During the last decades the question of defining life has gained increased interest but, at the same time, the difficulty in reaching consensus on a possible answer has led many to skeptical positions. This, in turn, has raised a wider debate about why defining life is so hard and controversial. Such a debate (or ‘meta-debate’) introduces additional aspects to be considered, like the role and nature of a definition of life itself. In this paper, we will focus on those aspects, arguing that progress can be made (and has, indeed, been made) if we conceive definitions of life as open heuristic tools that contribute(d) to develop specific research strategies in the biological sciences and, more generally, to increase our understanding of life’s complexity. In contrast with pragmatic or operationalist approaches, we will defend that definitions of life comprise a set of ontological assumptions, together with an inherent unifying vocation, so they should be subject to comparison and critical assessment, closely related to the success or failure of the corresponding research programs, but also to the success or failure in establishing well-grounded interconnections among the latter. We consider that the search for a more coherent, integrated and generalized theory of biology cannot be pursued without keeping an empirical standpoint, and the exercise of defining life should not be taken as an obstacle but as a valuable (and, of course, evaluable) instrument to achieve that goal.
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According to the Cambridge Dictionary a definition is a description of the features and limits of something, trying to specify the criteria through which we can uniquely identify it. Cleland and Chyba (2002), following another entry of the same dictionary (Audi 1995), go further and state that a definition, in a logician’s sense, should specify necessary and sufficient conditions for the application of the term being defined. Anyhow, it is clear that definitions are more demanding than conceptions (which could remain rather vague or implicit), precisely because they are attempts to make those characteristic aspects/features of a phenomenon as apparent and clear as possible, avoiding circularities, overlaps, etc. For a more thorough account about the requisites that definitions of life, in particular, should meet, see: (Emmeche 1998; Ruiz-Mirazo et al. 2004).
For the purpose of our argument, we do not need to endorse here all the ingredients of the Lakatosian theory of science. For instance, we do not consider that all scientists in a particular research program should share all the claims of the corresponding ‘hard core’ (instead, they could sometimes disagree on certain aspects, like Robert Richards (1987) correctly pointed out). Similarly, we do not subscribe the way in which Lakatos explains the “progressivity” of a research program (Laudan 1977).
This, of course, is the result of a historical process (which could be termed as the “pre-history” of a given scientific discipline) during which that community becomes constituted. Most historians of biology agree that the birth of this discipline could be dated back to, approximately, 1800.
There are some similarities between the process described here and what Hasok Chang calls ‘epistemic iteration’, i.e., a process « in which successive stages of knowledge, each building on the preceding one, are created in order to enhance the achievement of certain epistemic goals » (Chang 2004, p. 45), and where a succession of approximations, corrections, changes and revisions during this process increases the degree of accuracy, explanatory power, consistency (and other epistemic values) of scientific outcomes and knowledge.
For instance, the community of computational ‘a-lifers’ (Langton 1989, 1992; Boden 1996) failed in this regard. They posed a number of very interesting questions for biology, but they did not manage to include their domain of research into that of the standard life sciences. Basically, most biologists did not accept as common to them the new empirical referents that ‘a-lifers’ introduced for their research.
A similar view is defended by Tirard et al. (2010) when they say that « research in the origin and nature of life is doomed to remain, at best, as a work in progress. It is difficult to find a definition of life accepted by all, but the history of biology has shown that some efforts are much more fruitful than others » (p. 1008). See also (Smith 2016).
This is not to say that the quest for definitions of life should not be guided by the goal to find, so to speak, successful definitions -- by which we mean meta-stable points in this dynamic scenario. To express it in simple terms, we could use the motto: ‘revise data, given explanation; revise explanation, given data; until some (transient) equilibrium is reached’ (which includes definitions, why shouldn’t it?).
For instance, those between mechanicists and organicists; between physiology-centered and evolutionary-centered research programs; between analytic and integrative strategies…. We should remark here that our use of the term ‘paradigmatic’ is not in a strict Kuhnian sense: it does not imply the incommensurability of different scientific research programs, organized around a central conceptual core, but just conveys the idea that we can indirectly evaluate and compare this conceptual core—and even make progress towards the integration between different research programs and outcomes, as we have argued.
Bare lists of properties, for instance, have not proved fruitful over the years, so they should be regarded with skepticism, if not utterly discarded (Ruiz-Mirazo et al 2004). Among other problems, they do not provide a suitable platform to elaborate an explanatory account around them, like any definition of life should do—showing (with as much precision and clarity as possible) how the different concepts, properties and processes involved relate to each other. Recent arguments in favor of interpreting life as a ‘homeostatic property cluster kind’ (‘HPC-kind’, as opposed to traditional notion of ‘natural kind’ (Diéguez 2013; Ferreira and Umerez 2018)) do not overcome this severe difficulty of ‘list definitions’, in our view.
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All authors acknowledge support from two research projects, one from the Basque Government (IT 1228-19), and one from MINECO (FFI2014-52173-P). AM also held the Salvador de Madariaga Fellowship PRX17/00379, and would like to thank the IHPST (Paris) for hosting his research stay during the first semester of 2018. KR-M got support from the European Commission (Marie Curie ITN Program: ‘ProtoMet’—Grant Agreement no. 813873—Horizon 2020) and was part of COST Action TD 1308 (‘Origins and evolution of life on Earth and in the Universe’) during the elaboration of this article. Leonardo Bich’s careful reading and valuable comments on a previous manuscript are also highly appreciated.
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Amilburu, A., Moreno, Á. & Ruiz-Mirazo, K. Definitions of life as epistemic tools that reflect and foster the advance of biological knowledge. Synthese (2020). https://doi.org/10.1007/s11229-020-02736-7
- Definition of life
- History and philosophy of biology
- Theoretical biology
- Research programs
- Epistemic controls
- Conceptual integration
- Unifying power