the early history of chance in evolution: causal and statistical in the 1890s
DESCRIPTION
The traditional history of the understanding of chance in evolution, as told by those like Depew and Weber (1995), goes roughly as follows: for Darwin, evolution is a non-statistical theory (because Darwin predates statistics) of a non-chancy process (natural selection, taken to be analogous to artificial selection). Francis Galton introduces statistics into the study of evolutionary theory in his work on regression and the Law of Ancestral Heredity. Sewall Wright, then, introduces a more robust notion of chancy evolutionary processes when he proposes that drift, in his shifting-balance model, is capable of actively, yet probabilistically, driving populations down the adaptive landscape, away from a selective optimum. This history thus asks two questions: (1) When did evolutionary theory become statistical? (2) When did evolutionary processes come to be seen as chancy? While both these questions are certainly interesting and while the two standard answers to them may well be correct I argue that they miss a vital shift in thinking about chance in biology that was happening well before Sewall Wright. Two of Galton's students, W.F.R. Weldon and Karl Pearson, founded what would come to be known as the biometrical school, dedicated to the statistical study of evolutionary phenomena. Further, they both spent extensive time considering the philosophical grounding of their statistical study of biology. The concerns they had, however, do not map cleanly onto the two questions asked by the standard history: on each of these questions, Weldon and Pearson appear to differ very little from the views of their mentor Galton. I argue, then, that it is time to deploy a new perspective when evaluating the views of these early evolutionists. Rather than searching for the ontic or reified sort of chance implied by the standard history's question (2), we can find more profitable results if we consider the work of those like Weldon and Pearson from a different angle: What is the relationship between (statistical) biological theories and the processes they describe? Further, when we examine the positions of Pearson and Weldon on this question, we find both that the two men, who are commonly thought to agree on nearly all points of interest, diverge in important and significant ways, and that this divergence parallels a heated debate in contemporary philosophy of biology: that between causal and statistical interpretations of natural selection, fitness, and genetic drift.TRANSCRIPT
University of Notre DameProgram in the History and Philosophy of Science
Department of Philosophy
The Early History of
‘Chance’ in Evolution
HOPOS 2012, Halifax, Canada
Charles H. [email protected]
A Talk in Three Acts
• Act I: The “standard” historical narrative of chance inevolution
• Act II: A problem for the standard narrative: Pearson andWeldon
• Act III: A speculative philosophical conclusion
A Talk in Three Acts
• Act I: The “standard” historical narrative of chance inevolution
• Act II: A problem for the standard narrative: Pearson andWeldon
• Act III: A speculative philosophical conclusion
A Talk in Three Acts
• Act I: The “standard” historical narrative of chance inevolution
• Act II: A problem for the standard narrative: Pearson andWeldon
• Act III: A speculative philosophical conclusion
The “Standard History”
• Two questions:
1. When did evolutionbecome a statisticaltheory?
2. When did evolutionbecome a theory of“genuinely chancy”processes?
The “Standard History”
• Two questions:1. When did evolutionbecome a statisticaltheory?
2. When did evolutionbecome a theory of“genuinely chancy”processes?
The “Standard History”
• Two questions:1. When did evolutionbecome a statisticaltheory?
2. When did evolutionbecome a theory of“genuinely chancy”processes?
Some Preliminaries: Darwin
Origin (1859), p. 106
Some Preliminaries: Darwin
Origin (1859), p. 106
Question 1: Francis Galton
Question 1: Francis Galton
The principle on which the action of the apparatusdepends is, that a number of small and independentaccidents befall each shot in its career. In rare cases,a long run of luck continues to favour the course of aparticular shot towards either outside place, but inthe large majority of instances the number ofaccidents that cause Deviation to the right, balance ina greater or less degree those that cause Deviation tothe left. […] This illustrates and explains whymediocrity is so common.
Galton, Natural Inheritance (1889), pp. 64–65
Question 2: Sewall Wright
From Provine, Sewall Wright and Evolutionary Biology
Question 2: Sewall Wright
From Provine, Sewall Wright and Evolutionary Biology
A Problematic: Pearson & Weldon
Traditional Questions: Pearson
In our ignorance we ought to consider beforeexperience that nature may consist of all routines, allanomalies, or a mixture of the two in any proportionwhatever, and that all such are equiprobable....
