Historian's demythologizing acid

reviewed by Gert Korthof   24 Aug 2003   (updated 15 Oct 2005)

Mendel never grasped the basic tenets of Mendelian genetics (9), Darwin was a Lamarckist throughout his life and Pasteur suppressed unwelcome data. – This is the disturbing message of John Waller's Fabulous Science. We know that scientists rewrite the history of their discipline and create myths around the founding fathers of their disciplines. But Waller's demythologizing acid so aggressively corrodes the myths of our scientific heroes and revolutions, that one cannot help wondering whether any heroes or revolutions survive his treatment at all.

Pasteur: right for wrong reasons

Mendel did not understand Mendelian Genetics!

The result of the fertilisation may be made clear by putting 
the signs for the conjoined egg and pollen cells in the form
of fractions, those for the pollen cells above and those for
the egg cells below the line. We then have 

	  A	  A	  a       a
        ----- + ----- + ----- + -----
	  A	  a	  A       a

"We may write then A/A + A/a + a/A + a/a = A + 2 Aa + a."

Microscopes and chromosomes

   Waller claims "it would be most unreasonable to suppose that he [Mendel] could have done so. The idea of allelic pairs only began to make real sense around 1900 - when scientists had good enough microscopes to detect the existence of chromosomes". The good thing here is that Waller connects Mendelism and chromosomes (16), but there are two reasons why I think Waller's claim is wrong. The first is the timing and the ambiguous nature of the cytological evidence. The second reason is the logic of the Mendelian ratios.
Waller is imprecise in the timing. Crucially, at the time of the rediscovery, 1900, it was not accepted that chromosomes exist in pairs, that they pair and then separate in the formation of germ cells. It was not until 1903, three years after the rediscovery, that W.S. Sutton gave the first modern interpretation of the relationship between genes and chromosomes (7). This is further confirmed by Portugal and Cohen: "Within a few years after the verification of Mendel's work, the relationship between the chromosome (but not DNA) and Mendelian genetics was established" (8). But even this knowledge is not enough to explain the Mendelian ratios. Historian Jan Sapp points out (discussing meiosis) that "a crucial idea was lacking: cytologists had not yet generally agreed on chromosomal individuality - the notion that different chromosomes had different properties. In 1883 Wilhelm Roux postulated that each chromosome carried different hereditary determinants. But the experimental evidence was not reported until 1902 [ after the rediscovery! ], when Theodor Boveri announced that each of the 36 chromosomes of the sea urchin were necessary for normal development." (15).
   Despite Sutton, there had been much reluctance among geneticists to accept the chromosomal theory of heredity. William Bateson (1861-1926), the father of the word 'genetics', the founder of the Journal of Genetics and one of those who reproduced Mendel's results, never accepted the chromosomal account of inheritance! Therefore, the connection between chromosomes and Mendelian genes, is certainly not self-evident (19,20).

   Furthermore, pre-1900 cytological knowledge about mitosis and meiosis would not have helped the rediscoverers very much (17). The relation between Mendelian factors and chromosomes is not so simple. How could a varying number of stainable threadlike particles of different lengths and forms, which were called 'chromo-somes' (stained bodies), be identified as the carriers of heredity? We should certainly not make the mistake to associate chromosomes with DNA, because this powerful association only developed decades after the rediscovery of Mendel. Furthermore, why should animal chromosomes behave in the same way as plant chromosomes? Why could it not be a coincidence that chromosomes come in pairs and Mendelian factors come in pairs too? Illustrative of the incomplete knowledge of the time is that August Weismann [before 1900] envisaged that each of the many chromosomes present in the cell nucleus carries all of the hereditary units necessary for producing the entire individual. In Pisum sativum, whose nuclei contain 14 chromosomes, this theory was clearly incompatible with Mendel's (then still unknown) inference that the pea plant is endowed with two, rather than fourteen, copies of each of its hereditary units (11). For humans it would mean that there are 46 copies of each gene. Weismann's theory is opposed to the whole idea of diploidy and the idea that each gene is present in pairs. Therefore, it is clearly not enough to know that sperm and egg contribute the same number of chromosomes, that chromosomes come in pairs, and that those pairs pair and segregate during meiosis. One needs to know that each chromosome pair is unique and contains only one pair of a specific gene. It is crucial to know how many copies genes have and how they are distributed over chromosomes. One cannot see that through a microscope.

