his rediscovery. In 1900,

the landscape of scientific ideas had changed and Mendel’s work was not only

rediscovered, but also co-opted and reinterpreted by its rediscoverers and, broadly

speaking, by Mendelian geneticists. After Mendel’s work was reinterpreted under the lens

of subsequent developments, it became difficult for most people not to read back in

Mendel’s papers aspects and ideas that are not so evidently there, or even that are

evidently not there.

In this paper, we discuss contributions that the literature on history of science and

articles published in journals for teachers can bring to the treatment of Mendel’s story in

Genetics classrooms. We intend to show how important it is to bring school science closer

to the controversies around the interpretation of his work.

2. Mendel’s work and its interpretation in the historical literature

Mendel performed his famous experiments in the Augustinian Monastery of St.

Thomas at Brünn, at that time part of the Austro-Hungarian Empire (currently Brno, in

the Czech Republic). Iltis (1932/1966) describes the monastery as one of the chief centers

of the spiritual and intellectual life of the Empire. Since 1840 efforts to give a scientific

perspective to breeding practices had been taking place in Brünn (Wood and Orel 2005).

Mendel, who had studied in Vienna with important contemporary scientists, such as

Christian Doppler and Franz Unger, indeed brought a new perspective to the studies on

breeding. But why did he fail to have any impact at his own time?

MacRoberts (1985) distinguishes two broad kinds of hypotheses proposed to

explain why Mendel’s work did not have such impact: on the one hand, cognitive

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hypotheses, which assume that Mendel’s work was known, but either ignored,

misinterpreted, or rejected by his contemporaries; on the other, non-cognitive hypotheses,

claiming that Mendel’s work was not known.

However, Mendel’s work was indeed known by important contemporaries, such

as Nägeli and, possibly, Darwin (see below). Although he published his work in a minor

scientific journal, the issue containing it was sent to 134 scientific institutions (Kruta and

Orel 1976), including the Royal Society and the Linnean Society (Brannigan 1979). This

is certainly no guarantee that many associates of those societies really read the paper, as

suggested by the fact that it was rarely quoted before 1900 (Olby and Gautrey 1968). For

MacRoberts, Mendel’s work had a limited impact because he was not known at the level

of informal communication, with the exception of his exchanges with Nägeli from 1866

to 1873 (Mendel 1950). In the end, a combination of the two kinds of hypotheses

mentioned by MacRoberts may explain the limited impact of Mendel’s work: not only

few contemporaries were aware of his work, but, also, those who knew it could not

reconcile his approach – largely mathematical and statistical – with their own theories.

Concerning the question of whether Mendel was really studying inheritance, it is

no coincidence that the German words for heredity and their derivatives are not found in

his 1866 paper (Olby 1979; Brannigan 1979; Monaghan and Corcos 1990). He was

mostly interested in the question of whether hybridization could produce new species,

working under the research tradition of earlier hybridists such as Kölreuter and von

Gärtner, who had concluded that new species could not be formed by hybridization, and

his own teacher, Unger, who had reached the opposite conclusion (Olby 1985; Endersby

2007; Kampourakis 2013). Mendel’s conclusion was that hybrids do not form stable

species, since they tend to return to the parental forms:

The observation made by Gärtner, Kölreuter, and others, that hybrids are inclined to revert

to the parental forms, is also confirmed by the experiments described (Mendel 1866/1996,

p. 14).

Was he also looking for laws of inheritance? It is true that he says that “so far, no

generally applicable law governing the formation and development of hybrids has been

successfully formulated” (Mendel 1866/1996, p. 1). However, it is still a matter of great

controversy among scholars whether he was really aiming at a more general theory of

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heredity, or was focused on a theory of hybrid development and the role of hybridization

in the origin of species. On the one hand, statements like the one above may incline us to

read his work as an attempt to build a theory of heredity. On the other, the second goal is

more straightforwardly related to the research tradition in which he was working, and,

also, is more clearly stated in his paper.

There is also a lot of controversy among scholars regarding whether Mendel’s

papers does contain the major concepts and laws of Genetics, as it is usually thought by

both biologists and lay people. It is not clear, for instance, if the laws of segregation and

independent assortment are indeed stated by him. Certainly, his impact cannot be

disputed, since his 1866 paper was taken by classical geneticists as the founding paper of

their discipline, and, thus, clearly exerted a huge influence on science after 1900.

However, we can put into question if those geneticists were right in taking Mendel’s paper

as the founding work of their discipline, or if they were reading back in Mendel’s writings

subsequent developments made by themselves. If the answer tends to the second horn,

then we have been reading too much in Mendel’s articles since then. Evidently, this

conclusion has much impact on school science and demands that we portray the story of

Mendel differently from what has been up to now the dominant approach.

To ascertain if Mendel indeed formulated the laws attributed to him, it is

consequential to examine whether he was just talking about characters or also about

underlying hereditary elements. To our understanding, Mendel does not frame the

explanation of the experimental results in his 1866 paper by appealing to hereditary

elements, such as the “factors” often supposed to be a central concept in his arguments.

Based on the works of Heimans (1968, 1971), Olby (1979) advanced precisely this view,

calling attention to the fact that Mendel wrote about characters (merkmale), that is, he

was constantly referring, in current terminology, to phenotypes, not genotypes. Mendel

writes, for instance:

Einige ganz selbständige Formen aus diesem Geschlechte besitzen constante, leicht und

sicher zu unterscheidende Merkmale, und geben bei gegenseitiger Kreuzung in ihren

Hybriden vollkommen fruchtbare Nachkommen (Mendel 1866, p. 6, emphasis added).

In the English translation, originally made by William Bateson in 1901, we read:

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Some thoroughly distinct forms of this genus possess characters which are constant, and

easily and certainly recognizable, and when their hybrids are mutually crossed they yield

perfectly fertile progeny (Mendel 1866/1996, p. 3, emphasis added).

This usage of the term “merkmale” continues throughout the 1866 paper,

suggesting that he was focusing his discussion on characters such as seed color or form.

Falk (1986) argues, however, that “merkmale” literally means “markers” and, thus, it

could be the case that Mendel realized that the characters were actually only the external

markers of unobservable yet real hereditary units. He follows in this interpretation

Sandler (1983), who argued that Mendel narrowed his attention to the elements of the

cells that carried the potentials for the traits. This is exactly the interpretation disputed by

Olby and several other scholars. Here is the sentence that Falk quotes in order to make

his case:

In our experience we find everywhere confirmation that constant progeny can be formed

only when germinal cells and fertilizing pollen are alike, both endowed with the potential

for creating identical individuals (Mendel 1866, p. 24, as quoted in Falk, 1986, pp. 135-

136, emphasis added).

This same passage appears in Bateson’s translation as follows:

So far as experience goes, we find it in every case confirmed that constant progeny can

only be formed when the egg cells and the fertilizing pollen are of like character, so that

both are provided with the material for creating quite similar individuals (Mendel

1866/1996, p. 20, emphasis added).

The key term in the original is “Anlage”, translated as “potential” in the version

used by Falk and as “material”, in Bateson’s version. The argument goes on as follows:

We must therefore regard it as certain that exactly similar factors [in German, Factoren]

must be at work also in the production of the constant forms in the hybrid plants (Mendel

1866/1996, p. 20, emphasis added).

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Finally, another term used by Mendel that might hint at hereditary units is

“element” (elemente), as shown by the following passage:

… This development follows a constant law, which is founded on the material composition

and arrangement of the elements [in German, Elemente] which meet in the cell in a

vivifying union (Mendel 1866/1996, p. 35, emphasis added).

First, we should notice that the passages referring to “Factoren”, “Anlage”, and

“Elemente” are virtually exceptions in an argument constructed throughout the paper at

the level of characters (merkmale). This makes it difficult to accept Falk’s interpretation

that Mendel might be talking about markers for hereditary units that would carry or be

the potentials for a trait, or, else, arguments from other authors who maintain that

Mendel’s interpretation was based on material hereditary elements (e.g., Hart and Orel

1992; Fairbanks and Rytting 2001). The words “Factoren” and “Anlage” appear each only

one time in the original paper. The term “Elemente” is more frequent, appearing 10 times.

However, “merkmale” appears 140 times, and each time we can understand it as meaning

“character”. This suggests that it might be too much to interpret Mendel’s arguments as

pointing out to hereditary units that would be the potentials for traits from such limited

occurrences of words that can themselves have a variety of meanings.

However, more important for the sake of our conclusion is the fact that, by

claiming that Mendel was referring to hereditary elements that are the potential for traits,

we would be ascribing to him an understanding of the distinction between genotype and

phenotype. But this distinction only appeared in 1908 when Wilhelm Johannsen

distinguished between two ideas embedded in the term ‘unit-character’, then largely used:

the idea of (1) a visible character of an organism which behaves as an indivisible unit of

Mendelian inheritance, and, by implication, (2) the idea of that thing in the germ-cell that

produces the visible character. Interestingly enough, Falk (1986) himself argues that

Johannsen was the first to be entirely successful in explicating the difference between the

potential for a trait and the very trait, opening the door to a clear discrimination between

genotype and phenotype, and, furthermore, between units in the genotype (‘genes’) and

in the phenotype (‘phenes’ – a term which was largely forgotten). It is not likely, then,

that Mendel would have hinted at this distinction more than four decades before.

