The early history of chance in evolution

Highlights

• History and philosophy of biology often use chance, randomness, and similar terms.

• The usual history focuses on the introduction and objectivity of chance in evolution.

• The work of Galton, Pearson, and Weldon does not respond to these questions.

• The theory/world relationship offers a better lens for analyzing chance in evolution.

Abstract

Work throughout the history and philosophy of biology frequently employs ‘chance’, ‘unpredictability’, ‘probability’, and many similar terms. One common way of understanding how these concepts were introduced in evolution focuses on two central issues: the first use of statistical methods in evolution (Galton), and the first use of the concept of “objective chance” in evolution (Wright). I argue that while this approach has merit, it fails to fully capture interesting philosophical reflections on the role of chance expounded by two of Galton's students, Karl Pearson and W.F.R. Weldon. Considering a question more familiar from contemporary philosophy of biology—the relationship between our statistical theories of evolution and the processes in the world those theories describe—is, I claim, a more fruitful way to approach both these two historical actors and the broader development of chance in evolution.

Introduction

Our discussions of the history and philosophy of evolutionary biology continually make use of terms that may broadly be described as falling under the umbrella of ‘chance’: ‘unpredictability’, ‘randomness’, ‘stochasticity’, and ‘probability’ provide only a few examples. We find extensive discussion in the history of biology concerning the introduction of statistical methods in the life sciences (see, e.g., Porter, 1986, Sheynin, 1980). In the spirit of integrating the history and philosophy of science, however, it is notable that the corresponding question about these concepts often goes unanswered. How were the various notion of ‘chance’ now so prevalent in the biological literature introduced into evolutionary theorizing?

One of the only serious attempts to describe both facets of this historical transformation was advanced by Depew and Weber (1995), and has since been found in various places throughout the history and philosophy of biology. Their picture of the development of chance in evolution seeks to understand two crucial historical events. First, when and how did evolutionary theorizing become statistical? Second, when and how did such theories come to be taken to describe “genuinely chancy” processes in the world?¹

Elucidating this standard view is the project of my second section. Francis Galton, it is generally recognized, is responsible for the first, methodological shift—it was Galton's work on the statistically derived law of ancestral heredity that introduced statistics into the study of evolution. The second, conceptual shift originates in Sewall Wright's shifting balance theory, which required a much more significant role for a chancy process of genetic drift than the theories which had come before it.

After introducing Depew and Weber's view, we will explore it in more detail. Section 3 will return to Darwin's own works, to establish the now-standard interpretation that Darwin believed evolution to be a non-statistical theory of non-objectively-chancy processes in the world. We then turn to Francis Galton in Section 4, where I describe his role in the development of the first statistical methods in the study of evolution. Rather than moving on to Wright, however, we will examine in Section 5 two of Galton's students at the end of the nineteenth century, Karl Pearson and W.F.R. Weldon. On Depew and Weber's view, these two would be minor characters.

Why, then, consider Pearson and Weldon at all? It is their work that will serve as our point of departure from considering the introduction of chance in terms of Depew and Weber's two focal historical moments. I will argue that if we are interested in the emergence of chance in evolution, Pearson and Weldon should indeed not be read as minor players. A vitally important distinction can be detected in Weldon and Pearson's writings on the philosophical justification for the use of concepts of chance. Suitably considered, that is, we can see Pearson and Weldon as innovators not merely in the use of statistical methodology, but in the philosophical grounding for the use of chance as well. If we focus only on the two events of the Depew and Weber view, we will entirely fail to recognize this aspect of their thought. We must look, then, for a new context for this historical development—a new driving question on which we are able to understand the eventual philosophical rift between Pearson and Weldon. I will argue that this distinction can be best exposed by considering the relationship between our statistical theories and the processes which those mathematical frameworks are intended to describe.

As regards this new question, then, a more mathematical, more positivist school of thought, with Pearson at its head, takes these statistics to be a tool for glossing over the (complex, possibly deterministic or indeterministic) causal details of biological systems. On the other side, a more empiricist, experimentally inclined school, with Weldon at its head, takes these statistics to be an essential way of grasping the full causal detail of biological systems. We can thus see here, I claim, a dramatic difference in the understanding of the connection between evolutionary theories and the evolutionary process, positions that are better comprehended not by way of the “reification” or “objectification” of chance, but by considering their differing views on the relationship between evolutionary theory and the biological world. And this question, as I will briefly argue in the conclusion, resonates strongly with contemporary work in the philosophy of biology.