the logic of the ratios

    The second reason why I disagree with Waller's claim that it would be most unreasonable to suppose that Mendel could have inferred the idea of allelic pairs, is the logic of the Mendelian ratios. The 3:1 ratio logically requires that the hereditary factors exists in pairs! (at least for heterozygotes). The assumptions are:

1. hybrid parents produce 2 different gametes with only one factor per gamete
2. the 2 types of gametes are produced in equal proportions
3. this gives 4 possible equally likely combinations of the gametes

not relevant

   Furthermore, the fact that Mendel wrote homozygotes as A instead of AA has no effect at all on the 3:1 ratio. This is because a homozygote (a 'pure' plant) produces only one type of gamete (by definition). An identical pair still produces one type of gamete. From our present-day perspective, a homozygote is diploid, has a pair of identical alleles, and so Mendel used a 'wrong' notation, but in the context of the ratios this does not make a difference. The crucial assumption here is that the hybrid has a pair of factors. Of course Mendel could not miss that, because A and a are a pair. Therefore, Waller is imprecise in claiming that it is unreasonable that Mendel could not have inferred a pair. Mendel could not prove that homozygotes have a pair. However, he did not need such a proof. And this is not because he could not see chromosomes, but because it was not necessary to explain his 3:1 ratio. And because he did not need it, it was no hindrance for the full explanation of the ratio. According to geneticist C. D. Darlington, Mendel evaded the unproved doubleness of the homozygotes. Mendel's successors made the next step and described the homozygotes as AA. "A step Mendel himself would no doubt have made had he ever met a single person with whom he could seriously discuss his ideas" (14). It seems that Darlington was the only geneticist who correctly read Mendel's paper (independently of Olby).

no explanation? only descriptive?

I strongly disagree that Mendel's work was 'purely a descriptive exercise'. Mendel's statement "The internal composition of the egg and pollen cells of hybrids" is beyond pure description. One cannot see the 'internal composition' of eggs. It is an inference. Of course Mendel did not believe that green or yellow colours were somehow present in seed. Mendel certainly tried to explain his observed ratios by a hypothetical unobservable internal composition of egg and pollen. Of course he could not see the presence of the recessive factor in a hybrid with a dominant phenotype. It is also an inference. Waller does not mention Mendel's manipulation of data (2) (a lost opportunity!). If Mendel had no expectations about 'correct' ratios, how could he or his assistant consciously or unconsciously 'correct' his data?

If one concludes, as I do, that the cytological evidence in 1900 was too incomplete to support allelic pairs and that the logic of the ratios alone should be enough to infer allelic pairs for both homozygotes and heterozygotes, the question arises: what exactly did the rediscoverers rediscover? Only Mendel's ratios or the correct interpretation too? It is perfectly possible that they only reproduced the Mendelian ratios in 1900. One needs to investigate how they described their homozygotes. Did they write AA in 1900 or was it a few years later when cytological evidence became convincing enough?

