Ronald A. Fisher - Should Mendel Be Taken Literally? lyrics

2. SHOULD MENDEL BE TAKEN LITERALLY? Bateson raised a point of great interest as to the conduct of Mendel's experiments in a footnote to a pa**age in the translation he used. After describing his first seven experiments Mendel opens his eighth (unnumbered) section with the words (p. 332) : "In the experiments described above plants were used which differedonly in one essential character" (wesentliches Merkmal). Bateson notes: "This statement of Mendel's in the light of present knowledge is open to some misconception. Though his work makes it evident that such varieties may exist, it is very unlikely that Mendel could have had seven pairs of varieties such that the members of each pair differed from each other in only one considerable character. The point is probably one of little theoretical or practical consequence, but a rather heavy stress is laid on the word wesentlich." Most practical experimenters will feel the weight of this difficulty. Unless Mendel had known in advance of the separate inheritance of the characters he was studying he could scarcely have used seven such pairs of varieties. More probably, perhaps, he would have used fewer varieties, say four or five, and crossed these in all, six or ten, possible ways. In any case, we should expect that some or all of the crosses would have involved more than one contrasted pair of characters. Each progeny would then have segregated in more than one factor, and the question arises as to what Mendel did with these additional data. Two courses seem possible : (i) He might, for each cross, have chosen arbitrarily one factor, for which that particular cross was regarded as an experiment, and ignored segregation in other factors. (ii) He might have scored each progeny in all the factors segregating, a**embled the data for each factor from the different crosses in which it was involved, and reported the results for each factor as a single experiment. The first course seems incredibly wasteful of data. This objection is not so strong as it might seem, since it can be shown that Mendel left uncounted, or at least unpublished, far more material than appears in his paper. He evidently felt no anxiety lest his counts should be regarded as insufficient to prove his theory. But, apart from being wasteful, to have adopted this course would seem to imply as much foreknowledge of the outcome as if he had deliberately chosen unifactorial crosses. It would seem in any case an extremely arbitrary course to take. The second course is in effect what most modern geneticists would do, unless they were discussing either the linkage or the interaction of more than one factor. Mendel nowhere gives summaries of the aggregate frequencies from different experiments, and this would be intelligible if the "experiments" reported in the paper were fictitious, being in reality themselves such summaries. Mende l's paper is, as has been frequently noted, a model in respect of the order and lucidity with which the successive relevant facts are presented, and such orderly presentation would be much facilitated had the author felt himself at liberty to ignore the particular crosses and years to which the plants contributing to any special result might belong. Mendel was an experienced and successful teacher, and might well have adopted a style of presentation suitable for the lecture-room without feeling under any obligation to complicate his story by unessential details. The style of didactic presentation, with its conventional simplifications, represents, as is well known, a tradition far more ancient among scientific writers than the more literal narratives in which experiments are now habitually presented. Models of the former would certainly be more readily accessible to Mendel than of the latter. The great objection to the view suggested by Bateson's hint, that Mendel's "experiments" are fictitious, and that his paper is a didactic exposition embodying his accumulated data, lies in the words which Mendel himself used in introducing the successive steps of his account, e.g., at the beginning of the eighth section (p. 332) "The next task consisted in ascertaining ....", and the opening sentence of the ninth section (p. 338) "The results of the experiments previously described led to further experiments". It is true that the different experiments described are not numbered in a single series ; those described in any one section are numbered afresh 1, 2, 3, . . . . , so that these numbers were certainly a**igned when the account was written ; also we are never told in what year different plants were grown ; yet, if Mendel is not to be taken literally, when he implies that one set of data was available when the next experiment was planned, he is taking, as redacteur, excessive and unnecessary liberties with the facts. Moreover, the style throughout suggests that he expects to be taken entirely literally ; if his facts have suffered much manipulation the style of his report must be judged disingenuous. Consequently, unless real contradictions are encountered in reconstructing his experiments from his paper, regarded as a literal account, this view must be preferred to all alternatives, even though it implies that 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 first and chief paper. Such a reconstruction is attempted in the next section.