Roberta L. Millstein

Alexander Rosenberg (1994) claims that the omniscient viewpoint of the evolutionary process would have no need for the concept of random drift. However, his argument fails to take into account all of the processes which are considered to be instances of random drift. A consideration of these processes shows that random drift is not eliminable even given a position of omniscience. Furthermore, Rosenberg must take these processes into account in order to support his claims that evolution is deterministic and that evolutionary biology is an instrumental science.

This chapter provides an introduction to the study of the philosophical notions of mechanisms and causality in biology and economics. This chapter sets the stage for this volume, Mechanism and Causality in Biology and Economics, in three ways. First, it gives a broad review of the recent changes and current state of the study of mechanisms and causality in the philosophy of science. Second, consistent with a recent trend in the philosophy of science to focus on scientific practices, it in turn implies the importance of studying the scientific methods employed by researchers. Finally, by way of providing an overview of each chapter in the volume, this chapter demonstrates that biology and economics are two fertile fields for the philosophy of science and shows how biological and economic mechanisms and causality can be synthesized.

Elsewhere, I defend the “causal interactionist population concept” (CIPC). Here I further defend the CIPC by showing how it clarifies another concept that biologists grapple with, namely, environment. Should we understand selection as ranging only over homogeneous environments or, alternatively, as ranging over any habitat area we choose to study? I argue instead that the boundaries of the population dictate the range of the environment, whether homogeneous or heterogeneous, over which selection operates. Thus, understanding the concept of population helps us to understand concepts of selective environment, exemplifying the importance of the CIPC to other concepts and debates.

Biologists and philosophers have been extremely pessimistic about the possibility of demonstrating random drift in nature, particularly when it comes to distinguishing random drift from natural selection. However, examination of a historical case-Maxime Lamotte's study of natural populations of the land snail, Cepaea nemoralis in the 1950s - shows that while some pessimism is warranted, it has been overstated. Indeed, by describing a unique signature for drift and showing that this signature obtained in the populations under study, Lamotte was able to make a good case for a significant role for drift. It may be difficult to disentangle the causes of drift and selection acting in a population, but it is not impossible

Biologists and philosophers have offered differing concepts of biological race. That is, they have offered different candidates for what a biological correlate of race might be; for example, races might be subspecies, clades, lineages, ecotypes, or genetic clusters. One thing that is striking about each of these proposals is that they all depend on a concept of population. Indeed, some authors have explicitly characterized races in terms of populations. However, including the concept of population into concepts of race raises three puzzles, all having to do with time. In this paper, I extend the causal interactionist population concept (CIPC) by introducing some simple assumptions about how to understand populations through time. These assumptions help to shed light on the three puzzles, and in the process show that if we want to understand races in terms of populations, we will need to revise our concept(s) of race.

I argue that Binkley et al. use causal process tracing in conjunction with a natural trajectory experiment and two natural snapshot experiments in their re-examination of the Kaibab. This shows that Aldo Leopold may have been right about trophic cascade in the Kaibab in the 1920s, i.e., that there are good reasons to think that a loss of predators led to a deer irruption which decreased aspen recruitment. Using the different cause-finding practices in combination can strengthen causal inferences and mitigate the shortcomings that each practice has.

The status of population genetics has become hotly debated among biologists and philosophers of biology. Many seem to view population genetics as relatively unchanged since the Modern Synthesis and have argued that subjects such as development were left out of the Synthesis. Some have called for an extended evolutionary synthesis or for recognizing the insignificance of population genetics. Yet others such as Michael Lynch have defended population genetics, declaring "nothing in evolution makes sense except in the light of population genetics" (a twist on Dobzhansky's famous slogan that "nothing in biology makes sense except in the light of evolution"). Missing from this discussion is the use of population genetics to shed light on ecology and vice versa, beginning in the 1940s and continuing until the present day. I highlight some of that history through an overview of traditions such as ecological genetics and population biology, followed by a slightly more in-depth look at a contemporary study of the endangered California Tiger Salamander. I argue that population genetics is a powerful and useful tool that continues to be used and modified, even if it isn't required for all evolutionary explanations or doesn't incorporate all the causal factors of evolution.

