Bateson and his form of Mendelism
Updated: May 22, 2022
William Bateson was critical of the biometricians’ statistical methods, especially Karl Pearson’s. Bateson associated Mendelism with discontinuous evolution which is opposed to the biometrician’s view that evolution is continuous, and Bateson’s system employed theoretical terms, Mendelian ‘factors’, described as “physiological units of as yet unknown nature” (Bateson and Saunders 1902). Let us look at each of Bateson’s views in turn.
First, Bateson opposed the biometric program which concentrated on continuously varying characters. Bateson had become dissatisfied with the study of continuous variation or what Darwin termed ‘individual differences’. At first, Bateson was timid to publish such anti-Darwinian views because of the overwhelming superiority of Darwinian theories of continuous variation; however, after some time, Bateson’s travels and further research suggested that evolutionary changes were not directly connected to selection pressures caused by differences in environment acting upon continuous variations. Bateson proclaims, “it is difficult to suppose both that the process of Variation has been a continuous one, and also that Natural Selection has been the chief agent in building up the mechanisms of things” (Bateson 1891, p. 128). Bateson concluded that the evidence of discontinuous evolution are few in number but they do represent a sample of what is required to enable us to deal with the problem of descent. Thus, Bateson did not reject the notion of variation, but he thought that ordinary continuous variation was evolutionarily irrelevant and that evolution proceeded via occasional more or less drastic mutations.
Second, Bateson explained the inheritance of attributes and visible hereditary phenomena by reference to the segregation of unseen physiological units. The results of his studies in variation led him to say that a characteristic “is in some unknown way a part of their nature, and is not directly dependent upon Natural Selection at all” (Bateson 1894, p. 573). Bateson believed some experiments in breeding would reveal the ‘unknown part of their nature’. Such experiments, however, concentrated on the very phenomena Pearson and the biometers tried to avoid. The experiments in breeding focused on the method of transmission of variations, something Bateson saw as the essential phenomenon of evolution.
The major difference between the biometricians and the Mendelians was the acceptance of blending versus particulate inheritance. Blending inheritance was the idea that inherited characteristics were blended between the two parental forms. The offspring was an intermediate result of the blending of the two parents. Particulate inheritance, however, involved no blending whatsoever. Particulate inheritance postulated the existence of hereditary particles passed on unchanged from parent to progeny. Bateson advocated the latter view whereby the mechanism of heredity, the gene, is passed unchanged from parent to offspring.
Bateson and the other Mendelians were concerned with interpreting breeding results in terms of particulate theory of inheritance. They seemed to be operating under an assumption about the mechanism of inheritance. Mendelian factors supposedly passed unchanged from parent to offspring. These factors underwent segregation – as demonstrated in his study of fowl – and random distribution. Inheritance of these factors did not involve blending. “Descriptions of these processes relied on straightforward probabilistic analysis together with assumptions about dominance of one fact over another in the visible manifestation of the factors in the offspring. The model of heredity and the methods involved in its application were then used to study the inheritance of specific characteristics in plants and animals” (Morrison 2002, p. 48) Bateson, then, was primarily concerned with attributes in plants and animals and from where these attributes arose. He believed these attributes arose due to discontinuous hereditary factors. This is not to say that Bateson believed or speculated about what these factors are. On the contrary, Bateson seems to dismiss such speculative assumptions. Coleman has also claimed that Bateson never really accepted the notion of a Mendelian factor as a material thing, but Bateson did believe that such entities exist even though we had no idea how to describe them or what constituted them (Coleman 1970, pp. 228-314). Regardless, his views on the nature of variation preclude any compromise position. In an address to the Horticultural Society, Bateson prepared a paper extending his theme that virtually nothing was known about the mechanisms of heredity and variation.