Pearson, Grammar of Science, 1st ed. (1892), p. 172
Traditional Questions: Pearson
In our ignorance we ought to consider beforeexperience that nature may consist of all routines, allanomalies, or a mixture of the two in any proportionwhatever, and that all such are equiprobable....
Pearson, Grammar of Science, 1st ed. (1892), p. 172
Traditional Questions: Weldon
All experience, which we are obliged to deal withstatistically, is experience of results which dependupon a great number of complicated conditions, somany and so difficult to observe that we cannot tell inany given case what their effect will be.
Weldon, “Inheritance in Animals and Plants” (1906), p. 97
Pearson & Weldon on Chance
• Pearson and Weldon theorize extensively about their useof chance
• This theorizing is not captured by the two “traditional”questions
• It provides us the historical impetus we need to build anew framework for understanding chance
Pearson & Weldon on Chance
• Pearson and Weldon theorize extensively about their useof chance
• This theorizing is not captured by the two “traditional”questions
• It provides us the historical impetus we need to build anew framework for understanding chance
Pearson & Weldon on Chance
• Pearson and Weldon theorize extensively about their useof chance
• This theorizing is not captured by the two “traditional”questions
• It provides us the historical impetus we need to build anew framework for understanding chance
Pearson & Weldon on Chance
• Pearson and Weldon theorize extensively about their useof chance
• This theorizing is not captured by the two “traditional”questions
• It provides us the historical impetus we need to build anew framework for understanding chance
Pearson & Weldon on Chance
1. What was the content of Pearson’s and Weldon’sphilosophical work on chance?
2. What is the right way to understand their philosophicalproject?
Pearson & Weldon on Chance
1. What was the content of Pearson’s and Weldon’sphilosophical work on chance?
2. What is the right way to understand their philosophicalproject?
Pearson and Biometry
[The last step of the scientific method is] thediscovery by aid of the disciplined imagination of abrief statement or formula, which in a few wordsresumes the whole range of facts. Such a formula…istermed a scientific law. The object served by thediscovery of such laws is the economy of thought.
Pearson, Grammar of Science, 1st ed. (1892), p. 93
Pearson and Biometry
[The lack of progress in biology is] largely owing to acertain prevalence of almost metaphysical speculationas to the causes of heredity, which have usurped theplace of that careful collection and elaborateexperiment by which alone sufficient data might havebeen accumulated, with a view to ultimatelynarrowing and specialising the circumstances underwhich correlation was measured.
Pearson, “Mathematical Contributions to the Theory of Evolution.III. Regression, Heredity, and Panmixia” (1896), p. 255
Weldon on Statistics
If we want to make a statement about the stature ofEnglishmen, we must find a way of describing ourwhole experience; we must find some simple way ofdescribing our whole experience, so that we caneasily remember and communicate to others howmany men of any given height we find among athousand Englishmen. We must give up the attemptto replace our experiences by a simple average valueand try to describe the whole series of results ourobservation has yielded.
Weldon, “Inheritance in Animals and Plants” (1906), p. 94
Weldon on Cause
Prof. Weldon declared, with some expressions of reluctance andregret – due, as he was good enough to say, from an old pupilto the teacher whom he is about to denounce and demolish –that to attempt to say which of two or more correlated growthsis the cause of survival is unreasonable, and that when Isuggested, even as a matter for consideration, that a certaingerm-slaying quality in phagocytes accompanying a pigmentedskin, rather than the pigment itself in the skin, is the cause ofthe survival of dark-skinned people in malarial regions, I was“absolutely illogical.” “It is,” said Prof. Weldon, “impossiblelogically to separate these two correlated phenomena. Thecoloured skin is as much a cause of the survival of the dark manas is the germ-destroying property of his blood.”
E. Ray Lankester, “Are Specific CharactersUseful? [letter]” Nature 54:1394 (1896), p. 245
Pearson vs. Weldon
On the second point [causation], surelyProf. Lankester is entirely in the right? It is notsufficient to show that there is a correlation betweena certain frontal ratio and death-rate in order toassert that the frontal ratio is a cause of death-rate.Very probably it may be, but the definition is notlogically complete, or at any rate a definition of causehas been adopted which does not appear of muchutility to science.