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In sum, it seems reasonable to conclude that we are reading the distinction

between genotype and phenotype back into Mendel’s 1866 paper when we see in his

sporadic use of the terms Factoren”, “Anlage”, and “Elemente” a reference to the idea of

hereditary units. Subsequently, Falk acknowledged, in a paper with Sarkar (Falk and

Sarkar 1991), that the case for Mendel’s appeal to particulate hereditary elements is not

strong. Moreover, if Mendel was thinking in terms of hereditary elements or particles,

why wasn’t he explicit about this, arguing about how these elements are transmitted to

the offspring and are related to the appearance of manifest characters? That these

arguments could be put forward is shown by the fact that all scientists who were studying

heredity in the second half of the 19th century were explicit about these issues

(Kampourakis 2013). Moreover, Mendel had the appropriate background from physics to

postulate the existence of particles that could explain his results (Monaghan and Corcos

1990). However, he did not provide this argument in any explicit manner.

One could argue that Mendel’s use of the words “dominant” and “recessive”

(always as adjectives, not substantives) suggests that he was thinking about hereditary

elements underlying the traits. Nevertheless, Mendel uses these terms to refer to the

characters themselves:

Henceforth in this paper those characters which are transmitted entire, or almost unchanged

in the hybridization, and therefore in themselves constitute the characters of the hybrid, are

termed the dominant, and those which become latent in the process recessive (Mendel

1866/1996, p. 7).

This interpretation is consistent with a fact noticed by Mayr (1982), namely, that

Mendel used the same symbol for what we now consider the recessives of two

independent loci, suggesting that he was not entertaining the concept of genetic loci with

alleles.

Coming back to the issue of so-called Mendel’s laws, there is a great deal of

polemics in the literature. Kampourakis (2013) acknowledges the existence of passages

in Mendel’s 1866 paper that are suggestive of the laws of segregation and independent

assortment. Olby (1979) and Callender (1988) argue that the law of segregation is not

present in his 1866 paper, while Hartl and Orel (1992) argue to the contrary. Falk and

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Sarkar (1991) consider that Mendel came close to the formulation of the law of

segregation when he states that

in the ovaries of the hybrids there are formed as many sorts of egg cells, and in the anthers

as many sorts of pollen cells, as there are possible constant combination forms, and that

these egg and pollen cells agree in their internal compositions with those of the separate

forms (Mendel 1866/1996, p. 20).

It is clear, anyway, that if Mendel did not entertain the concept of hereditary

elements or factors, his formulation of this law could not be the same later used in

classical Genetics.

It has also been argued that Mendel did not state the law of independent assortment

(Monaghan and Corcos 1990). Falk and Sarkar (1991) and Orel and Hartl (1994) consider,

however, that this law is found in sentences such as the following one:

…the behavior of each pair of differentiating characters in hybrid union is independent of

the other differences between the two original plants (Mendel 1866/1996, p. 36).

Be that as it may, it is true that Mendel devised an outstanding experimental design

that allowed him to observe the consequences of the two laws for which he is famous.

This experimental design is probably the major reason for the impact of his work after

1900, when other scientists were studying heredity using an approach that had similarities

to Mendel’s (Kampourakis 2013).

All the controversies around Mendel’s original papers certainly do not dismiss the

huge impact of his work. It just means that this impact resulted from the refraction of his

results and arguments under the lens of the theoretical perspectives of fin-de-siècle

scientists who rediscovered his 1866 paper. This fact is hardly surprising, but deserves

attention, because it makes us ponder on how we tend to read too much in Mendel’s

papers when we cast them against the backdrop of subsequent history. When we examine

the original papers we can echo Olby’s (1985) conclusion: Mendel was not a Mendelian

in the sense of assuming the existence of a finite number of hereditary elements or

particles, but was a Mendelian in the sense of treating hereditary transmission in terms of

independent character-pairs and statistical relations of the progeny of the hybrids as

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approximating the combinatorial series. That is, we do not find in Mendel the mechanism

of heredity established in classical Genetics, but we do find the experimental approach

that would become the foundation of this science. Thus, it is fair to treat Mendel’s work

as a founding source of Genetics (Hart and Orel 1992; Sandler 2000; Falk 2006, 2009;

Kampourakis 2013).

But, interestingly enough, Mendel was not included in the community of scientists

studying heredity in the second half of the 19th century, as mentioned above. This

community was composed by scholars who knew about each other’s works and offered

constructive mutual criticism that led occasionally to changes in their theories

(Kampourakis 2013). Although Nägeli knew about Mendel’s 1866 paper at the time it

was published, he did not give much attention to Mendel’s work (Sturtevant 1965/2001,

Dunn 1965/1991). This indicates that he did not agree with Mendel’s conclusions,

thinking instead that all the offspring of the hybrids was variable (Kampourakis 2013).

Nägeli was studying Hieracium, being unaware that it was an exceptional case, as a

parthenogenetic plant, while Mendel was studying the normal case, found in Pisum.

That’s why Mendel felt confused when he investigated Hieracium, following Nägeli’s

suggestion, only to find results contradicting those with Pisum. But Nägeli also worked

with Pisum from 1866 to 1871, and did not find results that agreed with Mendel’s findings

(Olby 1966).

Nägeli was not the only one in that community of scholars that was aware of

Mendel’s work. Romanes cited Mendel’s 1866 paper in 1881, based on a copy of William

Focke’s book Die Pflanzen-Mischlinge, Ein Beitrag zur Biologie der Gewächse (The

Plant Hybrids, a Contribution to the Biology of Plants), where Mendel’s work is

mentioned. Darwin sent this book to Romanes before reading it. However, Darwin may

have had contact with Mendel’s results, not in his original 1866 paper, but through other

sources. Vorzimmer (1968) argued that Darwin was aware of Mendel’s work, first,

because he was in direct contact with two naturalists who knew it, Nägeli and Hermann

Hoffmann. Second, Vorzimmer calls attention to the entry #112 in Darwin’s Reprint

Collection, a long paper by Hermann Hoffmann, Untersuchungen zur Bestimmung des

Wertes von Spezies und Varietät (An Investigation into the Quality of Species and

Varieties). This was an extensive review of experiments with hybrids, including a critique

of Darwin’s theory of pangenesis. Since Hoffmann’s paper offered a summary of

Mendel’s work, Vorzimmer concluded that Darwin was aware of Mendel’s results. In

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Hoffman’s paper, Darwin was cited four times along the description of Mendel’s work,

what might have called Darwin’s attention.

Olby and Gautrey (1968) noted, however, that Darwin only mentions Mendel’s

experiments with Phaseolus, also reported in Hoffmann’s work. By considering the

written marginalia in Darwin’s handwriting in Hoffman’s paper, these authors stress that

it can only be found up to page 78. They speculate, thus, that Darwin may have jumped

from page 78 to the Schlussrèsümè in pp. 169-171, never reading the reports on Mendel’s

experiments with Geum and Pisum. However, Bizzo (1999) examined Hoffmann’s

brochure in Darwin’s Reprint Collection at the Manuscripts Room, Cambridge University

Library, and discovered that there is marginalia further on in the brochure, near the report

of the results with Pisum, more specifically, an X, in pencil, with three dots and a trace

in the inner space near each angle. He interpreted this scheme as a reference to the 3:1

ratio in the second generation of the hybrids. Further on in the brochure, he found another

cross showing four traces, which he interpreted as possibly a reference to the first

generation of the crossing. This suggests that Darwin may have actually read Hoffmann’s

report of Mendel’s results but had his own interpretation of these findings, which led to

no consequences regarding his own ideas about heredity (see also Bizzo and El-Hani

2009).

Darwin himself performed experiments with Anthirrinum majus (snapdragon) in

which he found a 3:1 ratio between two flower forms (peloric and radial) in the second

generation of the hybrids (Darwin 1868). He recognizes that other scholars had already

reported such results, which he interpreted as a “reversion” in the second generation to

the latent form (radial flower) in one third of the cases. He explains these results in the

last chapter of his book, where he addresses Pangenesis, in a manner that is fundamentally

different from Mendel’s. This is a nice example of how the same experimental results can

be differently interpreted by researchers committed to distinct theoretical frameworks.

Darwin argues that the “prepotency” of the gemmules postulated by his theory of heredity

change according to the circumstances and, thus, the reappearance of the radial flowers

in the second generation was a direct reflex of changing the plant to a soil with a different

fertility.

It is difficult to see, indeed, how Darwin could have used Mendel’s interpretations,

given his reliance on his own theory of heredity, as shown by his exchange with Galton

on the experiments with rabbits performed by the latter, which did not support pangenesis

(Galton 1871). Darwin did not accept the disproof of his theory, arguing that Galton’s

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experimental design, which made use of blood transfusions between different variants of

the same rabbit species, assumed an idea unnecessary to pangenesis, namely, that the

gemmules postulated by the theory were gathered from the blood (Darwin 1871).

