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Popper’s Darwinian Analogy
Popper famously held that the growth of scientific knowledge and the Darwinian mechanism of trial and error elimination are analogous processes. Both the validity of this analogy and Popper’s interpretation of what this Darwinian mechanism consists in have been criticized. But it has been ignored that the use of Popper’s Darwinian analogy had changed in the course of Popper’s life. I will argue that until the 1960s, he used the Darwinian process as a model for understanding the growth of scientific knowledge, whereas from the 1960s on, the explanatory order was reversed: he used his new insights about the growth of scientific knowledge to say something about the real nature of Darwinian selection. In short, this analogy was so central for Popper’s thinking that rather than giving up this analogy, he tried very hard to find theories of biological evolution that would make this analogy plausible. And this is what led him to make somewhat surprising claims about the nature of selection as well as to flirt with Lamarckism.
One of the most deeply entrenched ideas in Popper’s philosophy is the analogy between the growth of scientific knowledge and the Darwinian mechanism of natural selection. Popper gave his first exposition of these ideas very early on. In a letter to Donald Campbell,1 Popper says that the idea goes back at least to the early thirties.2 And he had a fairly detailed account of it in his ‘What is dialectic?’, a talk given in 1937 and published in 1940:3
If we want to explain why human thought tends to try out every conceivable solution for any problem with which it is faced, then we can appeal to a highly general sort of regularity. The method by which a solution is approached is usually the same; it is the method of trial and error. Thus, fundamentally, is also the method used by living organisms in the process of adaptation (Popper 1940/1963, p. 312).
And here is the famous exposition of the general idea of the analogy between theory choice and natural selection in the Logic of Scientific Discovery:
How and why do we accept one theory in preference to others? […] We choose the theory which best holds its own in competition with other theories; the one which, by natural selection, proves itself the fittest to survive. This will be the one which not only has hitherto stood up to the severest tests, but the one which is also testable in the most rigorous way. (Popper 1959/2002, p. 91.)
And he gave a detailed account of this analogy in his last book (Popper 1994). So it seems that the analogy between the growth of scientific knowledge and the Darwinian mechanisms of natural selection were central to his philosophy throughout his life.
In fact, I will argue that this analogy was so central that rather than giving up this analogy, Popper tried very hard to find theories of biological evolution that would make this analogy plausible. And this is what explains his often dismissed and misinterpreted flirtation with Lamarckism.
I will argue that until the 1960s, Popper used the Darwinian process as a model for understanding the growth of scientific knowledge. He took the Darwinian model for granted and applied it in the case of the growth of scientific knowledge. From the 1960s, the explanatory order was reversed. He no longer took the Darwinian model for granted, but rather used his new insights about the growth of scientific knowledge to figure out the real nature of Darwinian selection. And this led him to make some dubious and widely criticized claims about the biological domain (including a rarely publicized aborted attempt to publish in defence of Lamarckism in Nature).
The plan of this paper is the following. First, I outline the main similarities, as Popper perceived them, between the growth of scientific knowledge and the Darwinian mechanism for natural selection (Section II) and point out how Popper’s picture of one side of this analogy, the growth of scientific knowledge, got more complex during the 1960s, arguably, as a result of his interaction with Lakatos and Zahar (Section III). I aim to point out how, in order to preserve the Darwinian analogy in the light of his new way of thinking about the growth of scientific knowledge, he had to reinterpret what he took to be the Darwinian model of natural selection (Section IV and V). Finally, I briefly examine whether and how the Darwinian analogy that Popper held to be so important could be salvaged in a biologically plausible manner (Section VI).
II. The Darwinian analogy
There is no shortage of passages in Popper’s writings that emphasize the similarities between the growth of scientific knowledge and the Darwinian mechanism for natural selection. The question is what these passages say about the nature of this similarity. The main point of analogy seems to be that both the growth of scientific knowledge and the Darwinian mechanisms are selection processes (to be contrasted with instruction): they consist of ‘random’ (more on this soon) trials followed by error-elimination.
Here is how it works in the biological case. Selection is often4 described as repeated cycles of two separate processes. As Ernst Mayr says, “natural selection is actually a two-step process, the first one consisting of the production of genetically different individuals (variation), while the survival and reproductive success of these individuals is determined in the second step, the actual selection process (Mayr 1991, p. 68, see also Mayr 1982, pp. 519-520, Mayr 2001, p. 117 and Mayr 1978).5 David Hull calls these two steps replication and interaction (cHull 1981, Hull 1988, Hull et al. 2001).6 He defines selection as:
The repeated cycles of replication and environmental interaction so structured that environmental interaction causes replication to be differential. (Hull et al. 2001, p. 53)
Popper’s claim is that this model also applies to the growth of scientific knowledge. Scientists form bald conjectures: this is the first step of replication (Hull) or variation (Mayr). And then they subject these conjectures to falsification: this is the second step of environmental interaction (Hull) or ‘actual selection’ (Mayr).
