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Biological Individuality
Integrating Scientific, Philosophical, and Historical Perspectives
By Scott Lidgard, Lynn K. Nyhart The University of Chicago Press
Copyright © 2017 The University of Chicago
All rights reserved.
ISBN: 978-0-226-44645-5
CHAPTER 1
The Work of Biological Individuality: Concepts and Contexts
SCOTT LIDGARD AND LYNN K. NYHART
The whole question seems to turn upon the meaning of the word "individual."
THOMAS HENRY HUXLEY (1852, 185)
There is, indeed, as already implied, no definition of individuality that is unobjectionable.
HERBERT SPENCER (1864, 206)
Between them, Huxley and Spencer got it right. Individuality is a basic concept in biology, yet there is no broad agreement on its meaning. Not unlike other wide-ranging concepts, biological individuality is a nomadic chameleon, "subject to constant reification and change while crossing and turning across disciplines and non-scientific domains" (Surman et al. 2014, 127). Not only biologists, but also historians and philosophers of biology adopt and reanalyze the concept. Why is it so difficult to isolate a meaning for biological individuality, yet so useful to biologists that they continually put different versions of an individuality concept to work?
Put to work on specific biological problems, individuality concepts provide structure and buttress generality, predictability, and explanatory power — though seldom all together (J. Wilson 1999). They do their work in the contexts of biologists' questions and epistemic practices, in a historically contingent yet continually changing landscape of biological knowledge and theoretical interpretation, and in philosophical views biologists draw upon. We suggest that biologists, historians, and philosophers need to appreciate all of these. In this chapter, we first show that a broad spectrum of definitional criteria of individuality has been integral to biological studies for at least 170 years. We then argue that this work is necessarily contextualized by specific problems, and lay out the notion of a problem space as a way to think about such contextualization and the place of individuality concepts within it. Our next section shows how many (if not most) specific problems concerning individuality can be seen as distributed across four stable and continuous kinds of problems: individuation, hierarchy, temporality, and constitution. We then briefly consider individuality from perspectives of relationality and interaction — systems, networks, and processes. In closing, we advocate a rethinking of what biological individuality concepts are meant to do in biology. Rather than arguing over whether this or that specific concept and definitional criterion is right or best, a more promising way forward is to recast biological individuality as a broad, stable domain of problems, a "problem agenda" (Love 2014, forthcoming).
Definitions and Criteria of Biological Individuality
There is now a sprawling definitional diversity of biological individuality concepts, constituted by dozens of old and new criteria defining "individual" or its contained subset "organism." These definitions and criteria don't always agree in picking out the same biological objects (Clarke 2010), and perhaps agree even less when some of their theory-driven underpinnings are compared. This section presents some of the definitional criteria that have been proposed for either biological "individuals" or "organisms" (Table 1.1), before moving on to the four kinds of problems we introduced earlier. Our compilation includes some 146 publications from 1800 to the present that have offered definitions or criteria for either one or both of these terms. While the terms are not equivalent, they have been used interchangeably in many publications, precluding a simple separation here. We have attempted to parse the references into groups by approximate criteria in order to facilitate comparisons.
It is important to recognize that a number of these criteria overlap, and that a reference may endorse a definition using either a single criterion or several. Also, many definitional criteria allow for degrees of individuality and degrees of organismality (Verworn 1899; Bergson 1911; Conklin 1916; J. Huxley 1926, 1949; Sober 1991; Godfrey-Smith 2009; Queller and Strassmann 2009; Strassmann and Queller 2010; Herron et al. 2013; Wolfe 2014), although some references don't endorse this view. A few authors have combined multiple criteria into higher definitional categories or factors that abstract away from some of the more material criteria in Table 1.1. For instance, the criterion of high cooperation and low conflict could be considered to subsume germ-soma separation, policing, and bottlenecks (Herron et al. 2013). Godfrey-Smith (2011) discusses two categories that may overlap in different senses of individuality, "Darwinian individuals" and (in a non-Darwinian sense) organisms. Clarke (2012) subsumes a range of different criteria within each of two factors, one that ensures variation among biological objects in a population and another that acts to constrain variation within each object. These factors attempt to combine the effects of certain other criteria listed in Table 1.1 that could influence heritable variation in fitness, her overriding concern. Goodnight (2013) offers three definitions of individuality in terms of fitness, with an informed discussion of models, criteria, or fitness proxies that could actualize them: units of fitness at a chosen organizational level, objects at the lowest level experiencing natural selection, and objects at the lowest level displaying an evolutionary response to natural selection. He states clearly that it is the observer who imposes an abstract concept of individuality. This is hardly a new observation: "in general the concept of individual being, in the various special sciences, as well as in inquiry, shows many characters that cannot be derived from mere perception in any case" (Royce 1901, 535) Yet these sorts of abstractions, some with strong theoretical underpinnings, may lead to an epistemological or decidedly empirical question when framed in terms of the practice of biologists. What sorts of assumptions or observations or workflows are needed to actualize a given criterion? This last question has garnered far too little attention.