historical lessons

I agree with Waller that geneticists after the rediscovery of Mendel have interpreted Mendel with the benefit of hindsight and in doing so obscured Mendel's struggle with the correct interpretation of his data (13). We now have a more realistic view of Mendel's achievement. But more importantly, instead of undermining the genius of Mendel, historical research gives us insights in the intellectual struggle of those who made scientific revolutions. We gain insight in how scientific discoveries are made. If anybody is to blame it is not Mendel but those who misinterpreted him. On the other hand, if historical accuracy is sacrified for the sake of efficient training in genetics, then this seems harmless efficiency. A general conclusion is that revolutionary ideas never come fully formed. Even when we view an ingredient (allelic pairs) of a conceptual system (Mendelian genetics) as logically necessary today, it is possible that it is not present in the theory of the inventor. Maurice Wilkins, the third man of the double helix, reported in his autobiography (21) that Chargaff, who discovered that both C:G and A:T ratios were always 1:1, amazingly never inferred base pairing from his ratios. With hindsight it is obvious that base paring explains the 1:1 ratios. The DNA bases C and G form C-G pairs, and A and T bases form A-T pairs. But for Chargaff it was not obvious at all.

Genetics: paradigm of successful science

   It is beyond Waller's scope that the development of genetics as a science is the prime example of progress in biology. The development of the concept of the gene from an abstract speculative entity to a physical object that can be manipulated in a test-tube, is a paradigm of successful science. Even in the flourishing period of classical Mendelian genetics, 1900 - 1950, the gene was an abstract theoretical entity. The physical basis of the gene was established by the landmark paper of Watson & Crick in 1953.

Darwin: a lifelong Lamarckist

Typically, the chapter about Charles Darwin is called "The origin of species by means of use-inheritance". A subtle hint to Darwin's lifelong Lamarckism!

Waller attacks four Darwinian myths:

1. myth 1: Darwin's theory of evolution was original and a complete break with the past.
   According to Waller "Historians now recognise that the core principles of evolution – struggle for survival, selection, heritability, adaptation, even the appearance of random changes to the hereditary makeup – were fairly common themes in Victorian botany and zoology." I have no problem in searching for historical forerunners of Darwin, and pointing out misconceptions, but the result seems to be that the Darwinian revolution becomes a mystery. If every ingredient of evolution was there, what did Darwin do? Only piece the parts together? Was there a revolution at all? If every part of the theory was known, why was there strong opposition to Darwin's theory? It looks as if Waller's main goal is to destroy all the originality of Darwin. One could as well claim that Shakespeare was not very original because he only arranged existing words in a particular order.
2. myth 2: The great achievement of Darwin was that he replaced Lamarckian inheritance of acquired characteristics with random variations and natural selection.
   Waller claims that Darwin believed in Lamarckian inheritance of acquired characteristics during all the subsequent editions of the Origin. However, even the historian of science Peter Bowler has a more balanced view: "Darwin himself accepted that the inheritance of acquired characters might supplement natural selection and his view of heredity allowed for the effect to occur" (5, p. 236). According to Strickberger "at times Darwin accepted the Lamarckian view of the inheritance of use and disuse" (22).
3. myth 3: Darwin treated the causes of variation as a black box because he had no good theory of heredity.
   According to Waller, Pangenesis was very good science! Darwin 'knew' how new genetic variation was produced, it was not a black box for him. A non-blending theory of inheritance was readily available to Darwin. His cousin Francis Galton developed an ingenious particulate theory of heredity.
4. myth 4: Darwin consistently claimed that evolution is not progressive.
   Waller claims that Darwin believed in progressive evolution, but he does not give good evidence for his claim.

Huxley and others

   Waller has done great service to busy readers interested in the scientific method, scientific controversies, and the history of science by summarising many books and articles in the recent history of science. The result is an introduction to a diversity of issues from a diversity of disciplines one would otherwise not have encountered.
Waller's claim that Mendel did and could not understand Mendelian genetics is wrong. Mendel's explanation for the ratio's is correct despite his puzzling notation and despite his lack of cytological knowledge. It seems that Waller himself failed to understand the full force of the logic of the Mendelian ratio's. Contrary to what Waller seems to think, the historical context Mendel's experiments does not affect the logic of the ratio's.

