Gregor Mendel and the art of mis-communication

Aug 02 2012 Published by under Uncategorized

In this blog post I will expand the realm of my comments beyond phylogenetics, and consider verbal mis-communication in another part of biology.

Johann Mendel (he assumed the name Gregor upon becoming a religious novice) is famous within biology for two things: allegedly fudging his data, and being ignored until long after he was dead. I will discuss both of these things here, but it is the latter one that I particularly want to talk about today.

Much has been written about Mendel's work being ignored, with all sorts of reasons being proposed. Here, I want to point out something about Mendel's paper that is relevant to my theme of mis-communication in science, which I think contributed to its fate.

Many of you might also know that Mendel has been accused of adjusting some of his data to produce a "too perfect" result. I will return to this point in the next post.

Gregor Mendel may be one of the most famous biologists to have never made a direct contribution to biology. I say this because his published work in the field of genetics (of which he is considered to be the founder) was ignored until it was independently replicated 35 years later, separately by Carl Correns, Hugo de Vries and Erich von Tschermak (although much doubt has been cast on the role of the latter two people). So, if Mendel had never existed then the field of genetics today might be no different to what it is.

He published only one major scientific paper about what we now call Mendelain Genetics. (Most of his research work was on bee keeping and meteorology!) This paper reported the results of a series of plant cross-fertilization experiments involving varieties of garden peas (Pisum sativum). This was published in 1866 in Proceedings of the Natural History Society of Brno, where Mendel also published his meteorological work. It laid dormant there until 16 years after his death. This was in spite of the journal’s availability in the libraries of at least 115 institutions throughout Europe (although such journals were apparently not widely read at the time) and the availability and distribution of a series of 40 reprints.

We know that Mendel did much more work than this between 1856 (when he started the crossing experiments) and 1871 (he was appointed abbot of his monastery in 1868, and thus administrative duties came to occupy most of his time). Although his voluminous notes and manuscripts were burned (either late in his life or after his death), his correspondence with the botanist Carl Nägeli has survived (see Stern and Sherwood 1966 for an English translation). Mendel confirmed his pea results using at least twelve other plant species, although these results were never published, as well as trying inter-species crosses in beans (Phaseolus vulgaris), which are briefly mentioned in his published paper. He had considerable difficulties when examining species of hawkweeds (Hieracium), some of the results of which were reported in his only other (short) publication on hybrids (in 1870). Mendel made no other known attempts to publicize his work, either in writing or at scientific meetings.

Mendel’s work on cross-fertilization is known to have been cited in the published writings of other biologists only about a dozen times before 1900, at which time his main conclusions were independently reached by at least two other botanists working on different species. Hugo de Vries published his work through both the Academy of Sciences in Paris and the German Botanical Society, while Carl Correns published his through the German Botanical Society. These works became generally known almost immediately. However, both authors acknowledged that they had encountered Mendel’s publications after reaching their own conclusions (although some doubt has been cast on de Vries' claim), and so Mendel’s work then became more widely known, even if it didn’t have any direct effect at the time of its original publication.

The obvious question is this: why was the published work ignored? There are many possible answers. MacRoberts (1985) has suggested that Mendel's work was not so much neglected as unknown, while Weinstein (1977) has noted that reports of its existence were widely available, even if the paper was not consulted. Moreover, it's conclusions were important to some people, notably Charles Darwin. Darwin tried unsuccessfully to explain inheritance through his theory of pangenesis, and Mendel's ideas (if Darwin had known of them and accepted them) would have saved him the trouble.

The answer I discuss here is: Mendel mis-communicated with is readers by presenting his work in what was an unusual way for his time. My thesis is this: Mendel was obviously a Galilean while presenting himself as being a Baconian. To explain this statement, I need to give you a bit of background.

Historically, there are four types of experiments that can be recognized (their names have been suggested by Medawar 1979):

Aristotelian — these are contrived experiments intended to demonstrate the truth of an idea. The experiment is forced to fit the preconceived proposition, which usually comes from a particular philosophical view of the universe, and the data are adjusted to fit the theory if necessary (rather than the other way around). This type of experimental procedure was the most common one for most of the recorded history of science.