Even though some researchers knew about Mendel’s work before 1900, it was

only after his1866 paper was rediscovered that year, being read in an entirely different

context, that his work had any significant impact. Mendel’s paper may have been co-

opted to resolve a priority dispute between Correns and de Vries (Branningan 1979;

Darden 1985; Meijer 1985). Moreover, the story of the rediscovery of Mendel’s work can

be seen as a historical artifact following from the Mendelian geneticists’ exaggeration of

the coincidences between Mendel’s and de Vries’, Correns’ and Tschermak’s findings

(Bowler 1989). This would be a way of stressing that those findings were so obvious that

no careful scientist could ignore them.

Mendel’s work was seen in the turn of the century under a new light resulting from

several ideas: hard inheritance (as opposed to soft inheritance), promoted by Galton and

Weismann, with discontinuous variation, non-blending characters, and no room for the

inheritance of acquired traits; the view that particles inside the cell controlled the

development of characters, increasingly advocated by scholars studying heredity in the

second half of the 19th century and supported by cytologists (Bowler 1989; Kampourakis

2013); and the increasing understanding of the role of chromosomes. The formulation of

Mendel’s laws as we now know them resulted from these developments at the transition

from the 19th century to the 20th century.

It can be enlightening, finally, to assess how different authors interpreted Mendel

differently in order to enlist him to support their own views. Sapp (1990) shows that both

biologists and historians present Mendel as supporting nine different and sometimes

contradictory claims in order to secure his voice as a supporter. Hence, we should be

attentive to biases behind any “Mendelian” label (Allchin 2000). This is certainly the case

of the early use of Mendel as a patron in the beginnings of Genetics, which influenced

how geneticists read Mendel as supporting their own accounts of inheritance, even when

this account was not so clear – to say the least – in Mendel’s original work

When we examine the historical literature, we can see, in sum, how the

interpretation of Mendel’s works and their contribution is highly polemical. In the science

classroom, however, these polemics are entirely absent from the discussion of Mendel’s

achievements and role as the so-called father of Genetics. Considering the changes in

school science that could ensue from taking into account those controversies, we were

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stimulated to examine whether articles targeted at teachers as their audience make them

available for practitioners.

3. Mendel in articles for teachers

In our survey, we considered articles published in journals targeting in-service and

preservice teachers as at least part of their intended audiences. These journals were

located based on our own experience and, also, by asking 12 science education

researchers to suggest journals with this profile. We did not include in this study popular

science magazines, even though teachers commonly make use of them.

The list of journals included: The American Biology Teacher, Journal of

Biological Education, The Science Teacher, School Science and Mathematics, Science in

School, School Science Review, Innovations in Education and Teaching International,

Experiências em Ensino de Ciências (Experiences in Science Teaching), Ciência em Tela

(Science on Screen), Genética na Escola (Genetics in School), Alambique: Didáctica de

las Ciencias Experimentales (Alambique: Didactics of the Experimental Sciences),

Enseñanza de las Ciencias (Science Teaching), Revista Electrónica de Enseñanza de las

Ciencias (Electronic Journal of Science Teaching).

We cannot claim that this is an exhaustive list, since it only includes journals

published in English, Portuguese, and Spanish/Catalan. Nevertheless, this list certainly

includes a broad range of relevant journals, with different missions, audiences, and

publication styles.

When the journals were indexed in databases such as Web of Science® or

Scopus®, we performed searches within with the following keywords: Mendel; Histor*

and Heredit*; Histor* and Inheritance; Darwin and Heredit*; Darwin and Inheritance;

Spencer; Galton; Brooks; Nägeli; Weismann; and Vries. When the journals were not

indexed, we examined the table of contents for each of their issues, with the same

keywords in mind. After we downloaded the papers, we checked if they indeed addressed

Mendel’s contributions to the emergence of Genetics or the works of other scholars who

studied heredity in the second half of the 19th century.

We obtained 29 papers, which are listed in Appendix A, distributed among the

following journals: The American Biology Teacher, 9; Enseñanza de las Ciencias, 5;

Genética na Escola, 5; The Science Teacher, 4; Journal of Biological Education, 2;

Alambique: Didáctica de las Ciencias Experimentales, 1; School Science and

Mathematics, 1; Science in School, 1; Ciência em Tela, 1.

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When examining the papers, we were interested in how they describe the historical

circumstances and goals of Mendel’s work; whether they attributed the laws of

segregation and independent assortment and the idea of hereditary particles as potentials

for traits to Mendel’s original work; whether and how they consider changes and

controversies in the interpretation of Mendel’s work or appraise the views about Mendel

disseminated in school science; and, finally, if they consider scientists working on

heredity during the second half of the 19th century.

Table 1 presents an overview of the papers examined in this study.

Table 1: Overview of articles for teachers addressing Mendel’s work. (at the end of the file)

3.1. Myths about Mendel in school science

In a number of papers, we find just a small amount of information regarding

Mendel, typically including the claim that his work was the first milestone in the history

of Genetics and ascribing the idea of hereditary particles and/or the laws of segregation

and independent assortment to Mendel’s original 1866 paper. Some papers explicitly aim

at providing a discussion of educational, historical and/or epistemological issues related

to Mendel’s and other scientists’ works (e.g., Kritzky 1973; Hedtke 1974; Corcos &

Monaghan 1985; Huckabee 1989; Allchin 2000; Heppner 2001; Bizzo & El-Hani 2009;

McComas 2012a,b), while others offer comments on those issues while focusing on a

variety of other topics (e.g., Jiménez-Aleixandre & Fernández Pérez 1987; Banet &

Ayuso 1995; Ayuso and Banet 2002).

One of the major problems in how Mendel is treated in school science, also echoed

in part of the papers discussed here, is the tendency to romanticize or idolize great

scientists, distorting in this manner how science really develops as a social enterprise. It

is important, then, “to sharpen the skills of teachers in considering the histories of science

that enter the science classroom” (Allchin 2000, p. 638). The way Mendel’s case is

presented in school science can be seen, thus, as a symptom of a more general difficulty

in the use of history in science education. As in the case of other scientific developments

(for instance, the theory of natural selection or classical mechanics), the construction of

a theory of heredity in the second half of the 19th century, which culminated in classical

Genetics, is explained as if it was a one-man work, and not the outcome of a scientific

community working on the topic (see Kampourakis 2013).

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Mendel’s case is particularly important here, because even though history of

science is not often present in most biology texts, Mendel is usually mentioned. It is

consequential, thus, to critically appraise how Mendel is portrayed in school science, as

some of the papers do (e.g., Corcos & Monaghan 1985; Allchin 2000; Banet & Ayuso

1995; Ayuso & Bannet 2002). The moral undertones in the descriptions of Mendel’s

accomplishments in school science are quite clear and connected with a certain view

about the nature of science (NOS) (Allchin 2000). The myth that Mendel was working in

isolation inside a monastery adds to his portrayal as an exemplary scientist, who sought

only truth, not fame or wealthy. Mendel is described as being capable of choosing the

right organism to study, while his other experiments, such as those with Hieracium, which

did not replicate his results with peas, are simply forgotten. He is also the paradigm of a

quantitative scientist, who was hard-working enough to patiently count peas for many

generations over many years. In a romantic description of scientific work, Mendel was

supposedly neglected by peers who failed to appreciate the significance of his work. Thus,

Mendel's rediscovery becomes an epic story of a man who won a battle after being almost

forgotten, buried in oblivion. Mendel is often portrayed in school science as “an ideal

type of scientist wrapped in monastic and vocational virtues” (Sapp 1990). This is the

mythic Mendel (Allchin 2000).

Corcos and Monaghan (1985) also discuss a number of myths about Mendel’s

experiments. They are concerned with their presentation without any historical

perspective in textbooks, which only give a modern interpretation based on discoveries

made long after Mendel’s papers. Even though they regard this approach acceptable if

one wants to teach only the basic rules of classical Genetics, they regret that it does not

offer the students (and, for that matter, the teachers) a chance to understand Mendel’s real

contribution or those of his followers. Among the myths concerning Mendel discussed by

them, we find (i) that one can see Mendel’s laws as taught today in his writings; (ii) that

Mendel thought that dominance was always observed; (iii) that he discovered the famous

“Mendelian” ratio, 9:3:3:1; and (iv) that his experimental results showed that the seven

pairs of characters investigated were inherited independently. In particular, they stress

that the laws of segregation, independent assortment, and dominance are developments

posterior to Mendel, attributed to him because we tend to read back in his work our own

conceptual structures, shaped by learning about classical Genetics.

As Allchin (2000, p. 634) discusses, those reading the original paper over a

century later are often impressed with its clarity and modern style, an immediacy that is

15  

deceptive because we are in fact reinterpreting it in our own terms. It is important to

consider in school science, then, that interpreting Mendel involves understanding his

purposes and the context in which he wrote, and, also, seeing how geneticists since

Mendel have interpreted, and sometimes transformed, his work. Nevertheless, biology

texts do not offer much help here, since they often poorly represent or misrepresent

Mendel’s story and contributions.