Thus, as the selection process consists of two steps, the analogy between selection among scientific theories and natural selection could be broken down into two different aspects: (i) the analogy between the formation of conjectures and replication and (ii) the analogy between falsification and environmental interaction. I will put (ii) aside, although it has been famously argued that this analogy is at best misleading: theories do not get falsified in the way organisms die: the death of theories is a slow one (see Lakatos 1970 for the most famous exposition of this idea). Note however that the Darwinian analogy does not imply that the second step of environmental interaction brings either death or survival. There can be selection even if the second step of environmental interaction only influences the number of offspring the competing organisms have (see, e. g., Williams 1966). But the main focus of Popper’s Darwinian analogy is not (ii), but (i).
Popper’s original insight was that just as the first step of natural selection (replication, variation) is random, the conjectures of science are also random. And just as any kind of evolutionary change is only achieved with the contribution of the second step of selection (environmental interaction), the same is true for the growth of scientific knowledge, which could not happen without the second step of error-elimination.
And here we need to make a distinction between the early (pre-1960s) Popper and the late Popper. To state the difference very simply, the early Popper takes it for granted that mutation is random and concludes from the Darwinian analogy that conjectures are also random (see esp. Popper 1959, p. 31). The late Popper, in contrast, no longer takes conjectures to be (fully) random and looks for ways in which mutations could be interpreted as not (completely) random.
III. Popper’s revisions of the Darwinian analogy
The original version of Popper’s Darwinian analogy took the model of random variation from biology and applied it to the formation of conjectures. If this process is random, then there can be no logical analysis thereof. As Popper emphasizes in the Logic of Scientific Discovery:
The act of conceiving a theory seems to me neither to call for logical analysis nor to be susceptible of it. The question how a new idea occurs to a man – whether it is a musical theme, a dramatic conflict, or a scientific theory – […] is irrelevant to the logical analysis of scientific knowledge (Popper 1959, p. 31).
Even in his first thorough and detailed exposition of the Darwinian analogy, ‘Evolution and the tree of knowledge’, which was originally delivered as the Herbert Spencer lecture in Oxford in 1961 and most of the text was not changed before its publication as Chapter Seven in Objective Knowledge in 1972, he repeatedly talks about “purely accidental co-operation of independent mutations” (Popper 1961/1972, p. 273), “purely accidental mutation” (Popper 1961/1972, p. 270), “independent accidental mutations” (Popper 1961/1972, p. 270) and applies this model to the formation of scientific conjectures.
The problem is that random formation of conjectures just does not seem to be the way science proceeds and some important philosophers in Popper’s circle in the 1960s were giving convincing arguments and thorough analyses of actual case studies that demonstrated this. The most important of these was Imre Lakatos.
Lakatos is very explicit that scientific research programmes are not sets of theories but “a temporal chain of sets of theories”.7 If a scientific research programme faces an objection, it lives on (maybe acquiring a bit of protective belt). In other words, scientific research programmes can and do change. The set of theories in a scientific research programme at time t is different from the set of theories in it at some later time, t*. And what set of theories we get in a research programme at time t* depends on what happens to the research programme at time t – what objections it faces and how it can handle them.
Thus, Lakatos’s scientific research programmes can be gradually fine-tuned: the set of theories that comprise the research programme at time t* can deal with more objections than the set of theories at time t, which precedes t*. The ‘mutations’ of the research programme are not completely ‘blind’ in the sense Popper thinks genetic mutations are blind: it is not the case that “the survival of a mutation cannot influence the further mutations” (Popper 1975/1996, p. 5). In the case of a scientific research programme, the way it can deal with objections does influence what directions it develops into in the future.
Given how close Popper and Lakatos were intellectually in the mid-1960s, it is unlikely that these ideas would not have had an influence on Popper, especially given his claim about Lakatos: “I can say what I think about him in five words: He has revolutionized my thinking”.8 And Lakatos clearly thought that his ideas had influenced Popper: he wrote repeatedly (at least a dozen times) on the margins of various manuscripts by Popper that, “you are stealing from me”.9 It is also likely that Lakatos’s perception that Popper did not acknowledge his influence was the main cause of the serious fallout between the two philosophers in the early seventies.10
But Lakatos was not the only philosopher in Popper’s circle in the 1960s who argued that the formation of conjectures is not to be compared to ‘purely accidental independent mutations’. Others included Elie Zahar and John Worrall. Zahar argued that even the boldest conjectures could be given a logical analysis in gradualistic terms (see especially Zahar 1984) and Worrall (much later) gave a detailed case study of Fresnel’s theory of diffraction, which shows that his conjectures were not at all random (Worrall 1995, pp. 92ff, see also Akeroyd 2004, pp. 390-393 for an alternative analysis).