We want to know the whole truth of the matter; we want to know the physical basis, the inward and essential nature, the causes, as they are sometimes called, of heredity. We want also to know the laws which the outward and visible phenomena obey. (Bateson 1900, p. 2)
Bateson had nothing to offer with respect to the ‘causes’ of heredity, but he wanted “to know the whole truth of the matter” and “the physical basis” of heredity. Such comments imply that Bateson thought there was some existent thing that caused variation, but he did not know how to explain or describe it. There was reason to suspect that such factors existed because of the way that they manifested themselves in ‘visible phenomena’, but as for determining what they were composed of was another story. All one could do is speculate as to the composition of such factors. Bateson, recognizing these epistemological inefficiencies, confesses:
Let us recognize from the outset that as to the essential nature of these phenomena we still know absolutely nothing. We have no glimmering of an idea as to what constitutes the essential process by which the likeness of the parent is transmitted to the offspring. We can study the process of fertilization and development in the finest detail which the microscope manifests to us, and we may fairly say that we have now a thorough grasp of the visible phenomena; but of the nature of the physical basis of heredity we have no conception at all. No one has yet any suggestion, any working hypothesis, or mental picture that has thus far helped in the slightest degree to penetrate beyond what we see. We do not know what is the essential agent in the transmission of parental characters, not even whether it is a material agent or not. Not only is our ignorance complete, but no one has the remotest idea how to set to work on that part of the problem. (Bateson 1900, p. 2)
Bateson’s pessimism broke, however, soon after reading deVries’s account of Mendel’s laws of heredity on a train ride to the meetings of the Horticultural Society in 1900. He went so far as to say that Mendel’s principles will “certainly place a conspicuous part in all future discussions of evolutionary problems” (Bateson 1900, p. 8). Bateson merely wanted to make a general prediction encompassing the view of unit-characters. Bateson writes:
It is reasonable to infer that a science of Stoechiomety will now be created for living things, a science which shall provide an analysis, and an exact determination of their constituents. The units with which that science must deal, we may speak of, for the present, as character-units, the sensible manifestations or physiological units of as yet unknown nature. (Bateson and Saunders 1902)
According to Bateson, we can only assume that a unit-character is present by virtue of observing certain ‘sensible manifestations’. In this sense, we can only describe what occurs in an experiment and infer from that evidence that such unit-characters or Mendelian factors are present. Even though we have a limited amount of evidence of their existence, we can assume that something is present to cause variation. Such speculation seems unwarranted. To infer that something exists at the micro-level because we can observe change at the macro-level seems unsupportable. Bateson is careful not to assume too much. For instance, he only wants to say that something exists even though we do not have the means to observe such entities. In the above quotation, he says these entities are something of an ‘as yet unknown nature’. This sounds as if Bateson is saying we somehow now lack the ability to observe these entities, but we will soon be able to observe them in the future. Pearson, however, rejected this idea. Bateson did not speculate about the characteristics of these unknown entities, thus circumventing the issue of what constitutes these entities.
In the end, it appears that Bateson does not forthrightly reject the existence of theoretic nonveridical entities. He merely assumes we cannot observe them, but, by using something similar to the principle of instrumentalism, he believes we can infer that something exists which causes variation in organisms. To suppose that something caused variation in organisms was acceptable since such causal factors were inferred from direct observation, but to suppose that something caused variation in organisms a priori was unacceptable for Bateson. In other words, Mendelism contained nothing like a ‘universal law’ that some unobservable, unknowable entity actually existed. Unlike Pearson who was agnostic with respect to the supersensuous and whose theory emphasized description over explanation, Bateson wanted to explain genetic inheritance without going so far as postulating the constitution of theoretic entities.
The main thrust of Bateson’s program consisted of elucidating the characters responsible for variation. His main suggestion proffered that new characters are produced by biological processes and persist whether or not they are of use to the organism. The experiments he performed were meant to clarify an understanding of how Mendelian factors behave. His experiments, however, were not supposed to show what Mendelian factors are. Their behavior and constitution are two separate issues; the one that concerned Bateson was the former, not the latter. The inevitability of Bateson producing a theory of factors solely through their behavior with complete disregard for their constitution is utterly impossible. A future blog post shall concern the implications of both Bateson’s and Pearson’s implicit acceptance of Mendelian factors; one more than the other, but acceptance nonetheless.