This deceptive reading of Mendel’s work is indeed found in some papers

examined here, for instance, those in which the laws of segregation and independent

assortment are attributed to Mendel’s original work just as they stand now (e.g., Codina

2005, Miyaki et al. 2006, Ferreira et al., 2010, Offner 2011, Araújo et al. 2012). In other

papers, however, the controversy around the presence of those laws in his work is taken

into account (Jiménez Aleixandre & Fernández Pérez 1987; Banet & Ayuso 1995; Ayuso

& Banet 2002).

Some papers also put into question the presence of the idea of hereditary particles

in Mendel, or at least claim that this idea is not clearly expressed in his works, since

Mendel refers to the separation of characters, not of underlying factors (e.g., Corcos and

Monaghan 1985; Heppner 2001; Bizzo and El-Hani 2009). Others simply ascribe this

idea to Mendel (e.g., Miyaki et al. 2006; Melville and Fazio 2007; Madden 2007; Colburn

2007; McBride et al. 2009; Passmore et al. 2009; Offner 2011; Bonner 2011; Araújo et

al. 2012).

Indeed, adopting a notation employed by Nägeli, Mendel used symbols that

represented the characters present in each individual, not pairs of factors or “genes”

(Corcos and Monaghan 1985, p. 235). This reinforces the idea that Mendel worked out

his results in terms of characters, not of invisible determiners of those characters.

However, this is also controversial. Campbell (1985) maintains that Mendel’s

mathematical treatment suggests that he was indeed thinking in terms of pairs of

characters, employing, say, A instead of AA just because in combinatorial theory each

element is represented a single time (unless one is dealing with permutations).

Another idea put into question by Corcos and Monaghan (1985) is that Mendel

showed that the seven pairs of characters he worked with were inherited independently.

Only three of the seven traits were involved in the dihybrid and trihybrid experiments

whose results Mendel communicates in his 1866 paper: color of the seed albumen; seed

shape; and color of the seed coat. Even though Mendel did not report the results of his

dihybrid crosses involving the other traits, he stated that he carried out those crosses,

16  

obtaining approximately the same results (Mendel 1866/1996, p. 18). Corcos and

Monaghan stress that the word “approximately” is important in Mendel’s report because

independent assortment of characters will not happen if the genes are located in

homologous chromosomes, unless they are very far apart from each other. After

Lamprecht (1961), it was established that three of the traits originally studied by Mendel

were associated with genes located on one chromosome, and two, with genes situated on

another, while the two other genes are on different chromosomes. It is another myth often

found in textbooks, thus, that the seven traits chosen by Mendel were associated with

genes on different chromosomes. As Corcos and Monaghan remarks, it would be

interesting to have Mendel’s results on the crossing experiments involving dihybrids

showing differences in length of stem and pod shape, because it is very likely that they

did not conform to the idea of independent assortment. After all, they are associated with

genes located on the same chromosome only 13 map units apart. If we consider Mendel’s

results for the trihybrid cross he reports in his paper, the genes associated with the color

of the seed coat and the color of the seed albumen are on the same chromosome, but too

far apart to show linkage. As they sum up, “Luck was definitely on the side of Mendel”

(Corcos and Monaghan 1985, p. 236).

A number of papers discuss how Mendel’s 1866 article was interpreted after its

rediscovery, considering the changes in its understanding as it came to be seen under

different lens (e.g., Corcos and Monaghan 1985; Jiménez Aleixandre and Fernández

Pérez 1987; Allchin 2000). Allchin, for instance, considers how classical geneticists

recast Mendel’s modest “law of hybridization” as a general scheme of heredity. Suitably

reinterpreted, Mendel’s work became “a guide - a virtual touchstone” (Allchin 2000, p.

635) in the beginning of the 20th century, when the framework of classical Genetics was

constructed. It could play this role because of the experimental design he developed and

classical Geneticists substantially extended (Olby 1985), while the ideas of particulate

inheritance and the laws of segregation and independent assortment seemed to be read

back in Mendel’s paper by his successors.

3.2. Mendel and other scientists interested in heredity in the second half of the 19th

century

Scientists working on heredity during the second half of the 19th century are

scarcely mentioned in the papers discussed here. Nägeli is mentioned in some papers

(e.g., Kritzky 1973; Jiménez Aleixandre & Fernández Pérez 1987), but without a focus

17  

on his theory of heredity. Darwin’s and Galton’s contributions are also addressed, with

more detail than Nägeli’s. Other scientists involved in studies about heredity are not

mentioned. Even though some papers, like Bizzo and El-Hani (2009) and McComas

(2012a,b), offer at least a glimpse at the social construction of ideas about heredity in the

19th century, overall the papers do not provide an understanding of how ideas about

heredity were developed by the scientific community at that period.

Bizzo and El-Hani (2009) comment about a small but important change in one of

the phrases in Darwin’s chapter on inheritance in the second edition of Variations (1875).

In the first edition, Darwin writes:

It is therefore not surprising that every one hitherto has been baffled in drawing up general

rules on the subject of prepotency (Darwin 1868, p. 71),

Darwin claims, thus, that no one had already dared to put forward a general theory

to heredity. In the second edition, however, this statement reads differently:

It is therefore not surprising that no one hitherto has succeeded in drawing up general rules

on the subject of prepotency” (Darwin 1875, p 47, emphases added).

This suggests that he was aware of theories of heredity proposed by his

contemporaries, but judged them as not being successful in explaining the matter of

prepotency.

McComas published two papers providing an extensive treatment of the theory of

pangenesis (McComas 2012a,b), in which he not only describes the story of the theory,

but also discusses lessons on NOS we can derive from it. Moreover, he provides some

discussion on Galton’s ideas about inheritance. He shows how pangenesis accounted for

a variety of fascinating phenomena (besides inheritance and the source of new variation,

also regeneration, reversion or atavism, among others), even though it is not an accurate

argument. As he writes, “pangenesis does explain how inheritance works (all before the

discovery of Mendel’s laws, the gene, and DNA)” (McComas 2012a, p. 89).

Among the NOS ideas that can be illustrated by pangenesis, McComas (2012b)

includes the need for empirical evidence, the use of inductive reasoning, the role of

creativity in science, the role of bias and subjectivity (or, alternatively, the lack of

18  

complete objectivity), social and personal influences on scientific work, and the tentative

and self-correcting character of scientific knowledge.

3.3. Mendel and Darwin

McComas offers a single comment on Mendel’s work in his first paper on

pangenesis:

Ironically, the basic rules of inheritance were available during Darwin’s time through the

work of Gregor Mendel. However, there is no evidence that Darwin had access to the

obscure journal of the Brno (Brunn) Natural History Society (sic), in which Mendel

published in 1866 (McComas 2012a, p. 89).

He mentions, then, that Darwin might have owned at least two books citing

Mendel’s work, and concludes:

However, he likely did not read or sense the importance of these ideas, nor is there any

assurance that Darwin would have understood the mathematical argument on which the

nascent science of genetics was founded (McComas 2012a, p. 89).

Indeed, Darwin probably never had access to the Brüun Natural Science Society

journal, even though it was distributed to several universities and scientific societies.

McComas was not aware, however, of even more convincing evidence that Darwin may

have read accounts of Mendel’s work, as we discussed above, and did not take into

account the finding of the 3:1 ratio by Darwin in his own investigations (Darwin 1868).

Finally, it is reasonable to assume, indeed, that Darwin might have had difficulties with

Mendel’s approach, either by the use of mathematical arguments (which, as Darwin

himself acknowledged, were not much under his grasp) or by the tensions with his own

theorization about heredity. But this may contradict what is suggested by the following

passage in the second part of McComas’ work:

Although Darwin was a contemporary of Gregor Mendel, his pea plant experiments were

not well known, leaving Darwin with no alternative but to develop his own explanation for

inheritance (McComas 2012b, p. 151).

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After all, this suggests that, if Darwin had known Mendel’s work – as he may have

–, he would not develop pangenesis as an alternative theory. In fact, he stuck to his theory

even when he found similar results to those obtained by Mendel, rather interpreting them

in accordance to pangenesis (see below).

Still concerning the relation between Mendel and Darwin, Bonner (2011) ascribes

to Mendel a view shared with current students, namely, that Genetics has no role in

evolution, resulting from the misconception that alleles are stable and cannot change. He

echoes an argument put forward by Callender (1988), who claims that Mendel’s major

goal was to show that descent with modification by means of natural selection was not

possible. However, Mendel only mentioned Darwin in his 1870 paper on Hieracium,

where he does not express any opinion about Darwin’s theory. In this respect, we agree

with Fairbanks and Rytting (2001) that there is not strong evidence that Mendel either

opposed or supported Darwin.