Baconian — these are natural experiments, where things are simply observed as they really are. The idea is to avoid prejudice and preconception and thus to see reality for what it actually is. Since we might spend a whole lifetime without ever witnessing the particular combination of events that would reveal the truth in any one instance, we are allowed to stretch our experience by manipulating the world in arbitrary ways, to see what happens. Most developments in biology have initially been via these natural-history type of experiments.

Galilean — these are experiments by ordeal, where the world is manipulated in such a way as to discriminate between competing views about how it functions. The idea is to explicitly recognize several alternative hypotheses about how the world operates, and then to deduce the consequences if each of these hypotheses was true. Since these hypotheses won’t all predict the same consequences, it should be possible to manipulate the world in such a way that some of their predictions can be refuted. This the modern type of experiment.

Kantian — these are thought experiments, which try to overcome the fact that the way we experience the world is patterned by our own sensory perceptions. The idea is to create alternative theoretical universes that do not fit our ordinary perceptions, and then to test whether they are consistent with the world as we actually experience it. Most developments in physics in the past century have initially been via these thought experiments, as are most modern computer simulations.

In the 1800s the most common version of science was the Baconian one, and this is how Mendel presented his work. He wrote: "The object of the experiment was to observe these variations in the case of each pair of differentiating characters, and to deduce the law according to which they appear in successive generations." In other words, he says he idid the experiments first, and only later worked out an explanation for the results. Observation comes first and understanding second.

However, Fisher (1936) pointed out that this claim is not compatible with what Mendel actually presented in his paper. Fisher carefully reconstructed Mendel's work from the descriptions given in the paper, and concluded that there can "be no doubt whatever that his report is to be taken entirely literally, and that his experiments were carried out in just the way and much in the order that they are recounted." However, this conclusion led Fisher to a contradiction, because the experiments actually make no sense unless: "Mendel had a good understanding of the factorial system, and the frequency ratios which constitute his laws of inheritance, before he carried out the experiments reported in his paper." In other words, understanding must have come first and observation second, with the observations intended to test whether the understanding was correct.

Fisher reached this conclusion based on two things: (i) Mendel left out information that seems to be essential in order to understand why he did things the way he did; and (ii) Mendel failed to present or analyze a lot of the data that he claimed to have, which he would have done if he was searching for an understanding of the data. That is, Mendel had already worked out his ideas, and did precisely what was needed to confirm them, neither more nor less. As Fisher noted, he could have done more with the data he had, but apparently saw no reason to do so.

The same garden today.

This has several consequences for Mendel's paper, all of which involve mis-communication, which is the idea that I am presenting in this blog post. Mendel mis-communicated because he failed to realize how other people would see his work. He failed to communicate in their "language", and say things in a way that allowed them to immediately understand just how different his work actually was from what had been done before.

First, the substance of Mendel's paper is a hypothesis test and yet it is presented  as a search for information. The content does not match the packaging. The packaging comes from the 19th century while the content comes from the 20th century. As such, the scientists of neither century were likely to make head or tail of it. One has to understand Mendelian genetics in order to appreciate the content, and yet the paper presents itself as being a search for Mendelian genetics!

Once you understand Mendelian genetics, it is easy to see why Mendel designed his experiments as he did, but not necessarily otherwise. This is how Correns and de Vries came across his work — they had already worked out Mendelian inheritance before reading Mendel's paper and thus understood it. For a modern audience, Mendel would need to write his paper with the theory first, and then everything would follow logically. As Fisher noted: "his experimental programme becomes intelligible as a carefully planned demonstration of his conclusions." In modern parlance, "conclusions" would be better expressed as "predictions", as far as experiments are concerned.

There is nothing especially unusual about Mendel's ideas. However, it did take a conceptual leap to put all of the components together. One has to accept that: inheritance is particulate; genetic material is structural and comes in pairs; and each parent contributes equally. This leads to segregation and independent assortment, which are the key components to Mendelian genetics (see Wikipedia). However, instead of presenting this idea and then testing it, Mendel's presented it as a deduction from his results. As such, it is not very convincing.

Second, Mendel leaves out information that would be considered essential for a hypothesis test. His choices of what to explain and what to leave unexplained, form a characteristic pattern throughout his paper; and they are rather idiosyncratic by modern standards.