Numerous comparative accounts of biological individuality and organism concepts exist as narratives, surveys, or compilations of definitional criteria (Geddes and Mitchell 1911; Mumford 1925; Bell 1982; Hull 1992; Keller and Ewing 1993; J. Wilson 1999; de Sousa 2005; R. Wilson 2005; Clarke 2010; Strassmann and Queller 2010; Boulter 2013; Herron et al. 2013; Wilson and Barker 2013). Neither our compilation nor any one of these are necessarily the "right" one, all the more so as criteria often remain implicit in definitions. Thus the criteria as we have specified them are heuristic approximations. They might be stated or grouped differently by another worker, and certain references might be reassigned relative to the arrangement in Table 1.1. Lastly, while our compilation is more comprehensive than others, it is hardly complete. A fuller exploration would undoubtedly add more references for various criteria, and extend some criteria further back in history.
Setting all these provisos aside for the moment, what can we say about "individuality" and "organism"? Figure 1.1 shows definitional criteria of "biological individuals" or "organisms" in historical view. It confirms that they have been topics of research in biology continuously for at least 170 years and possibly more. Criteria of propagation and life cycles, and of causal integration of biological objects as individuals or organisms, have held steadfast. Similarly, the criterion of comprising or being part of a biological hierarchy has a history showing the persistence of "individuality at different organizational levels." Looking more closely at the substance of publications in Table 1.1 reveals that individuality of species, solitary and modular organisms, and cells all received attention in the nineteenth century. So too did problems that involved continuity and change over time, from reproduction and life cycles to evolutionary lineages. Soon after, chromosomes, genes, immunological units, developmental modules, and symbiotic entities garnered attention. Near the end of the twentieth century through today, more abstract criteria related to Darwinian evolution, especially selection and theoretical fitness, assumed a central role. We suggest that this last pattern has drawn from what Gould (1983) termed the hardening of the modern synthesis, from units of selection (Lewontin 1970) and subsequent multilevel selection theory (Okasha 2006), and from the evolution of individuality (Buss 1987) and major evolutionary transitions (Maynard Smith and Szathmáry 1995). Yet despite the brash prominence of these newer criteria, they have not replaced their predecessors in the discourse over biological individuality — far from it. Many earlier criteria and problems of biological individuality in philosophy and science did not lose their meaning, significance, or influence with the invention and diversification of their most recent counterparts. (Individuality criteria that are no longer used at all, such as those reflecting extreme goal-directedness or divine providence, have been omitted here.) The enduring character of definitional criteria as an assemblage becomes even more apparent as we turn to situating biological individuality concepts within different problem-contexts. We begin by considering the nature of those problem-contexts.
Concepts — Moving through Changing Problem Spaces and across Contexts
Historians, philosophers, and biologists interested in biological individuality share certain crucial areas of concern. The largest and most obvious are matters of epistemology and scientific theory, and involve concepts of biological individuality. Concepts perform a wide variety of work in biological problem-solving and theorizing (Brandon 1996; Hall and Olson 2007; Schwarz 2011; Feest and Steinle 2012a). We argue here that the work of biological individuality concepts has to be understood contextually. While "context" can be taken at many levels, here we are most concerned with the roles of individuality concepts in the relation to biologists' immediate activities: forming problems within a given domain, classifying, reasoning, investigating, experimenting, modeling, explaining, and communicating (Feest and Steinle 2012b; Sterner 2015).