Bizzo and El-Hani (2009) discuss how the idea that Mendelian genetics should be

explained to students before evolution in the high school curriculum is rooted in historical

and epistemological assumptions about the relations between Mendel’s and Darwin’s

works. The claim that Darwin was unaware of Mendel’s work is found in many sources

(e.g., PBS 2001), including scientific works (e.g., Mayr 1991), textbooks (e.g., Raven et

al. 2004; Campbell & Reece 2008) and, also, the papers discussed here (e.g., Kritzky

1973, 1974). As Bizzo and El-Hani discuss, it is often believed that Darwin could have

carried out a larger theoretical work if he had more information about Mendel’s research

and the laws of heredity. In these terms, Darwin’s pangenesis theory is ignored and the

supposed lack of a theory of heredity is thought to result in faults in the Darwinian

evolutionary theory. School would have to provide, thus, a prior background on heredity,

so that students might avoid those faults.

It is even claimed that Darwin would make major advances toward building the

synthetic theory of evolution if he had the opportunity to know Mendel’s work. Rose

(1998), for instance, argues that if Darwin had read carefully Mendel’s 1866 paper,

evolutionary biology could have been anticipated in at least three decades. This is

certainly not the case, given the convoluted history of the evolutionary synthesis (Bowler

2003). Therefore, we have here another myth that thrives not only in school science, but

among scientists themselves. Its origins are traced by Bizzo and El-Hani to William

20  

Bateson’s influential book Mendel’s principles of heredity: A defense (1902). There we

read:

Had Mendel’s work come into the hands of Darwin, it is not too much to say that the history

of the development of evolutionary philosophy would have been very different from that

which we have witnessed (Bateson 1902, p. 39).

In a later edition of the book, Bateson repeats the same statement (p. 31), but also

adds another similar argument:

I rest easy in the certainty that had Mendel’s paper come into his [Darwin’s] hands, those

passages [about the views of evolutionary progress through blending] would have been

immediately revised (Bateson 1909, p. 19).

These statements should be interpreted in the context of the controversies between

Bateson and the biometricians (Olby 1989; Bowler 2003). Bateson was trying to bring

Darwin to his side of the debate: if he had known Mendel’s work, Bateson is suggesting,

he would support his position, not that of Galton and his followers.

The fact that we now see, retrospectively, Mendelism and Darwinism as

complementary theories does not mean that their potential synthesis could be foreseen

either by Darwin or by the early geneticists and biometricians. Symptomatically,

Mendelian genetics and Darwinism were understood as rival theories at the beginning of

the 20th century.

Moreover, Bizzo and El-Hani (2009) argue that perhaps Darwin was aware of

Mendel’s work, but, more than that, obtained results showing the 3:1 ratio in his own

investigations. Yet, he did not get any closer to what would become the evolutionary

synthesis. Quite naturally, Darwin used his theory of pangenesis to interpret the results

he obtained with snapdragons, considering that gemmules could appear in a “prepotent”

or a “latent” form and, also, could acquire (or lose) vigor, becoming more or less

prepotent. This would explain why, after some generations, there would be either a

“reversion” to the parental stock (what explained the 3:1 ratio), or the latent gemmules

would disappear. In the last chapter of Variations of animals and plants under

domestication (Darwin 1868), Darwin argues that the “prepotency” of the gemmules

21  

changes according to the circumstances, from generation to generation. The appearance

of radial flowers in the snapdragon is interpreted, then, as a direct reflex of changing the

plant to a soil with different fertility. This is quite different from Mendel’s model, even

if we do not consider any talk about underlying factors or elements, since gemmules

would not only change continuously, but also mix with one another so that the characters

they determined would blend in the offspring. Mendel stressed, in turn, that characters do

not blend in the offspring. In more recent terms, unknown to either Darwin or Mendel,

Darwin was working within a model of “soft inheritance”, allowing for the inheritance of

acquired characters, and Mendel, with one of “hard inheritance” (Mayr 1982). They were

working within different theoretical frameworks, and Darwin could not see how the ideas

found in Mendel’s 1866 paper would fit together with his own theories (Bizzo and El-

Hani 2009, p. 111).

Historical arguments about what Darwin would have accomplished if he knew

Mendel’s work do not hold. More than that, they are misleading, and cannot be used to

support a curricular proposal of teaching Genetics before Evolution. To show Mendel’s

work as directly connected with Darwin’s does not provide an epistemological bypass to

the students. The idea underlying that curricular proposal is that, if students begin to study

evolution with an additional knowledge that Darwin lacked in his time, namely

Mendelian genetics, school science would provide a ‘fast lane’ in terms of curriculum

design that might favor understanding of biological evolution. For Bizzo and El-Hani,

this argument is fallacious, lacking sound evidence in either historical or cognitive

grounds.

Mendel, in turn, was probably aware of Darwin’s work. As Kritzky (1973)

discusses, he was no friar in isolation, and could hardly have ignored all the controversy

around the Origins of species. Besides, a major figure in the Brünn Natural Science

Society, the botanist and geologist Alexander Makowski, talked with enthusiasm about

Darwin and the Origin in one of the meetings in which Mendel read his paper in 1865

(Iltis 1932/1966). Finally, a copy of Origin was available at the library of the monastery,

where it can be found today, with notes in Mendel’s handwriting.

The fact that Mendel knew about Darwin leads Kritsky’s to some hardly justifiable

concerns about Mendel’s reputation:

The comment is usually made that if Mendel had contacted Darwin, perhaps evolutionary

theory would have been different. This thought – that Mendel could have done more to

22  

push the movement of man’s knowledge about his biologic existence – is intriguing and

could put Mendel in a different perspective by questioning the sincerity of his work

(Kritzky 1973, p. 477).

But given that Darwin and Mendel were working under different theoretical

frameworks, it is not obvious or even likely that Darwin would change his theory because

of Mendel’s results, as discussed above. Kritzky also argues that Mendel was inclined to

believe in evolution but was skeptical about natural selection. He speculates that given

Mendel’s position in the monastery, it would be better for him to stay quiet concerning

evolution. Some indications of Mendel’s mistrust in evolution are mentioned by Kritzky.

For instance, Mendel would have argued in his 1866 paper that Gärtner’s inability to

transform one species into another was proof of some barrier around the species. But

Kritzky is distorting what Mendel writes, since he rather presents this conclusion as

Gärtner’s and indicates that he does not accept it unconditionally:

Gärtner, by the results of these transformation experiments, was led to oppose the opinion

of those naturalists who dispute the stability of plant species and believe in a continuous

evolution of vegetation. He perceives in the complete transformation of one species into

another an indubitable proof that species are fixed with limits beyond which they cannot

change. Although this opinion cannot be unconditionally accepted we find on the other

hand in Gärtner’s experiments a noteworthy confirmation of that supposition regarding

variability of cultivated plants which has already been expressed (Mendel 1866/1996, p.

39).

Kritzky also mentions Niessl’s allegation that Mendel would have said that nature

does not “modify the species in any way”. The same source mentions that evolution

interested Mendel, but he felt the theory was incomplete. However, how can Kritzky

conclude, after putting these pieces of information together, that Mendel was far from

being an antievolutionist and could be even inclined to accept evolution? The only

evidence he adduces for this conclusion is a passage from a letter sent by Mendel to

Nägeli, which is, for him (Kritzky 1973, p. 479), “nothing more than a condensed version

of Darwinian evolution”:

23  

If such be the real state of affairs, spontaneous hybridization in Hieracium must be ascribed

to temporary disturbances which if frequently repeated or persistent must even lead to the

disappearance of the species in question, whereas one of another more favourably

organised hybrid offspring better adopted to the extant telluric and cosmic conditions might

succeed in maintaining itself in the struggle for existence and might thus persist for long

periods of time, until at length overtaken by the same fate (as quoted by Iltis 1932/1966, p.

204).1

In view of these arguments, we can still rest content with the conclusion that no

strong evidence is available that Mendel either supported or rejected Darwin’s theory (or,

for that matter, evolution) (Fairbanks and Rytting 2001).

Another question posed by Kritzky is whether Mendel failed to recognize the

importance of his own work. He mentions the rather unlikely possibility that Mendel

could see his work as just a hobby, pointing that townspeople in Brünn would comment

with visitors that they did not think there was anything serious about Mendel’s

experiments. He also mentions a report by a salesman for plants and supplies, Eichling,

who asked Mendel how the hybrids were obtained (Eichling 1942). Mendel replied that

it was just a little trick, avoiding elaborating on his experiments. Dodson (1955)

comments that Eichling believed that Mendel said so because he did not want bore his

guest. Kritzky puts this explanation into doubt by pointing that Mendel would talk to

visitors with great joy about his hybrid bees, and it would be difficult to explain why he

would talk about one project and not the other. But here more information on the timing

of the events is crucial. Eichling met Mendel in 1878, a long time after he had abandoned

his scientific studies to dedicate to his duties as abbot of the monastery. It is

understandable that he would not be so excited to go over the “long story connected with

it (the hybrid pea)” which “would take too long to tell” (cited by Eichling 1942, p. 245).

Kritzky himself cast doubt on the hobby explanation, since he also argues that

Mendel knew he had discovered something major. After all, Mendel often told Gustav

von Niessl, a member of the society, that his time would come (Iltis 1932/1966). Also, in

a letter to Nägeli, Mendel showed his concerns about publishing his results in a consistent

manner, with more than one isolated experiment, since theys were not easily compatible

                                                            1 A different translation is offered in the first publication in English, which appeared in Genetics (Mendel 1950, p. 34). The letter was written in November 18th 1873. It is the last letter sent by Mendel to Nägeli.