Recent discussions in the philosophy of biology have brought into question some fundamental assumptions regarding evolutionary processes, natural selection in particular. Some authors argue that natural selection is nothing but a population-level, statistical consequence of lower-level events (Matthen and Ariew [2002]; Walsh et al. [2002]). On this view, natural selection itself does not involve forces. Other authors reject this purely statistical, population-level account for an individual-level, causal account of natural selection (Bouchard and Rosenberg [2004]). I argue that each of these positions is right in one way, but wrong in another; natural selection indeed takes place at the level of populations, but it is a causal process nonetheless.

When philosophers of physics explore the nature of chance, they usually look to quantum mechanics. When philosophers of biology explore the nature of chance, they usually look to microevolutionary phenomena, such as mutation or random drift. What has been largely overlooked is the role of chance in macroevolution. The stochastic models of paleobiology employ conceptions of chance that are similar to those at the microevolutionary level, yet different from the conceptions of chance often associated with quantum mechanics and Laplacean determinism.

I argue that the propensity interpretation of fitness, properly understood, not only solves the explanatory circularity problem and the mismatch problem, but can also withstand the Pandora’s box full of problems that have been thrown at it. Fitness is the propensity (i.e., probabilistic ability, based on heritable physical traits) for organisms or types of organisms to survive and reproduce in particular environments and in particular populations for a specified number of generations; if greater than one generation, “reproduction” includes descendants of descendants. Fitness values can be described in terms of distributions of propensities to produce varying number of offspring and can be modeled for any number of generations using computer simulations, thus providing both predictive power and a means for comparing the fitness of different phenotypes. Fitness is a causal concept, most notably at the population level, where fitness differences are causally responsible for differences in reproductive success. Relative fitness is ultimately what matters for natural selection.

The “land community” (or “biotic community”) that features centrally in Aldo Leopold’s Land Ethic has typically been equated with the concept of “ecosystem.” Moreover, some have challenged this central Leopoldean concept given the multitude of meanings of the term “ecosystem” and the changes the term has undergone since Leopold’s time (see, e.g., Shrader-Frechette 1996). Even one of Leopold’s primary defenders, J. Baird Callicott, asserts that there are difficulties in identifying the boundaries of ecosystems and suggests that we recognize that their boundaries are determined by scientific questions ecologists pose (Callicott 2013). I argue that we need to rethink Leopold’s concept of land community in the following ways. First, we should recognize that Leopold’s views are not identical to those of his contemporaries (e.g., Clements, Elton), although they resemble those of some subsequent ecologists, including some of our contemporaries (e.g., O’Neill 2001, Post et al. 2007, Hastings and Gross 2012). Second, the land community concept does not map cleanly onto the concept of “ecosystem”; it also incorporates elements of the “community” concept in community ecology by emphasizing the interactions between organisms and not just the matter/energy flow of the ecosystem concept. Third, the boundary question can be illuminated by considering some of the recent literature on the nature of biological individuals (in particular, Odenbaugh 2007; Hamilton, Smith, and Haber 2009; Millstein 2009), focusing on concentrations of causal relations as determinative of the boundaries of the land community qua individual. There are challenges to be worked out, particularly when the interactions of community members do not map cleanly onto matter/energy flows, but I argue that these challenges can be resolved. The result is a defensible land community concept that is ontologically robust enough to be a locus of moral obligation while being consistent with contemporary ecological theory and practice.

In Darwin’s Sacred Cause, Adrian Desmond and James Moore contend that “Darwin would put his utmost into sexual selection because the subject intrigued him, no doubt, but also for a deeper reason: the theory vindicated his lifelong commitment to human brotherhood”. Without questioning Desmond and Moore’s evidence, I will raise some puzzles for their view. I will show that attention to the structure of Darwin’s arguments in the Descent of Man shows that they are far from straightforward. As Desmond and Moore note, Darwin seems to have intended sexual selection in non-human animals to serve as evidence for sexual selection in humans. However, Darwin’s account of sexual selection in humans was different from the canonical cases that Darwin described at great length. If explaining the origin of human races was the main reason for introducing sexual selection, and if sexual selection was a key piece of Darwin’s anti-slavery arguments, then it is puzzling why Darwin would have spent so much time discussing cases that did not really support his argument for the origin of human races, and it is also puzzling that his argument for the origin of human races would be so poor.

This paper aims to illustrate one of the primary goals of the philosophy of biology⎯namely, the examination of central concepts in biological theory and practice⎯through an analysis of the concepts of population and metapopulation in evolutionary biology and ecology. I will first provide a brief background for my analysis, followed by a characterization of my proposed concepts: the causal interactionist concepts of population and metapopulation. I will then illustrate how the concepts apply to six cases that differ in their population structure; this analysis will also serve to flesh out and defend the concepts a bit more. Finally, I will respond to some possible questions that my analysis may have raised and then conclude briefly.