Pearson, “The Utility of Specific Characters [letter]”Nature 54:1403 (1896), pp. 460–461
Pearson & Weldon on Chance
Pearson:• Positivist role of science for the economy of thought• Statistics as a tool for simplification of data• Causation as precise mathematical law (think Newton)
Weldon:• Science as the maximally complete description of nature• Statistics as a tool to capture all causal influences• Causation = correlation (and experiments sharpen ourcorrelations)
Asking the Right Question
What is the relationship between statistical scientific theoriesand the processes those theories intend to describe?• Pearson: acausal, anti-realist view of biological theories• Weldon: statistical theories as causal descriptions of theworld
Asking the Right Question
What is the relationship between statistical scientific theoriesand the processes those theories intend to describe?
• Pearson: acausal, anti-realist view of biological theories• Weldon: statistical theories as causal descriptions of theworld
Asking the Right Question
What is the relationship between statistical scientific theoriesand the processes those theories intend to describe?• Pearson: acausal, anti-realist view of biological theories
• Weldon: statistical theories as causal descriptions of theworld
Asking the Right Question
What is the relationship between statistical scientific theoriesand the processes those theories intend to describe?• Pearson: acausal, anti-realist view of biological theories• Weldon: statistical theories as causal descriptions of theworld
Speculative Philosophical Coda
The “causalist/statisticalist debate” in the philosophy ofbiology:
• Causalist: Biological theories describe causal processes ofnatural selection and genetic drift
(Hodge, Beatty, Finsen, Millstein,Stephens, Ramsey, Abrams, Otsuka, Turner, Allen, Lloyd)
• Statisticalist: Biological theories are merely statisticalsummaries of genuinely causal individual-level events
(Walsh, Matthen, Ariew, Lewens, Ernst, Krimbas, Brunnander)
Speculative Philosophical Coda
The “causalist/statisticalist debate” in the philosophy ofbiology:• Causalist: Biological theories describe causal processes ofnatural selection and genetic drift
(Hodge, Beatty, Finsen, Millstein,Stephens, Ramsey, Abrams, Otsuka, Turner, Allen, Lloyd)
• Statisticalist: Biological theories are merely statisticalsummaries of genuinely causal individual-level events
(Walsh, Matthen, Ariew, Lewens, Ernst, Krimbas, Brunnander)
Speculative Philosophical Coda
The “causalist/statisticalist debate” in the philosophy ofbiology:• Causalist: Biological theories describe causal processes ofnatural selection and genetic drift
(Hodge, Beatty, Finsen, Millstein,Stephens, Ramsey, Abrams, Otsuka, Turner, Allen, Lloyd)
• Statisticalist: Biological theories are merely statisticalsummaries of genuinely causal individual-level events
(Walsh, Matthen, Ariew, Lewens, Ernst, Krimbas, Brunnander)
Speculative Philosophical Coda
The “causalist/statisticalist debate” in the philosophy ofbiology:• Causalist: Biological theories describe causal processes ofnatural selection and genetic drift (Hodge, Beatty, Finsen, Millstein,Stephens, Ramsey, Abrams, Otsuka, Turner, Allen, Lloyd)
• Statisticalist: Biological theories are merely statisticalsummaries of genuinely causal individual-level events(Walsh, Matthen, Ariew, Lewens, Ernst, Krimbas, Brunnander)
Speculative Philosophical Coda
Pearson and Weldon’s question: What is the relationshipbetween statistical scientific theories and the processes thosetheories intend to describe?
Causalist/statisticalist question: The same?
Odd case: historical case responds better to contemporaryquestions than to historical questions?
Speculative Philosophical Coda
Pearson and Weldon’s question: What is the relationshipbetween statistical scientific theories and the processes thosetheories intend to describe?
Causalist/statisticalist question: The same?
Odd case: historical case responds better to contemporaryquestions than to historical questions?
Speculative Philosophical Coda
Pearson and Weldon’s question: What is the relationshipbetween statistical scientific theories and the processes thosetheories intend to describe?
Causalist/statisticalist question: The same?
Odd case: historical case responds better to contemporaryquestions than to historical questions?