24  

with the contemporary scientific knowledge (Mendel 1950, p. 4, the letter was written in

April 18th 1867).

When considering whether Darwin knew of Mendel’s work. Kritzky claims that

... the evidence indicates that Darwin may have read the name Mendel, but he probably

never knew anything about Mendel’s work (Kritzky 1973, p. 479).

In a later paper, Kritsky (1974) insists on the claim that Darwin was not aware of

Mendel’s work, since it would have looked important to him. After all, when Mendel’s

paper was published, Darwin was working in the book where he presented his theory of

pangenesis, Variations (1868).

In an answer to Kritzky, Hedtke (1974) claims that Darwin knew about and

understood the results of Mendel’s work on plant hybridization. However, Darwin would

have concluded that Mendel’s experiments were in contradiction with his theory.

Hedtke’s case for Darwin knowing about Mendel is based on the assumption that he might

have read Foche’s book Die pflanzenmischlinge, which addresses Mendel’s work.

Nevertheless, we know now that this book was not read by Darwin. For Hedtke, the

incompatibility between Darwin’s theory of evolution and Mendel’s work follows from

the commitment of the former to variability and the latter to constancy, given Mendel’s

finding of constant numerical ratios among the types produced by hybridization. For this

author, the members of the Brünn Natural Science Society would have evidently grasped

the obvious contradiction between Mendel’s and Darwin’s work, both presented at the

same meeting.

In Kritzky’s (1974) answer, he argues that, if Mendel’s experiments were in

contradiction with evolution, we would need to explain why Mendel did not join the

debate on the topic. His speculation is that Mendel did not think they were contradictory,

but rather provided an insight into the mechanism of variation. This is very unlikely since

Mendel’s goal was not to develop a theory of heredity and variation, as discussed above.

Several other explanations can be put forward to justify why Mendel did not engage in a

discussion on evolution. We can consider, for instance, that he was indeed working in the

tradition of hybridists and might not be particularly interested in that topic. Moreover,

after he became an abbot in 1868 his increasing administrative responsibilities eventually

demanded that he largely abandoned his scientific work (Olby 1985).

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3.4. Misconceptions about dominance

Misconceptions about dominance are discussed in six of the papers examined. In

Allchin (2000), to discuss these misconceptions is the main goal. His intention is to mend

the concept of dominance we attribute to Mendel, even though he never held it (p. 638).

His concerns hinge upon the fact that dominance is not a causal property, as usually

portrayed, but a pattern of relation between characters (and their determinants).

Moreover, although it is not the more frequent pattern, it is presented as such in school

science, overshadowing other patterns more common in nature, such as incomplete

dominance.

Other papers examined here shares the same worries, such as Corcos and

Monaghan (1985) and Mingroni Netto (2012). This latter author argues that, from a

molecular point of view, it is necessary to analyze each case separately, considering if it

is a case of dominance, incomplete dominance, codominance. To apply these concepts,

one needs to consider how the phenotype is defined in the genetic analysis and, also, that

the effects of an allele over a phenotype depend on a complex network of molecular

phenomena. Several cases are discussed in the paper in a useful manner to science

teachers. Regarding our main topic here, there are only two relevant comments about

Mendel in the paper, namely, that the terms “dominance” and “recessiveness” appeared

for the first time in Mendel’s works, and the transmission of hereditary factors were

studied by Mendel through crossings between pea plants. In the former case, there is a

slight imprecision, since Mendel did not use the substantives at stake, but only the

adjectives “dominant” and “recessive”. In the latter, there is the controversy about

whether Mendel really worked out his results in terms of factors, as discussed above.

Corcos and Monaghan (1985) also criticize the idea that dominance is the general

rule in the relation between characters, highlight the importance and frequency of other

patterns. Even though this idea is often traced back to Mendel’s original works, he never

assumed that one character was always dominant over another. Although the seven pairs

of characteristics chosen by Mendel in his Pisum study are examples of complete

dominance, he was aware that this is not a universal phenomenon. In his 1866 paper he

mentions an eighth trait, flowering time, which shows incomplete dominance. It was one

of his rediscoverers, Hugo de Vries, who generalized the phenomenon of complete

dominance, ascribing to it the status of a law. However, this was not consensual among

his fellow scientists. Another rediscoverer, Carl Correns, stated that he could not

26  

understand why de Vries assumed dominance as a general rule, after finding many traits

of peas and other plants in which dominance does not hold (Corcos and Monaghan 1985).

It is interesting to notice that misconceptions about dominance are found in one

of the papers (Bonner 2011), in which dominance is described as the most common

pattern of relation between phenotypes. In the same paper, there is another misconception,

namely, that there would a general mechanism for dominance in molecular or cellular

terms, according to which “generally, alleles with more activity are dominant to alleles

with less activity” (Bonner 2011).

The prevalence of dominance and, broadly speaking, Mendelian genetics in

Genetics teaching is related by Allchin to Mendel’s authority:

I contend that the conceptual organization reflects Mendel’s authority, even where we

know it misleads students. The problem is thus embedded in our very respect for Mendel.

Historically, geneticists and teachers have seemed unable to separate dominance from the

image of Mendel as a great scientist. Biologists have revered Mendel, and hence also the

version of genetics that now bears his name (Allchin 2000, p. 635).

Mendel used the adjective "dominant" as a linguistic tool, not intending to advance

any claim about inherent properties of the characters (Allchin 2000). He never described

a general principle or relationship between characters and, accordingly, never introduced

"dominance" as a noun (or even a verb, which could hint at ascribing to dominance the

character of a causal property). Mendel never claimed, for example, that a trait would

appear in the hybrids because it was dominant and he did not ascribe the adjective

“dominant” to factors or elements that could be potentials for trait.

Among the problematic conceptions related to dominance discussed by Allchin, a

prominent one is indeed its treatment as a causal property that might explain why a hybrid

shows a given trait. In addition to this common usage, the term "dominance" is now

applied to genes, or alleles, and thus its reference was shifted from phenotype to genotype,

something that also facilitates the misconception of “dominance” as causal. As the

historical discussion above shows, our current “Mendelian" concept of dominance was

not Mendel’s at all. After all, there is no clear or at least uncontroversial statement in

Mendel’s original work of the idea of factors underlying the manifestation of traits. In the

absence of this idea, dominance does not gain the causal overtones that currently mark

27  

the use of the term. This shows how consequential it is to ascertain if Mendel was talking

only about characters, or also about underlying potential to characters, or, if we frame this

argument in contemporary terms, if he was talking only about phenotypes, not about

genotypes.

The difficulties faced by teachers when explaining dominance are also considered

in the papers (Allchin 2000, Heppner 2001). A curious account of the reasons for these

difficulties is provided by Heppner, who argue that Mendel “may not have actually used

the word, nor any derived concepts, in his original paper” (p. 150). Thus, the attribution

of the term “dominance” to Mendel is put into question by this author, who calls attention

to the fact that the terms “dominant” and “recessive” were introduced into English by

Bateson (1900), who also applied it to genetic characters. Now, it may evidently come to

the mind of many readers that these terms appear in Mendel’s work itself. We should ask,

then, about the translation of his 1866 paper from German into English. In the first full

English translation of the paper, sponsored by the Royal Horticultural Society, we find

no identification of the translator, but the article contains both an introduction and

footnotes by Bateson, Mendel’s first English-speaking champion. Thus, it is likely that

he supervised this translation, if he did not actually make it himself (Heppner 2001).

Indeed, the translation is often attributed to Bateson.

Heppner calls attention to the first occurrence of the word “dominirende” in

Mendel’s original paper, which was translated as “dominant” in the English version. He

also mentions that the acceptance of “dominant as applied to characters resulted from a

series of papers published by Bateson. Then, in 1916 Bridges joined “dominant” with

“gene”, “setting the stage for later confusion” (Heppner 2001, p. 150).

A contemporary general German-English dictionary (Wessley 1896, quoted by

Heppner 2001) is examined by Heppner, who finds that it offers only “dominant” as a

translation of “dominirende”. But – he stresses – a later encyclopaedic dictionary (Muret

and Sanders 1974, quoted by Heppner 2001) also permits “predominant”, referring to

number or proportion. He claims, then, that the right translation for “dominirende” would

be “predominant” rather than “dominant”, building his case on this finding, as well as on

the argument that Mendel did not discuss mechanisms of inheritance in his paper.

However, his arguments are not strong enough, since he is referring to a dictionary

published almost a century after the English translation! To build a stronger case, he

would need to show a contemporary dictionary with another translation to “dominirende”.

In fact, we examined a 1910 edition of precisely the same encyclopaedic dictionary

28  

Heppner uses in the 1976 edition, Muret and Sanders. There we did not find the word

“dominirende”, but the corresponding verb “dominieren”, with the meanings “to

domineer” and “to lord it” (Muret-Sanders Encyclopaedic English-German and German-

English Dictionary, Baumann 1910, p. 267). We also find there, curiously, the word

“dominante”. More importantly, Heppner’s argument cannot be supported, since the

meaning “predominant” for “dominirende” does not appear in the very same dictionary

he used, in an earlier edition, published only 9 years after the English translation of

Mendel’s 1866 paper.