For example, why did he choose Pisum sativum as his test species? This is important, because this is still considered to be one of the best species to work with for Mendelian genetics. There are many varieties of it available (Mendel used 22), so that it is possible to pick plants that differ only in one, two or three characters (as needed); and these characters are each controlled by only one gene, so that they segregate and assort independently. In addition, the plants are easy to cultivate and they grow quickly. So, how did Mendel realize that he had stumbled upon an ideal species for study? One obvious suggestion is that he had his idea first, and then looked for the right species to experiment upon.

It is noteworthy the types of things that Mendel explained in detail compared to those things he left unexplained. As another example, he gave a number of gardening details that are of practical but not theoretical importance, and yet he did not explain how or why he chose precisely the seven characters that he did (out of the 15 possibilities he listed in the paper), which surely is of great scientific importance (since each just happens to be controlled by one gene).

Third, Mendel called his work "hybridization" when it is really about heredity. This follows his predecessors' terminology, but it creates several sources of confusion. For example, Mendel was doing something completely new but he failed to point this out, by trying to phrase things as though they came from the past. Second, he confused the difference between inter- and intra-species variation. He said that this is merely a matter of degree, and the distinction does not matter; but it actually matters vitally for his work. In modern terms, Mendel was doing "experimental breeding" within a singe species, where the individuals are very similar to each other and inter-breed naturally. Other people were doing "hybridization of species", which differ in a large number of factors and do not normally inter-breed. Mendelian genetics is relatively easy to demonstrate within a species but not between species, and so Mendel's work was actually a significant advance over his predecessors.

Fourth, Mendel failed to distinguish alternative hypotheses that would explain his data, as would be required by a true Galilean experiment. In particular, blending inheritance could also produce his results, and this was the prevailing idea during his lifetime. Mendel contented himself with noting that, although hybrids tend to look intermediate between their parents overall, each individual character on its own is the same as one parent or the other. This is insufficient grounds for dismissing blending. Mendelian genetics predicts specific ratios of characters in the offspring of the crosses, such as 2:1, 3:1, 9:3:3:1 etc, depending on the circumstances. Blending inheritance does not predict any particular ratios at all. So, how does observing 2:1 or 3:1 support Mendel versus blending? These ratios are predicted by both hypotheses! Mendel failed to address this issue.

Mendel's argument here is that the proper way to arrive at a law governing hybrids is to investigate the behavior of specific characters of the hybrids, rather than considering the form of the plant as a whole. It was this decision to look at single characters of plant crosses that distinguishes Mendel's experiments from those of his predecessors. Blending inheritance looks at all characters simultaneously, rather than one character at a time. However, Mendel merely stated his new approach as an unquestioned assumption at the start of his paper. He couldn't really expect to get away with this! If you are going to dismiss as irrelevant the work of all of your predecessors, you had better have a very strong argument. Otherwise, they have no good reason to accept your conclusions over their own.

Fifth, Mendel failed to cite important predecessors. Most importantly, he never referred to Carl Nägeli, and Nägeli never cited Mendel in his own work. However, Mendel did recognize Nägeli as an important scientist in his field, since they corresponded by mail. It is therefore ironic that the only clues we have to Mendel's thoughts about his work are from the letters that he wrote to Nägeli, as all of Mendel's own papers (including Nägeli's replies to Mendel) were destroyed.

Finally, Mendel did not present himself as much concerned about demonstrating the precision or consistency of his results. He presented data that confirm the ratios that he was expecting and then stopped. Moreover, his arguments were entirely statistical. He never observed exactly the ratios that he claimed (eg. a ratio of 2.9:1 was called 3:1), which we interpret as due to random variation. However, this only works if you are already expecting 3:1. If you have no prior expectation, then how can you know that the difference between 2.9 and 3.0 is random variation rather than vitally important? Mendel, however, never addressed this question.

Also, he repeatedly referred to data that he had but did not present (Fairbanks and Rytting 2001 list much of the work Mendel did to collect the unpublished data), and these data could easily have be used to further investigate Mendelian inheritance. So why did he not analyze them? If he was searching for patterns in his data, as he claimed, this seems remiss. He didn't even bother to test his two basic ideas: that both parents contribute equally to inheritance, and that characters are inherited independently. And yet he had data that would test these! Mendel treated these as unquestioned assumptions, rather than as deductions from his work. This is not the behavior of a Baconian, as Mendel claimed to be.

