The notion of plasticity, most commonly understood as the ability of organisms to modify their characteristics in response to environmental conditions during lifetime, occupies an important place in the theory and practice of biology. Its centrality as a conceptual tool for analysing living systems has garnered attention from philosophers and historians of science. ^[1] Antonine Nicoglou’s Plasticity in the Life Sciences is the latest book-length contribution to these interdisciplinary conversations. It traces the evolution of the idea (or, more accurately, ideas) of plasticity within Western philosophical and scientific thought, with special attention to the role these have played in the more recent debates concerning development and evolutionary change. In doing so, the book not only provides an exceptionally rich historical account of plasticity but also touches upon a number of problems that animate present-day philosophy of biology.

Early on, Nicoglou raises some broader questions about the central concept, of which perhaps the most important one concerns its scientific value. As she puts it:

Is the use of this term just a way of marveling at the diversity of living forms? Or is it a way of characterizing a set of phenomena that, if not always as spectacular as in the cases described, are nevertheless general and constant in the life sciences? Is plasticity a cloak used to hide the biologist’s ignorance, or is it a scientific concept used to describe an original and specific characteristic of how living organisms interact with the environment in which they live? (p. 3)

This passage introduces the main critical theme of the book: can the ubiquitous but often loose talk of plasticity in the life sciences be associated with any tangible epistemic benefits, such as providing a name for a specific type of natural phenomena or bridging different research programmes that study how organisms interact with their environments? In other words, can the notion of plasticity earn its keep, despite its frequent elusiveness and resistance to precise definition? The author sets out to address these questions in two steps. First, she shows that at least two different ways of understanding plasticity (she labels them as ‘active’ and ‘passive’) have existed alongside or superseded one another over the centuries. Then, she examines how this ambivalence manifests in the contemporary research practices of biologists, resulting in conceptual confusion but also providing a link between different lines of investigation. By framing the book in this way—as an inquiry into the past and present uses of an important but potentially troublesome category—Nicoglou aligns it not only with the tradition of intellectual history but also with the work in history and philosophy of science that centres on polysemous concepts in biology. ^[2]

Part 1 (chapters 1–5) of the book offers a genealogical account of the plasticity concept—including, but not limited to, its historical recurrence within natural philosophy. In this context, Nicoglou suggests, plasticity has often been envisioned as an active force behind the unfolding of living structures throughout development. As she highlights in chapter 1, such a perspective was present in Aristotle’s writing on generation as well as in the work by later European metaphysicians (such as Christian Wolff), whose ideas can be seen as a precursor to embryology. It is no surprise, then, that the active sense of plasticity also came to inform embryological investigations (and later developmental biology which has an important, if complex, ^[3] historical connection with embryology). Yet, according to the author, a more ‘passive’ sense of the concept can also be identified in many philosophical attempts to understand life. It conveys a propensity to assume different forms in response to environmental influence, redirecting attention from the processes of development to the outcomes of those processes and the resulting variety of biological forms. This view of plasticity similarly goes back to Ancient philosophy and has often been invoked alongside its active counterpart. However, Nicoglou notes that, beginning in the nineteenth century, the passive meaning begins to get more traction, which sets the stage for its later dominance within the twentieth-century life sciences.