Moreover, it is not clear that Mendel’s focus on the distribution of characteristics,

not on mechanisms of inheritance, can ground Heppner’s argument that the concept of

dominance is not found in his work. It is possible to understand Mendel as claiming that

the trait that all the first generation of the hybrids exhibited would always be manifested

when paired with the other trait, which he called “recessive” (the same word in German

and English), with no reference in fact to the mechanism of transmission or mode of

inheritance. Notice, also, that this interpretation immediately makes it clear what he meant

by “recessive”, something that is not so clear if “dominirende” is assumed to mean

“predominant”.

3.5. Mendel in a pedagogical context

Finally, some papers discuss Mendel’s works in a pedagogical context. Jiménez

Aleixandre and Fernández Pérez (1987) summarizes controversial points related to

Mendel’s 1866 paper and describes an experience of using an extract as a primary source

in Genetics teaching at the High School and University level.

They stress that Mendel’s work was “rigorous and innovative” for several reasons,

such as the following: his research program seems to be grounded on the conjecture that

there are natural laws in the biological realm, while the existence of such laws was at the

time only accepted in the physical sciences; he expressed in quantitative terms the

proportions of individuals showing different characters; he introduced the concepts of

“dominant” and “recessive”; his experimental design was based on a set of theoretical

hypothesis, made use of controls, and involved a large number of tests (given Mendel’s

concerns with biases and the influence of sample size on the results).

Their proposal for classroom use include extracts from Mendel’s 1866 paper and

from a study on history, philosophy, and science teaching, used to provide historical

context to the reading of Mendel (Oldham and Brouwer 1984). The goals are to highlight

29  

aspects of scientific methodology, such as the existence of open questions and the

importance of theoretical hypotheses; to promote a critical attitude among students and

demystify scientific discoveries; to situate the discovery of inheritance mechanisms in a

historical context; and to increase students’ familiarity with original scientific texts. A

guide for students’ work with the text was made available, asking them to list the

theoretical and methodological errors that caused the failure of other hybridists2,

according to Oldham and Brouwer (only the High School students); to enunciate the

relevant methodological aspects of Mendel’s experiments that appear in the extract of his

paper; and to mention if they found something in Mendel’s text that disagrees with current

genetic knowledge. Finally, they briefly mention some results obtained with High School

and University students, for instance, that the former mostly mentioned features that were

explicit in the text, while the latter also mentioned implicit aspects, such as the

formulation of a hypothesis or the use of a symbolic notation. Jiménez Aleixandre and

Fernández Pérez sum up their results by stating that they show the need of improving not

only the students’ knowledge about ways of making science, but also their reading

capacity.

In a paper that analyzes some causes of learning difficulties in Genetics at

secondary education, reports evidence on Spanish students’ ideas about inheritance, and

proposes some didactic alternatives for Genetics teaching, Banet and Ayuso (1995)

consider the central role given to Mendel’s laws in Genetics textbooks and, consequently,

in school science. They comment that, although other researchers (e.g., Jiménez

Aleixandre & Fernández Pérez 1987) highlight the development of a historical approach

to Genetics as one advantage of introducing the study of heredity by means of Mendel’s

laws, the textbooks they examined do not reap the profits of this approach. This is a

consequence of the limited view on Mendel’s work offered by them:

Most of the analyzed textbooks and, consequently, many teachers limit themselves to

present Mendel’s works as the first milestone in the history of Genetics, and then go on to

address other aspects (Banet and Ayuso 1995, p. 140).3

                                                            2 This may be questioned from the standpoint of the necessity of understanding the hybridists’ decisions in the historical context in which they worked, instead of judging them to be errors from the perspective of the present, or even of Mendel’s subsequent work. 3 All the passages in Spanish were translated into Portuguese by the author of the present paper.

30  

They also consider the controversies about the interpretations of Mendel’s work,

even though they mention only one side of the debates, quoting Corcos and Monaghan’s

(1985) argument that textbooks are to a great extent responsible for many myths

surrounding Mendel and his work.

4. Concluding remarks

Mendel’s contributions are usually addressed in textbooks and, probably, in

classrooms around the world as if it was clearly established that he proposed the laws

named after him in a formulation close to how they are currently presented, appealing to

invisible factors underlying phenotypic traits, which are seen as the heritable potentials

for those traits, and would in due time be known as genes. In these terms, the distinction

between phenotype and genotype would be found in Mendel’s work, even if not so clearly

as it would become in the first decade of Mendelian genetics. Thus, Mendel is regarded

as the father of Genetics because he supposedly presented in his work the same

mechanism of heredity established by this science, and not only because we find there the

experimental approach characteristic of the new science that would emerge in the turn of

the century. However, while it is not controversial that Mendel is indeed a founding

source of Genetics due to the latter reason, it is very controversial in the historical

literature whether the former interpretation is really supported. In this paper, we assume

that it is hard, to say the least, to provide convincing grounds to an interpretation of

Mendel’s 1866 paper that comes close to the subsequent formulation of a mechanism of

heredity, dependent as it is on the distinction between genotype and phenotype, only

introduced in Genetics with Johannsen’s work in the end of the first decade of the 20th

century. We also explicitly state that this does not dismiss the huge impact of Mendel on

classical Genetics, but shows how the reinterpretation of his work by fin-de-siècle

scientists was needed for this impact to unfold.

Given the contributions of history of science to put the mythic Mendel into

question in the science classroom, bringing school science closer to the controversies

around the interpretation of his work, it was interesting to examine the situation in papers

published in journals that target teachers. Unfortunately, we found in many papers (17

out of 29) the same superficial presentation of Mendel’s work, with the same

interpretation typically found in textbooks. Most of these articles (with exceptions such

as Offner 2011) address other topics, usually pedagogical innovations, and seem to

reproduce less informed ideas about Mendel’s contribution found in other sources, such

31  

as textbooks. However, we also find 12 articles that provide more informed and critical

discussions of Mendel’s work and how it was (re)interpreted in subsequent years. An

important factor for this more informed discussions was the availability of a rich literature

on Mendel in journals devoted to the history of science (with some works also appearing

in educational journals), which was put to use by the authors of these papers. The

examination of Mendel’s original articles also played a role in the construction of a more

sophisticated appraisal of his work.

Nevertheless, a minority of papers addressed other scientists involved in 19th

century studies on heredity, and, when they did so, only Darwin, Galton, and Nägeli were

mentioned. Thus, there is a major gap in the educational literature available to teachers

with respect to the treatment of scholars studying heredity in the second half of the 19th

century, who paved the way to the emergence of classical Genetics, into which Mendel’s

work, once reinterpreted, was embedded, even though he was not part of that community

of scientists working on heredity (Kampourakis 2013).

Does the availability of informed and critical articles about Mendel and his story

in journals means that teachers are well-supported in his classroom work on this topic?

Not so. A research-practice gap in general education (Kennedy 1997; McIntyre 2005;

Miretzky 2007) and, also, in science education (Pekarek et al.1996; El-Hani and Greca

2013) is generally recognized by educational researchers and teachers. That is, most

teachers do not apply research findings in their everyday classroom work and often do

not ascribe much value to the contribution of academic research to their own practices,

because of what they perceive as its lack of relevance (Kaestle 1993). Teachers are more

inclined, thus, to use other sources to build their pedagogical practices, such as popular

science magazines and internet sources.

These arguments suggest research avenues to be pursued in the future by the

HPST community: (i) to extend the analysis of how Mendel and his work are interpreted

to popular science magazines and internet sources; (ii) to enrich the discussion about

Mendel and his story, and, in particular, about the theories of heredity built and debated

in the 19th century in journals, popular science magazines, and websites; and (iii) to build

and investigate historically and philosophically-informed teaching sequences on Mendel

and classical Genetics to be used in the science classroom. If these avenues are pursued,

we may contribute to diminish the incidence of myths and misunderstandings about

Mendel’s work in school science as well as provide bases for a richer picture of the social

construction of knowledge about inheritance that culminated in classical Genetics.

32  

Evidently the idea is not that school teachers could solve problems still under discussion

in the historical literature. The point is, rather, that it is important to avoid treating

Mendel’s contributions as uncontroversial, overcoming the mythic Mendel that has been

dominating the discussion of his work in Genetics teaching. It is regrettable that the

treatment of Mendel is usually problematic in biological education, since it is often one

of a few instances in which history of science is considered in biology classrooms.

Acknowledgements I am indebted to the Brazilian National Council for Scientific and Technological

Development (CNPq) for a productivity research grant (no 301259/2010-0) and both CNPq and the

Research Support Foundation of the State of Bahia (FAPESB) for research funding (Project

PNX0016_2009). I would like to than two anonymous reviewers and Kostas Kampourakis for their

comments, which helped to significantly improve the paper.