So, Mendel's work was done as though it was part of the early 20th century but was presented as though it was part of the early 19th century. It was thus a strange hybrid that didn't fit easily with the practitioners of either group. If Mendel was writing for a modern audience then he needed to explain more of his background knowledge; and if he was writing for an earlier audience then he should have done more with his data. He was ahead of his time while trying to be a part of his time, and it didn't really work out for him.

References

R.A. Fisher (1936) Has Mendel's work been rediscovered? Annals of Science 1: 115-137.

Michael H. MacRoberts (1985) Was Mendel's paper on Pisum neglected or unknown? Annals of Science 42: 339-345.

Peter B. Medawar (1979) Advice to a Young Scientist. Harper & Row, New York.

Gregor Mendel (1866) Versuche über Pflanzen-Hybriden. Verhandlungen des Naturforschenden Vereines im Brünn 4: 3–47.

Gregor Mendel (1870) Ueber einige aus künstlichen Befruchtung gewonnen Hieracium-Bastarde. Verhandlungen des Naturforschenden Vereines im Brünn 8: 26–31.

Curt Stern, Eva R. Sherwood (eds) (1966) The Origin of Genetics: a Mendel Source Book. W.H. Freeman, San Francisco.

Alexander Weinstein (1977) How unknown was Mendel's paper? Journal of the History of Biology 10: 341-364.

 

6 responses so far

  • Jim Thomerson says:

    Interesting! If you go to Brno, there is now a Mendel Museum in the Abbey of St Thomas. Mendel was an accomplished plantsman. One of the portraits of him shows him holding a flower from one of his fuchsia hybrids. Am I correct in thinking hawkweed has a pair of ring chromosomes, and therefore would not show independent assortment? If he had worked on bees, as he planned to do, he would have been completely confused by the haploid diploid inheritance system. Mendel's work was before there was much development of statistics. He knew he had to have lots of numbers, but quit when they suited them. Today one would design an experiment to obtain the requisite numbers to show a particular level of difference as adequately significant.

    I understand there is a copy of Mendel's paper in Darwin's library, but the pages are uncut. It has been argued that Darwin was thinking of much more subtle variations and would not have understood the importance of Mendel's work. I understand Mendel had annotated his copy of the Origin, and have the idea he was not much impressed.

    In teaching genetics, I went from treating Mendel first, to looking at the results of his three, as I call them, midwives. Here there are situations without complete dominance; the heterozygote is distinctive, and the arguments are much easier presented.

    Tschermak lived until 1962. It is amazing to think that his career ranged from discovering Mendel, to, probably, reading of the decoding of the genetic code, which started in 1961.

    • Jim, Thanks for your interesting (and informative) comments. Hawkweeds have a type of parthenogenetic (asexual) reproduction, technically called gametophytic apomixis. In the pictures I have seen the chromosomes look normal, although they are mostly tri- and tetraploids. Since Mendel's work refers specifically to sexual reproduction, it would not apply to most hawkweeds. Mendel's statistics are discussed in my next blog post. Darwin's supposed copy of Mendel's paper is discussed on this web page. Mendel's opinion on Darwin's work is the subject of much discussion by historians (including Fisher in his 1936 paper), without much resolution, given how little documentation there is. Darwin might have grasped Mendel's work, as his way of working was rather similar to Mendel's, but he would first have had to accept Mendel's assumptions. /David

  • [...] principles and gone further ahead in his work on evolution anyway; there are suggestions that Mendel’s writing style was too archaic for practitioners of his day to read and adopt it! (So, it is not merely lack of good reference [...]

  • Yoselie says:

    Hola, soy estudiante del profesorado de Biología. En el curso surgió la discusión sobre que tipo de investigación realizó Mendel. Gracias a este artículo, tengo varias herramientas para comprender y seguir el debate sobre Mendel.
    Muchas gracias!!!!!

  • help me!!!!!!!!!!!!!!!!!!!!!!!!! what was his most famous publication