Chapter 3 turns to these more recent scientific contexts by outlining the intellectual trajectory of the norm of reaction concept, first introduced by Richard Woltereck and later taken up by British and US geneticists. Drawing on work by Sarkar (1999), Nicoglou suggests that while Woltereck himself had a more processual (‘phenogenesis’) and non-reductionist interpretation of the Reaktionsnorm, thus relying on an active meaning of plasticity, it was subsequently reinterpreted in a more gene-centric and passive way, as an inherent tendency of a genotype to be expressed differently in response to environmental cues. This conceptual shift, according to the author, accompanied broader changes in the organization of the biological discipline, with genetics acquiring the central status it still enjoys today. There is some tension in how the book characterizes these developments corresponding to the crystallization of the modern synthesis (chapters 4 and 5). On the one hand, in the wake of the synthesis, the concept of plasticity finally received a specific, technical definition as the ability of a genotype to give rise to distinct phenotypes in different environmental conditions. This is the interpretation of phenotypic plasticity that was provided by Bradshaw (1965) and became influential in biology (and, by extension, philosophy of biology). On the other hand, as Nicoglou seems to suggest, operationalizing plasticity in this way unduly restricted the scope of discussion to its potential evolutionary explanations (treating it as an evolved trait in its own right), rather than investigating its developmental sources, thereby asserting the primacy of the passive dimension of the concept. Importantly, these points highlight that for the author of the book, the active meaning of plasticity—particularly as used in the more contemporary debates—pertains mainly to the study of development, whereas the passive one is associated with a focus on phenotypic variation. When understood in this way, the dichotomy acquires an affinity with other distinctions previously used in philosophy of biology. For example, Tabery’s (2014) work on gene–environment interaction (a topic closely linked to the study of phenotypic plasticity) centres on two divergent approaches: elucidating developmental mechanisms and partitioning trait variance with statistical methods.  This suggests that such dichotomies capture an important and recurrent feature of twentieth and twenty-first century debates about how organismal responses to environmental factors ought to be conceptualized and investigated.

In part 2 (chapters 6–10), Nicoglou discusses the different roles plasticity concepts can play when biologists seek to explain living phenomena. Here, she argues that plasticity can be invoked either as a developmental explanans of variation or as an explanandum of evolutionary theory. Chapters 6 and 7 examine the first possibility by analysing how biologists study embryonic induction and biological regulation, and what the explanatory payoff of invoking plasticity might be in this context. The author begins this examination with an overview of several prominent accounts of scientific explanation so as to place her reflections on a more general philosophical footing. She then suggests that references to plasticity can be illuminating in the context of studying inductive and regulatory phenomena, although she concedes that one would need to provide some causal mechanistic detail regarding the underlying processes in order to achieve genuine explanatory power. The types of epistemic benefits the concept of plasticity can offer, then, are not explanatory in a strict sense (although this point is not stated very clearly in the book), but are better understood as heuristic or descriptive. Plasticity serves as a loose conceptual connection (‘boundary concept’, to use Nicoglou’s term of choice) between different mechanistic explanations, prompts further investigative efforts if such explanations are incomplete, and picks out a distinctive (if multiply realizable) biological phenomenon.

Chapter 8 investigates what happens when plasticity itself becomes an object of explanation. A question of particular interest is what kind of an explanation is most relevant in this case—for instance, whether plastic phenomena should be explained by reference to natural selection or if they are better elucidated in ontogenetic terms. The author draws on debates in philosophy of biology concerning the explanatory role of selection to suggest that both ways of explaining plasticity can be appropriate and, in fact, may be needed, depending on the exact question being asked. While natural selection may explain the distribution of plasticity as a characteristic in a population, it does not necessarily shed light on its developmental basis. Because of this, Nicoglou calls for explanatory pluralism and even gestures toward an eventual integration of explanations—not just in the context of plasticity but also in the context of phenomena like canalization, which may be thought of as the diametric opposite of a plastic response.

However, the very next chapter (chapter 9) tempers any optimism regarding the prospects for such integration more generally. This chapter centres on the innovative work in biology that is meant to bring together developmental and evolutionary perspectives and in which the notion of plasticity plays an important role. More specifically, the discussion focuses on developmental systems theory (DST) and the extended evolutionary synthesis (EES).  Here, Nicoglou paints a picture of disunity: as she claims, plasticity is studied at different scales and levels of analysis, generating local insights but ultimately making integration difficult. Moreover, she wonders whether the relevant research programmes have managed to supplant the genotype-focused notion of phenotypic plasticity with an equally well-defined concept of their own. Taken together, these remarks make the author’s position appear somewhat conflicted. It would seem that she regards both the proliferation of diverse plasticity concepts and the entrenchment of a single concept as problematic, yet it remains unclear where, in her view, the appropriate balance between these two extremes lies.

