by Douglas Allchin
It seems patently absurd to ask, "was Mendel a Mendelian?" Yet within this question lies fascinating clues about the origins of modern genetics, the philosophical and sociological nature of a discovery, and--equally important--its acceptance by the general community.
Most of us take Mendel to be the "father of modern genetics," but the case is far from clear. (At the outset, one may wonder what even a modest feminist might say about the image of patriarchy in science.) For example, we do not know exactly what problem Mendel was actually pursuing, but it was almost surely not the nature of hereditary factors or of the transmission of traits. He may have been looking at fertilization (whether one pollen cell fertilizes one egg each), or he may possibly have been trying to produce a true-breeding hybrid species: both were contemporary problems in agricultural breeding. Each also explains his attention to 3:1 ratios in offspring.
Second, Mendel worked at the level of observable characters and did not distinguish between traits and material units of heredity. Nor did Mendel see his `elements' (today's genes) as occurring in pairs in each organism. Mendel's notation clearly shows, as Robert Olby (1985) has noted, that an A x A cross yielded A + 2Aa + a: the homozygous form was `A'--not a diploid `AA'. That is, Mendel distinguished only weakly (as we are often at pains to do more strongly with students) between phenotype and paired alleles of the genotype. (Nor did Mendel use Punnett squares!--introduced in 1911 by Reginald Crundell Punnett at Cambridge).
Third, Mendel did not explicitly formulate "Mendel's 2nd Law," the principle of independent assortment. Though he did perform dihybrid crosses and reported 9:3:3:1 results, there was no formal recognition of the "independent" behavior of the two character states. In fact, the principles of segregation and independent assortment were not distinguished until much later (around 1905-1910) and were formally articulated by Thomas Hunt Morgan. Not until early geneticists encountered anomalous ratios in dihybrid crosses did they see the need to formulate a separate rule for "normal" assortment behavior. Bateson, for example, found a 12:1:1:3 ratio in sweet peas for flower color and pollen shape--a "violation" of assortment, but with segregation maintained.
Finally, in a lesser known paper in 1869, Mendel tried to generalize his results to another species, Hieracium. But the results were not the same. Mendel did not adhere to "his" principle that traits in hybrids segregate in producing further offspring. Quite to the contrary, he claimed that they remained constant (lending support to the historical notion that his goal was to produce true-breeding hybrids).
Was Mendel a `Mendelian', as we understand the term and as texts present it today? Possibly not! `Mendelism' may more accurately apply to a retrospective and complete theory of the gene as it was published by Morgan in 1926. What, then, was Mendel's role?
We know that Mendel's work gained prominence 35 years later, at the turn of the century. Why, and why not until then? Here, one can find important lessons about the transmission and development of ideas in science. Students may be reminded that a "discovery" is almost worthless unless someone else knows about it--and follows up on it. "Persuasion of peers," as John Jungck calls it, is an integral part of science, just as much as problem-posing and problem-solving. Further, as philosopher David Hull (1988) stresses, it is not just a matter of proving that you are "right": you have to convince fellow scientists to use and extend your findings; you must persuade them of the concrete worth or value of your discovery. Mendel published his results, but he was apparently not very successful in convincing others that his studies were useful--at least in the way we do today.
The story may not be quite so simple, though. Mendel is often portrayed as a recluse, whose published work in 1865 was sorely underappreciated. As Lindley Darden has commented, however, "a treasure hunt found numerous copies of, and citations to, Mendel's 1865 paper" (1991, p. 44)--and the historians' search has by no means ended yet. Three scientists (re?)introduced Mendel's paper in 1900: if it was indeed obscure, it was not so obscure that each managed to find it. But what did the "rediscoverers" see that others had not?
There is quite some historical controversy even about these "rediscoverers." Erich Tschermak, in Austria, referred to Mendel's 3:1 ratios, but did not link them to segregation of genetic factors: it is not clear from the context of his discussion that he appreciated Mendel's explanations in the sense that we do. Karl Correns, in Germany, had done his own research confirming the 3:1 ratios--but we do not know whether he began his work before or after finding Mendel's paper. Hugo de Vries, in the Netherlands, had been working for several years with the notion of unit-characters, akin to Darwin's pangens. He saw characters as linked to both development and the origin of new species. His work on the hybridization and recombination of unit-characters drew his attention, so he tells us, to the 3:1 ratios. But again, historians are not convinced of his own testimony and suspect that Mendel's paper may have prompted his experiments.
Gunther Stent (1972) has called a discovery `premature' if it cannot be connected by a series of logical transformations to the canonical or standard knowledge of the time. In this sense, Mendel's work may have been premature, or "ahead of its time." But his work may also have undergone a transformation of meaning in the years before its "rediscovery." That is, the canonical knowledge may have changed, and Mendel's work may not have been the same 35 years later.
So, if Mendel did not discover Mendel's laws, who did? We may conclude that the discovery was distributed among many people--making the historical tale more complex, but also much more interesting. In the years between 1865 and 1900, for instance, several developments made Mendel's patterns easier to appreciate. Issues of heredity, embryological development and evolution overlapped--since all addressed the origin or emergence of form, so there was a convergence of interests. Cell structure and fertilization had been actively studied, giving a sharper image of the cellular aspects of inheritance. Chromosomes would be seen as carrying the genetic material in 1905 and Sutton and Boveri would note how their behavior correlated with Mendel's `elements'. Each of Mendel's "rediscoverers," as well as the community in the early 1900s which adopted Mendel's work as a model, may well have been able to read more into Mendel than perhaps Mendel wrote.
By updating our image of Mendel, we may well lose a long-sung "hero" of science. But in doing so, we also gain a far more textured image of how science really happens.
Further Reading