Notes

1. John Galloway: Airbrushing science. Nature 422, 19-20 (2003) 6 March 2003. (is a review of the book).
2. R. A. FISHER Has Mendel's Work Been Rediscovered?, From Annals of Science, 1 (1936).
3. Richard Dawkins(2003) A Devil's Chaplain. Selected Essays by Richard Dawkins, p.68.
4. Ernst Mayr(1982) The Growth of Biological Thought, p.720,721
5. Peter Bowler(2003) The history of an idea, third edition, p.262.
6. On page 281 White's work is "History of the Conflict Between Science and Religion"; and on page 282,283 it is "Warfare of Science with Theology". According to Arthur Strahler the work was first published in 1896 and reprinted in 1978. Another reference is: Arnold D White(1898) "History of the warfare of Science and with Theology in Christendom".
7. Srb, Owen, Edgar (1965) General Genetics, p.34
8. Franklin Portugal and Jack Cohen (1977) "A Century of DNA. A History of the Discovery of the Structure and Function of the Genetic Substance", p. 115 (emphasis is mine).
9. Recently, James Gleick added Newton to this hero-debunking list: "Newton of all people was no Newtonian". Patricia Fara (2003) "Was Newton a Newtonian?", Science 301 (5635), p.920, 15 Aug 2003.
10. Even more amazing, Enrico Coen mentions in his splendid The Art of Genes (244-245) that Darwin did crossings with Antirrhinum and reported a ratio of 37 : 127 (1 : 3,4)! Darwin completely missed the importance of this result!
11. Gunther Stent and Richard Calendar(1978) Molecular Genetics. An Introductory Narrative. Second Edition, p.12.
12. Rusiko Bourtchouladze (2003) "Memories are made of this. The Biological Building Blocks of Memory", Phoenix paperback, p. 15. (well written book, agreeable reading)
13. An example is Brian Silver's description of Mendel's discoveries in his The Ascent of Science (p.262). After an introductory paragraph about Mendel, he asks "What would we expect from these experiments?", thereby completely sidestepping what Mendel wrote! How can one ever discover how scientific discovery works and how scientific revolutions are made? Compare also with Sturtevant below.
14. C.D. Darlington (1966) "Genetics and Man", Penguin Books, p.98.
15. Jan Sapp (2003) "Genesis. The Evolution of Biology", p.89.
16. Jan Sapp does not discuss the possible relation of chromosomes and Mendelian factors at all, although he is interested in cytology. He does not mention the AA or A problem.
17. With the benefit of hindsight the discovery of salivary gland chromosomes showing clear banded strands by Balbiani in 1881 seems highly informative, but they were wrongly interpreted at the time (see Sturtevant book below, page 75).
18. Alison Abbott (2003) Neuroscience: Genomics on the brain, Nature 426, 757 (18 Dec 2003).
19. Stephen Jay Gould (2002) "The Structure of Evolutionary Theory", p.410
20. A.H. Sturtevant (2001) "A History of Genetics", page 49.
21. Maurice Wilkins (2003) "The Third Man of The Double Helix", Oxford University Press, pp.226-227.
22. William Hamilton wrote "Lamarck's idea of a mechanism was plausible, so plausible indeed that Darwin, as he grew older, under the pressure from physicists telling him that his time was too long and of engineers telling him his heredity was unworkable, became more of a Lamarckist, less of a selectionist" (Narrow Roads of Gene Land, Vol 3, page 223). This means that Darwin's Lamarckism was not a constant factor, but one that increased during his lifetime. [Note added 10 Aug 2011]