Where does this all leave us with regard to the main problem highlighted at the beginning: the epistemic utility of the notion of plasticity for scientific practice? After meticulously scrutinizing and contextualizing various uses of plasticity throughout the book, Nicoglou finally settles on a surprisingly broad and abstract appraisal of the concept’s future theoretical role. At the end of chapter 10, she suggests that the idea of plasticity may function merely as a ‘facsimile of naturalness’ (p. 255)—a distinctive and widespread feature of life whose more substantive content remains open-ended. One might worry that this does not provide a very specific or informative answer to the overarching questions about plasticity posed earlier in the book, especially since there are many other plausible candidates (for instance, variability or growth) that fit the ‘facsimile of naturalness’ designation at least equally well. However, whether or not a reader finds these final remarks satisfactory, the questions themselves are still very much worth raising and reflecting on, both by philosophers and by scientists whose practice is informed by the relevant conceptual frameworks. This is what the book does rather successfully—instead of taking the idea of plasticity for granted (as is often the case), it puts it at the centre of a problem agenda other critically minded researchers will undoubtedly want to engage with and build upon.

Overall, Plasticity in the Life Sciences offers a highly relevant and detailed account of plasticity in biology that will be of interest to audiences in philosophy of science, among others. Although many readers will likely find themselves challenged by the richness and complexity of the book’s content, it is also these qualities of Nicoglou’s work that make the reading experience rewarding.

Olesya Bondarenko
Konrad Lorenz Institute for Evolution and Cognition Research
olesya.bondarenko@kli.ac.at

Notes

¹ See, for example, (Pigliucci 2001; Rees 2016; Meloni 2019).

² See, for example, (Löwy 1992; Ereshefsky 1998; Griffiths and Neumann-Held 1999; Fox Keller 2000, 2010; Stotz et al. 2004; Clarke 2010; Brigandt and Love 2012; Neto 2020; Bocchi 2024).

³ See (Hopwood 2019).

References

Bocchi, F. (2024). ‘Biodiversity Skepticism and Measurement Practices’, Biology and Philosophy, 39, available at doi.org/10.1007/s10539-024-09973-x.

Bradshaw, A. D. (1965). ‘Evolutionary Significance of Phenotypic Plasticity in Plants’, Advances in Genetics, 13, pp. 115–55.

Brigandt, I. and Love, A. C. (2012). ‘Conceptualizing Evolutionary Novelty: Moving Beyond Definitional Debates’, Journal of Experimental Zoology B, 318, pp. 417–27.

Clarke, E. (2010). ‘The Problem of Biological Individuality’, Biological Theory, 5, pp. 312–25.

Ereshefsky, M. (1998). ‘Species Pluralism and Anti-realism’, Philosophy of Science, 65, pp. 103–20.

Fox Keller, E. (2000). The Century of the Gene, Harvard University Press.

Fox Keller, E. (2010). The Mirage of a Space Between Nature and Nurture, Duke University Press.

Griffiths, P. E. and Neumann-Held, E. M. (1999). ‘The Many Faces of the Gene’, BioScience, 49, pp. 656–62.

Hopwood, N. (2019). ‘Inclusion and Exclusion in the History of Developmental Biology’, Development, 146, available at doi.org/10.1242/dev.175448.

Löwy, I. (1992). ‘The Strength of Loose Concepts: Boundary Concepts, Federative Experimental Strategies, and Disciplinary Growth: The Case of Immunology’, History of Science, 30, pp. 371–96.

Meloni, M. (2019). Impressionable Biologies: From the Archaeology of Plasticity to the Sociology of Epigenetics, Routledge.

Neto, C. (2020). ‘When Imprecision Is a Good Thing, or How Imprecise Concepts Facilitate Integration in Biology’, Biology and Philosophy, 35, available at doi.org/10.1007/s10539-020-09774-y.

Pigliucci, M. (2001). Phenotypic Plasticity: Beyond Nature and Nurture, Johns Hopkins University Press.

Rees, T. (2016). Plastic Reason: An Anthropology of Brain Science in Embryogenetic Terms, University of California Press.

Sarkar, S. (1999). ‘From the Reaktionsnorm to the Adaptive Norm: The Norm of Reaction, 1909–1960’, Biology and Philosophy, 14, pp. 235–52.

Stotz, K., Griffiths, P. E. and Knight, R. (2004). ‘How Biologists Conceptualize Genes: An Empirical Study’, Studies in History and Philosophy of Biological and Biomedical Sciences, 35, pp. 647–73.

Tabery, J. (2014). Beyond Versus: The Struggle to Understand the Interaction of Nature and Nurture, MIT Press.