We focus on three senses of contextuality, without excluding the prospect of others. The first is the practice-driven approach of biologists themselves, involving the interaction of concepts and problem spaces (e.g., Bechtel 1984; Brigandt and Love 2012). Here it may be useful to have a model to think with. Allen Newell and Herbert Simon (1972) devised the notion of a "problem space" in which a problem solver, say a biologist, confronts a specific problem or task and determines a task environment in terms of an initial problem state (Fig. 1.2). This environment supplies but is not limited to a breadth of information about the specific system under consideration, associated knowledge, and theory. The problem space within it is constrained by the problem-solver by selecting certain relevant information in the task environment, the state of the problem in its initial form, alternate or intermediate problem states considered along the way toward the goal state, and the goal or solution state. The problem space itself changes as the problem is studied, as information and alternate problem states are investigated. As originally proposed, its multiple dimensions are explored mathematically and algorithmically in attempting a solution. A key insight is that "a great many of the characteristics of the problem solving systems ... can be inferred, at least in broad outline, from the structure of the environments in which they operate. ... The forms this information takes condition the possible modes of its exploitation" (Newell and Simon 1972, 834). In other words, the problem context conditions the terms for solving the problem. Kovaka (2015) defends a roughly similar claim of contextuality with respect to biological individuality and scientific practice.
Here we step away from Newell and Simon's precise mathematical statement. Instead, we use a less formal dynamic problem space in which preexisting as well as newly developing concepts can move through permeable boundaries, and historical, social, and philosophical facets are also present. For any problem-solver, each distinct problem has its own problem space (cf. Nersessian 2006; Love 2014, 2015a, forthcoming). Consider a solving process that begins with a scientific problem involving biological individuality, one that needs to individuate the entities under consideration, whether in a physiological, ecological, evolutionary, or other area (designated by the full interior of Figure 1.2). A biologist's initial problem helps circumscribe a task environment. Individuation of key entities can draw on one or more existing (or new) individuality concepts and definitional criteria, which are contextualized by their reference to the specific problem and its system. A problem involving the individuality of a consumed organism converted metabolically in its consumer (Landecker, this volume) calls for an individuality concept that will classify entities differently from a problem involving evolutionary transitions to multicellularity in green algae (Herron, this volume). The two problems will also support radically different explanatory inferences.
While biological individuality concepts can perform work in a classificatory role (identifying kinds of individuals or criteria of individuality), they can also do so in explanatory or other roles. Thus, the "epistemic goal" of a research problem (Brigandt 2010a, 2012) is another potentially important part of a concept's work. Is the problem more empirical or theoretical? Is it synchronic, in a short moment, or diachronic, extending over time? Is it on one level of a biological hierarchy or many? Does it focus on pattern or process, structure or function? These and other sorts of questions reflect epistemic goals that shape the problem space and further contextualize the work done by a given individuality concept (or organism concept [Wolfe 2014]). A concept may work in a distinctly explanatory role as our biologist works through her problem space toward a solution; it may be part of the goal or even the goal state itself. For example, concepts that frame biological individuals principally or entirely in terms of natural selection or fitness are often used in explanatory roles in the study of major evolutionary transitions. Yet these concepts may bracket off material or structural elements that are needed for a fuller understanding, and might necessarily employ a broader or complementary concept of biological individuality (Sterner, this volume; Love and Brigandt, this volume). Also, many problems are initially "ill-structured" (Simon 1973), resulting in modification of the problem space, drawing new information from the task environment or externally (Fig. 1.2). Here again, the concepts can change with a revised context.
A second sense of the contextuality of biological individuality concepts exposes the different perspectives that biologists, philosophers, and historians bring to the table. The schema for our biologist (Fig. 1.2) could apply as well for a historian or a philosopher, but the concepts and problem space would differ for their specific problems, reflecting what they consider germane to their task environments. An experimental developmental biologist analyzing functional integration, for example, might organize a problem space largely in terms of structural objects, spatial boundaries, and morphogenetic interactions to individuate molecular or morphological objects and understand changes during ontogeny. A philosopher studying the same system from an evolutionary viewpoint might organize a problem space to develop an axiomatic or otherwise formal account of individuality, relying on a "fundamental" theory of natural selection and functional properties. While the two contextual perspectives may indeed individuate the same objects, the structural properties approach of the developmental biologist is not generally directed by fundamental philosophical theory (Love forthcoming).
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Excerpted from Biological Individuality by Scott Lidgard, Lynn K. Nyhart. Copyright © 2017 The University of Chicago. Excerpted by permission of The University of Chicago Press.
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