Further Reading

• Email from John Waller.
• Waller's home page at the Dept of History and Philosophy of Science of the University of Melbourne, Australia.
• Mendel, Mendelism and Genetics by Robert C. Olby (full text available on the MendelWeb site). In section 3 "Mendel as Founder" Olby points out the absence of double letters to represent the pure breeding individuals. This is the most important fact on which Waller bases his argument. There is also an important paragraph "Mendel and the Darwinians" in which Olby discusses Mendel's ideas about evolution and how Darwinists initially reacted to Mendel. The Mendelweb also contains Mendel's paper.
• A.H. Sturtevant(2001) A History of Genetics. A paperback reprint of the 1965,1967 edition. The full text of the book is available on-line at the Electronic Scholarly Publishing site, in PDF format. Additionally Mendel's original paper and many other classics in genetics are available. Sturtevant confirms Stent and Calendar's observation that Weismann concluded that each chromosome carries all the hereditary elements necessary to produce a whole individual (p. 19). I could not have imagined this possibility! With our current genetic knowledge it is unthinkable that each chromosome contains the information for a whole individual. For humans it would mean that each gene has 46 copies. This theory clearly contradicts the idea that each genetic character comes in pairs. There is one remarkable fact about Sturtevant's book: he did not discuss Mendel's paper! How could he have noticed Mendel's inconsistent interpretation when he did not read Mendel's paper carefully? It seems Sturtevant is just not interested in how Mendel himself interpreted his results.
• Deviations from Mendel's laws (non-Mendelian inheritance) are discussed in Mark Ridley Mendel's Demon. Gene Justice and the Complexity of Life and Gabriel Dover Dear Mr Darwin. Letters on the evolution of life and human nature on this site.
• Rescue science's history from historians! Pasteur knocked off pedestal? (Nature, free access)
• DNA timeline with cartoons and starting with Mendel...
• Jan Sapp (2003) Genesis. The evolution of Biology. In other respects this is an interesting history of biology. Sapp discusses non-Darwinian and non-Mendelian mechanisms usually omitted in history of biology textbooks.
• John Waller (2003) Einstein's Luck: The Truth Behind Some of the Greatest Scientific Discoveries (the USA edition of Fabulous Science). Reviewed in American Scientist online issue: January-February 2004.
• John Waller (2003) The Discovery of the Germ. Twenty Years That Transformed the Way We Think About Disease. Columbia University Press, New York, 2003 Hardback: 205 pp., illus.
• Elof Axel Carlson (2004) Mendel's Legacy: The Origin of Classical Genetics. Cold Spring Harbor Laboratory Press. Previous histories of classical genetics have highlighted the successes and neglected the failures says geneticist and historian of science E. A. Carlson. There is an enthousiastic review of the book by Garland Allen 'Peas and helices' in Nature 430, 404 22 July 2004
• John Waller (2004) Leaps in the Dark, Oxford University Press.
  • Review in the NewScientist.com (Dec 2004):
    "DO YOU think James Lind proved that fruit juice prevents scurvy? That Robert Watson-Watt invented radar? That Isaac Newton showed a prism splitting white light into pure colours? Reader, you are the weakest link in the history-of-science round and must leave the contest. If only you had read John Waller's Leaps in the Dark, you would have known better. Like his earlier successful book, Fabulous Science, it examines a collection of hoary tales from science's past. All their tellers are convicted of crimes ranging from oversimplification to outright falsehood. Sometimes, as with Watson-Watt or the microbiologist Selman Waksman, credited with discovery of streptomycin, this is due to mere self-promotion. Other cases are due to myth-making attending the foundation of new professions such as psychiatry. Most often though, they are due to romantic notions of heroic enlightenment beating back the forces of reaction." 01-01-2005
  • review by Walter Gratzer "Feet of clay. There's more to science than doing the research". Nature, 433, 10 Feb 2005. 10-02-2005
• Peter J. Bowler and Iwan Rhys Morus (2005) Making Modern Science. A historical Survey. Reviewed in Science 30 Sep 2005.