To sum up, it seems that, under the influence of all these philosophers, Popper changed his mind about the completely random character of the formation of scientific conjectures some time in the 1960s. And this change was already reflected in his 1965 Compton lecture, where he writes:
The method of trial and error-elimination does not operate with completely chance-like or random trials […], even though the trials may look pretty random. […] For the organism is constantly learning from its mistakes, that is, it establishes controls which suppress or eliminate, or at least reduce the frequency of, certain possible trials (which were perhaps actual ones in its evolutionary past (Popper 1965/1972, p. 245, n. 55).11
Popper spent a lot of time in the next decade trying to spell out in what sense the formation of conjectures is random and in what sense it is not (some examples: Popper 1974b, p. 1061, Popper 1978, p. 348, Popper 1974a, p. 138, (Popper 1975/1996, p. 3).
But if he no longer took the formation of scientific conjectures to be completely random, then how could he hold on to the Darwinian analogy? There are two options: first, he could limit the generality of the analogy and allow for the differences between mutations and conjectures while preserving the general structure of the analogy. And, second, he could revise the way to interpret mutations in such a way that the analogy between conjectures and mutations is restored. Popper seems to have tried both of these strategies.
He made a number of attempts to clarify how the ‘more or less random’ character of mutations is different from the ‘more or less random’ character of conjectures. According to the most detailed such attempt, in his 1973 Herbert Spencer Lecture (Popper 1975/1996, p. 5), mutations are (more or less) random and also blind, whereas conjectures are although still (more or less) random, they are not blind. This way of drawing the distinction seems to contradict his Popper 1974b, p. 1061 (written in the same year as the Spencer lecture), where he describes scientific conjectures as blind and even elaborates on what this means and how it does not exclude goal-directedness. All of these distinctions and alleged clarifications, regardless of how problematic, ad hoc or contradictory they may be, are only supposed to be supplementary of Popper’s more fundamental reinterpretation of the Darwinian analogy. Popper recognized that the formation of scientific conjectures is not completely random and his insistence on the Darwinian analogy forced him to say the same about mutations. He did try to point out some important differences between the two processes, but these are supposed to be differences between two not completely random processes.
But then Popper had to reinterpret the theory of natural selection in such a way that mutations would come out as not completely random. And this required some adventures, not always very fortunate ones, into the domain of biology.
IV. Popper’s adventures into the domain of biology
In the 1960s, Popper was apparently quite preoccupied with various questions in evolutionary biology. In 1963, he asks Campbell for all of his papers on evolutionary epistemology.12 In 1965, Lakatos says in a letter to Marjorie Grene, somewhat despairingly, that “nowadays, [Popper’s] main interest is evolution”.13
The focus of Popper’s interest was the question about how random mutations can explain the apparent teleology of the natural world. This theme appeared in his 1961 lecture:
[The difficulty evolutionary theory faces is] the difficulty of understanding how a complicated organ, such as the eye, can ever result from the purely accidental co-operation of independent mutations. (Popper 1961/1972, p. 273.)
And, even more explicitly:
The real difficulty of Darwinism is the well-known problem of explaining evolutions which are apparently goal-directed such as that of our eyes, by an incredibly large number of very small steps; for according to Darwinism, each of these steps is the result of a purely accidental mutation. That all these independent accidental mutations should have had survival value is difficult to explain. (Popper 1961/1972, pp. 269-270.)
Popper tried to give an answer to this question in a number of ways. But it is important to note that the reason why he was interested in these questions about evolutionary biology was the need to reinterpret his Darwinian analogy. Two of his most infamous attempts to explain how adaptive evolution is possible in spite of the randomness of mutations were the ‘hopeful behavioural monsters hypothesis’ (based on Goldschmidt 1940) and the ‘double spearhead hypothesis’, which postulates two different kinds of genes that are subject to selection in different manner. Both of these ideas are already present in Popper 1961/1972 (the latter in the original 1961 lecture, the former only in the addendum written before the publication in 1972).
Both of these ideas were (rightly) dismissed by Popper’s contemporaries. So much so that Popper’s close friend, Peter Medawar repeatedly discouraged Popper from publishing both the Spencer lecture and later the Compton lecture (“Of clouds and clocks” (Popper 1965/1972)), where he repeated the ‘double spearhead hypothesis’.14 Ernst Mayr was equally negative: “To be very frank, I was not too happy with your treatment of natural selection in the essay you wrote in Objective Knowledge”.15 Popper seems to have abandoned his ‘behavioural monster’ idea, but he did reiterate the ‘double spearhead hypothesis’ throughout the rest of his life, even in Popper 1994. What this lead to was a certain amount of bewilderment and mistrust towards Popper’s ideas on behalf of biologists (see Hull 1999 for a thorough summary, but see also Settle 1996). As John Worrall summarizes, Popper “interprets ‘selection’ in a way that is, to say the least, rather unorthodox” (Worrall 1995, p. 102).
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