Recently, a number of philosophers of biology have endorsed views about random drift that, we will argue, rest on an implicit assumption that the meaning of concepts such as drift can be understood through an examination of the mathematical models in which drift appears. They also seem to implicitly assume that ontological questions about the causality of terms appearing in the models can be gleaned from the models alone. We will question these general assumptions by showing how the same equation — the simple 2 = p2 + 2pq + q2 — can be given radically different interpretations, one of which is a physical, causal process and one of which is not. This shows that mathematical models on their own yield neither interpretations nor ontological conclusions. Instead, we argue that these issues can only be resolved by considering the phenomena that the models were originally designed to represent and the phenomena to which the models are currently applied. When one does take those factors into account, starting with the motivation for Sewall Wright’s and R.A. Fisher’s early drift models and ending with contemporary applications, a very different picture of the concept of drift emerges. On this view, drift is a term for a set of physical processes, namely, indiscriminate sampling processes

Genetic drift (variously called “random drift”, “random genetic drift”, or sometimes just “drift”) has been a source of ongoing controversy within the philosophy of biology and evolutionary biology communities, to the extent that even the question of what drift is has become controversial. There seems to be agreement that drift is a chance (or probabilistic or statistical) element within population genetics and within evolutionary biology more generally, and that the term “random” isn’t invoking indeterminism or any technical mathematical meaning, but that’s about where agreement ends. Yet genetic drift models are a staple topic in population genetics textbooks and research, with genetic drift described as one of the main factors of evolution alongside selection, mutation, and migration. Some claim that genetic drift has played a major role in evolution (particularly molecular evolution), while others claim it to be minor. This article examines these and other controversies. In order to break through the logjam of competing definitions of drift, this entry begins with a brief history of the concept, before examining various philosophical claims about the proper characterization of drift and whether it can be distinguished from natural selection; the relation of drift to debates over statisticalism; whether drift can be detected empirically and if so, how; and the proper understanding of drift as a model and as a (purported) law.

Biologists studying ecology and evolution use the term “population” in many different ways. Yet little philosophical analysis of the concept has been done, either by biologists or philosophers, in contrast to the voluminous literature on the concept of “species.” This is in spite of the fact that “population” is arguably a far more central concept in ecological and evolutionary studies than “species” is. The fact that such a central concept has been employed in so many different ways is potentially problematic for the reason that inconsistent usages (especially when the usage has not been made explicit) might lead to false controversies in which disputants are simply talking past one another. However, the inconsistent usages are not the only, or even the most important reason to examine the concept. If any set of organisms is legitimately called a “population,” selection and drift processes become purely arbitrary, too. Moreover, key ecological variables, such as abundance and distribution, depend on a nonarbitrary way of identifying populations. I sketch the beginnings of a population concept, drawing inspiration from the Ghiselin-Hull individuality thesis, and show why some alternative approaches are nonstarters.

Recent work on the heat-shock protein Hsp90 by Rutherford and Lindquist (1998) has been included among the pieces of evidence taken to show the essential role of developmental processes in evolution; Hsp90 acts as a buffer against phenotypic variation, allowing genotypic variation to build. When the buffering capacity of Hsp90 is altered (e.g., in nature, by mutation or environmental stress), the genetic variation is "revealed," manifesting itself as phenotypic variation. This phenomenon raises questions about the genetic variation before and after what I will call a "revelation event": Is it neutral, nearly neutral, or non-neutral (i.e., strongly deleterious or strongly advantageous)? Moreover, what kinds of evolutionary processes do we take to be at work? Rutherford and Lindquist (1998) focus on the implications of non-neutral variation and selection. Later work by Queitsch, Sangster, and Lindquist (2002) and Sangster, Lindquist, and Queitsch (2004) raises the possibility that Hsp90 buffering may play the role that was played by drift in Sewall Wright's shifting balance model, permitting transition from one adaptive peak to another. However, Ohta (2002) suggests that much of this variation may be nearly neutral, which in turn, would imply a strong role for drift as well as selection. The primary goal of this paper is to illuminate the alternative scenarios and the processes operating in each. At the end, I raise the possibility of a synthesis between evo-devo and nearly neutral evolution.