• Jeffrey Crelinsten (2006) Einstein's Jury: The Race to Test Relativity (Hardcover) "Crelinsten presents the surprising fact that virtually all astronomers engaged in crafting the empirical tests of relativity for a period of almost two decades had very little understanding of the theoretical physics and mathematics underlying Einstein's principles. Nonetheless, astronomers from around the world spent years chasing solar eclipses in an attempt to gather data, and each held strong opinions about whether or not Einstein's theory was correct. Crelinsten is best when discussing the attacks on Einstein and his theory, demonstrating that some arose from ignorance, some from petty jealousy and some from anti-Semitism." GK: Interesting and important: first compare what C. tells about the first supposed confirmations of Einstein's theory with what Waller says, second because similarities with attacks on Darwin's theory.
• A review of Vitezslav Orel (1996) Gregor Mendel, the First Geneticist (Oxford University Press) by Gerdien de Jong, J. evol. biol. 11 (1998) 265-268.
  "Mendel denoted such a result as a simple series A + 2Aa + a." "The Versuche über Pflanzen-Hybriden present all three 'Laws of Mendel', and the idea that traits are coded for by Anlage, self-contained units present in duplicate, of which one is given to the offspring by each parent."
  GK: This review was published before Waller (2002). The expression A + 2Aa + a cannot be 'phenotypes', because A and Aa cannot be distinguished, so it must be 'genotypes'. But A and a are obviously not duplicate! So, according to Mendel homozygotes do not have duplicate Anlagen. Only heterozygotes have duplicate Anlagen. This contradiction is not noticed in the review. Interestingly, the reviewer also notes: "By 1860 it was not yet certain that one male cell fertilized the female cell."; "Between 1865 and 1900, major changes occurred in the thinking of naturalists. The sufficiency of one spermatozoon for fertilization was established." Could Mendel not have inferred from his 3:1 ratio that 1 spermatozoon was involved in fertilization? 26 Sep 2006
• Jim Endersby (2007) reviews: Morse Peckham (editor), CHARLES DARWIN'S ORIGIN OF SPECIES (Variorum Text) University of Pennsylvania Press. and Frederick Burkhardt and Duncan Porter, (editors) THE CORRESPONDENCE OF CHARLES DARWIN.
  A very useful review of Darwin myths and how historians correct them 2 May 2007
• From a review of Theodor Boveri 'Concerning the Origin of Malignant Tumours':
  "Boveri is remembered for the seminal idea, laid out in Concerning the Origin of Malignant Tumours, that chromosomes are the seats of cell heredity, and that the atypical chromosomes often seen in cancer cells are the basis of these cells' aberrant behaviour. In truth, much of the credit for this prescient suggestion should go to the pathologist David von Hansemann, who, beginning in 1890, published a series of papers on the subject. Von Hansemann noted the tight association between abnormal numbers of chromosomes (aneuploidy) and malignant tissues (neoplasias), but he did not conclude that one invariably causes the other. Boveri notes von Hansemann's contribution in passing and presents evidence for just that conclusion." [ 10 Jun 2008 ]
• Héloïse D. Dufour & Sean B. Carroll (2013) History: Great myths die hard, Nature, 3 Oct 2013.
• Hiram Caton (2007) Getting Our History Right: Six Errors about Darwin and His Influence, Evolutionary Psychology 2007. 5(1): 52-69
  • Caton debunks 6 myths about Darwin. (pdf is free) Caton is very critical of the impact of Darwin on science (biology), theology and society. The article seems to be written in a hurry and with an anti-Darwin bias, but contains interesting references. Caton is not a biologist. Part of his assertions are correct, but not always relevant, and part are incorrect. The American Museum of Natural History Darwin exhibition (2005-2006) can be found here. If Caton is right, creationists should not attack Darwin, but Louis-Constant Prévost, Louis-Melchior Patrin, Jean-Baptiste Lamarck, Julien-Joseph Virey, Jean-Baptiste-Julien d'Omalius d'Halloy, Bory de Saint-Vincent, Ducrotoy de Blainville, Etienne Geoffroy Saint-Hilaire, Ernst Haeckel, Patrick Matthew, Edward Blyth, Robert Chambers, Herbert Spencer, Lord Kelvin, Louis Pasteur, Joseph Banks, Adam Smith, Thomas Hobbes, John Locke, David Hume, George Combe, J.S. Mill, Baron d'Holbach, Auguste Comte, David Friedrich Strauss, etc.
    Why would Samuel Butler attack Darwin in stead of all the others mentioned above? etc.