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Table 1: Overview of articles for teachers addressing Mendel’s work.

Papers Goals of Mendel’s

work

Laws of segregation

and independent assortment

Hereditary particles

Reinterpretation of Mendel’s work

after rediscovery

Misconceptions about dominance

Reference to scientists studying

inheritance in the 19th century

Mendel in school science

Observations

Kritzky (1973, 1974)

Hybridization, but also blended

inheritance

Mendel developed

“Mendelian genetics”

Nägeli and Darwin.

Mendel inclined to believe in

evolution, but skeptical about

natural selection. Darwin not

aware of Mendel’s work

Hedtke (1974)

Darwin. Darwin knew

about and understood

Mendel’s work, but thought it

contradicted his theory

Corcos & Monaghan (1985)

As taught today, not

found in Mendel’s

writings

Idea not clearly

expressed in Mendel’s

works

Discussed in the paper, focusing on how subsequent reinterpretation is read back in his

work

Discussion of myth that Mendel thought that

dominance was always observed

Nägeli Criticism of textbook portrayal of

Mendel’s experiments without

historical perspective, only with later interpretation

40  

Table 1 (cont’d) 

Papers Goals of Mendel’s work

Laws of segregation

and independent assortment

Hereditary particles

Reinterpretation of Mendel’s work after rediscovery

Misconceptions about

dominance

Reference to scientists

studying inheritance in the 19th century

Mendel in school science

Observations

Jiménez Aleixandre & Fernández Pérez (1987)

Was Mendel really after a

theory of heredity, or is

this just anachronistic

reading?

Controversial if they are present in Mendel

Debates about developments

found in Mendel’s original work and

attributed to it after its

rediscovery

Nägeli How an extract of Mendel’s 1866

paper was used as primary source in

Genetics teaching at High School and

University, for, e.g., addressing aspects

of scientific methodology

Huckabee (1989)

Mendel interested in

showing, contra Darwin, that

variability results from parental

input, not from changes in the environment

Discuss influences on Mendel, addressing how

he was stimulated to engage in plant

hybridization, who were his precursors, and why

he succeeded where others had failed

Banet & Ayuso (1995)

Not found in Mendel’s writings

Mendel’s findings misinterpreted

due to posterior developments attributed to

original work

Critical appraisal for lack of historical

approach, despite central role of

Mendel’s laws in Genetics textbooks

Controversies about Mendel’s work

considered. Textbooks greatly responsible for

myths about Mendel and his work

41  

Table 1 (cont’d) 

Papers Goals of Mendel’s

work

Laws of segregation

and independent assortment

Hereditary particles

Reinterpretation of Mendel’s work after

rediscovery

Misconceptions about dominance

Reference to scientists studying

inheritance in the 19th century

Mendel in school science

Observations

Allchin (2000)

Mendel was after “law of

hybridization”

Discussion about its role as guide

for construction of classical Genetics and how we read back in it

our own conceptual structures

Main goal is to discuss these misconceptions.

Prevalence of dominance and

Mendelian genetics attributed to Mendel’s

authority

Critical appraisal of the tendency

to romanticize or idolize great scientists like

Mendel

Sigüenza Molina (2000)

The paper attributes posterior

developments to Mendel’s work,

repeating common problems in school

science

Students’ model about simple dominance, codominance, and

meiosis called “Mendel’s genetic

model”

Heppner (2001)

Mendel did not discuss

mechanisms of

inheritance

Mendel did not use the word ‘dominant’, or

derived concepts. The right translation would

be ‘predominant’, relating to character

distribution

Ayuso & Banet (2002)

Controversial if they are present in Mendel

Introducing Genetics with Mendel’s

examples can lead to overgeneralization of

dominance

Critical appraisal due

to lack of historical treatment

42  

Table 1 (cont’d) 

Papers Goals of Mendel’s

work

Laws of segregation

and independent assortment

Hereditary particles

Reinterpretation of Mendel’s work after rediscovery

Misconceptions about dominance

Reference to scientists studying

inheritance in the 19th century

Mendel in school science

Observations

Codina (2005)

Attributed to Mendel’s

work

Miyaki et al. (2006)

Attributed to Mendel’s

work

Emphasis on transmitted

hereditary factors that don’t mix in the hybrid plant.

Mendel’s notations A and a indicating

factors, not characters

Text about Mendel’s 1866 paper provided,

containing several statements

controversial in the historical literature

Melville & Fazio (2007)

Mendel proposed two transmitted ‘factors’ for each

trait, later confirmed as genes by T. H. Morgan

Mendel as example of individual who

proposed and supported with data

novel ideas, later verified by scientific

studies Madden (2007)

Mendel worked on inheritance in

plants and developed the idea

of particulate inheritance

Darwin faced difficulties resulting

from accepting blended inheritance.

Theory of pangenesis neglected

 

43  

 

Table 1 (cont’d) 

Papers Goals of Mendel’s

work

Laws of segregation

and independent assortment

Hereditary particles

Reinterpretation of Mendel’s work after rediscovery

Misconceptions about

dominance

Reference to scientists studying

inheritance in the 19th century

Mendel in school science

Observations

Colburn (2007)

Mendel’s explanation depended on

“factors”, later called “genes

Darwin’s theory challenged for lack of good explanation for inheritance of adaptations. Darwin’s contributions to

studies on heredity neglected

Unsupported claim that

challenges to Mendel’s work resulted from his appeal to

factors Texley (2008)

Darwin had rudimentary view of inheritance. Theory of

pangenesis neglected

Darwin described as botanist(!)

Caballero Armenta (2008)

A mechanism of inheritance was

present in Mendel’s work

Bizzo & El-Hani (2009)

Mendel’s findings explained in terms of the behavior of

traits. Idea of underlying factors

avoided

Darwin and Galton. Arguments for the fact that

Darwin was aware of Mendel’s work and obtained

similar results in his investigations. This did not

make him anticipate the evolutionary synthesis

Criticism of the curricular

proposal of teaching Genetics before Evolution,

as lacking historical or

cognitive support.

44  

Table 1 (cont’d) 

Papers Goals of Mendel’s

work

Laws of segregation and

independent assortment

Hereditary particles

Reinterpretation of Mendel’s work after rediscovery

Misconceptions about

dominance

Reference to scientists studying

inheritance in the 19th century

Mendel in school science

Observations

McBride et al. (2009)

Particulate inheritance attributed to

Mendel

Claim that Genetics resulted from Mendel’s work overstates

his contribution. Darwin’s theory of pangenesis neglected when stated that Darwin knew nothing of genetic inheritance

Passmore et al. (2009)

For Mendel, each individual has two

‘factors’ controlling each

trait

Students engaged in appraising

limitations of Mendel’s simple

dominance model

Jurkiewicz (2010)

Genetics described

as Mendel’s research

target

Mendel established link between Genetics and

Combinatorics, which changed the study of inheritance later, albeit not well

perceived in his times

Ferreira et al. (2010)

Attributed to Mendel’s work,

based on textbook (Pierce

2004)

45  

Table 1 (cont’d) 

Papers Goals of Mendel’s

work

Laws of segregation

and independent assortment

Hereditary particles

Reinterpretation of Mendel’s work after rediscovery

Misconceptions about

dominance

Reference to scientists studying

inheritance in the 19th century

Mendel in school science

Observations

Lorbieski et al. (2010)

Mendel proposed hereditary mechanism

Neglect of Mendel’s findings attributed to

lack of understanding of cellular structures and

cell division. This suggests that Mendel

understood inheritance at the cellular level

Offner (2011)

Attributed to Mendel’s

work

Anachronistic reading, referring

to “Mendel’s genes” and

characterizing his work as study on the “genetics of

garden peas”

Misconceptions about

dominance discussed

Mendel’s life and work could be used to

teach about NOS. Classical Genetics and

nature of the gene could be taught using

investigations on biochemical nature of genes associated with characters studied by

Mendel

Idea that Mendel was a lone genius put into

question. The monastery in Brünn was a center of

scientific learning

Bonner (2011)

Mendel interpreted his

results in terms of “invisible

mechanisms”

Misconceptions about

dominance found in this

paper

Concerns about introducing Genetics

using Mendel’s examples

Mendel share with current students

conclusion that Genetics has no role in evolution, given the misconception

that alleles are stable and cannot change

46  

Table 1 (cont’d) 

Papers Goals of Mendel’s

work

Laws of segregation

and independent assortment

Hereditary particles

Reinterpretation of Mendel’s work after rediscovery

Misconceptions about dominance

Reference to scientists studying

inheritance in the 19th century

Mendel in school science

Observations

Araújo et al. (2012)

Attributed to Mendel’s

work

Mendel claimed that plant

characters are due to

hereditary factors (now

known as genes)

Mingroni Netto (2012)

Mendel studied the transmission

of hereditary factors

Main goal is to discuss dominance and recessiveness

McComas (2012a,b)

Basic rules of

inheritance attributed to

Mendel

Extensive discussion of Darwin’s theory of pangenesis

and NOS lessons we can derive from it. Considers

Galton’s ideas about inheritance and how Mendel’s

work had no influence on Darwin