Abstract
The philosophy of biology is witnessing an increasing enthusiasm for what can be called “individuals thinking”. Individuals thinking is a perspective on the metaphysics of biological entities according to which conceiving of them as individuals rather than kinds enables us to expose ongoing metaphysical debates as focusing on the wrong question, and to achieve better accounts of the metaphysics of biological entities. In this paper, I examine two cases of individuals thinking, the claim that species are individuals and the claim that life on Earth is an individual. I argue that these claims fail to do the metaphysical work that one would want them to do. I highlight problems with the specific claims as well as with the general notion of ‘individual’, and argue that naturalistic metaphysicians of biology should think of the metaphysical status of theoretical entities, such as species and life, as fundamentally theory-dependent. This implies a metaphysical pluralism, that allows that in some theories species, life, and other such entities may feature as individuals, whereas in others they may feature as kinds.
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Notes
There is a difference between the cases of ‘species’ and ‘gene’ on the one hand and the case of ‘life’ on the other, which I highlight here to avoid possible confusion. In both the cases of ‘species’ and ‘gene’ there are many scientific terms that are thought of as kind terms. When thinking about ‘species’ or ‘gene’ as kind terms, authors talk about those terms as kind terms: ‘species’ as referring to the kind of which D. melanogaster and E. coli are members, and ‘gene’ as the kind of which PAX6 and dachshund are members. But they are primarily talking about D. melanogaster, E. coli, PAX6, dachshund, and so on as kinds of which individual organisms and DNA segments are members. The proposal that species or genes are individuals pertains to the latter kinds (the named species and named gene kinds), but not the former – that is, not to the species category and the gene category themselves (see also Reydon, 2009). For the case of life, however, authors consider ‘life’ as a kind term with individual living beings as its members. There is no layered conceptual structure (paralleling the cases of ‘species’ and ‘gene’) of life as a category of kinds that in turn have individual living beings as their members. So, the cases are different (which is why I address the ‘species’ and ‘life’ cases separately). Note, though, that by distinguishing between life-as-a-kind and life-as-an-individual, Hermida (2016) and Mariscal and Doolittle (2018) in fact introduce such a conceptual structure: for them, life might be thought of as a kind or category of which life on Earth (as an individual) is the only known member. In contrast to Hermida, Mariscal and Doolittle are quite skeptical about ‘life’ as a kind term. The case of life will be discussed in Sect. 3, but some clarification of this matter was necessary at this point.
I will not discuss Rosenberg’s solution to the “gene problem”, as I have already criticized this case elsewhere (Reydon 2009).
The naturalism I endorse says that metaphysicians must defer to science when it comes to asking what our world is like, as scientific investigation provides our best access to the world. The project of naturalistic metaphysics (or metaphysics of science), then, is to elucidate the natures of the “things” – material objects, kinds, events, processes, and so on – that our best scientific theories talk about.
Some authors have avoided this problem by denying that there is anything in common between species and thus denying the reality of the species category (Ereshefsky 1992, 2010, 2011). This view involves realism about the referents of binomial species names, but anti-realism about the species category. I endorse this approach to the species problem.
I will not be concerned here with the folk concept of life and thus skip Machery’s arguments on this matter.
Work on the problem includes Luisi (1998), Sterelny and Griffiths (1999: Chapter 15), Cleland and Chyba (2002), Koshland (2002), Ruiz-Mirazo et al. (2004, 2010), Dupré and O’Malley (2009), Forterre (2010), Macklem and Seely (2010), Morange (2010), Cleland (2012), Cleland and Zerella (2013), and Smith (2016, 2018).
This latest common ancestor of all life may have been a single cell, a population or a species (see Mariscal and Doolittle, 2018, pp. 7–8). Note that while Hermida uses ‘life’, Mariscal and Doolittle insist on using the capitalized proper name ‘Life’ to distinguish life on Earth (as an individual) from the possible kind.
A fourth count might be that the claim that there is no category of life is the simplest hypothesis and therefore should be taken as the null hypothesis is in need of elaboration. For one, Mariscal and Doolittle fail to explain what they mean by the simplicity of a hypothesis. Involved as a hidden premise in their argument is Occam’s Razor (Doolittle, personal correspondence). But the problem here is that, while for scientific hypotheses Occam’s Razor generally works well, for metaphysical hypotheses is doesn’t always work. In the case under consideration, if we assume that life on Earth (‘Life’ in Mariscal and Doolittle’s terms is an individual) and we assume that there is no category of life that Life is a member of, we end up with an individual that is not of any kind (as long as no other kind of entities has been identified to which Life belongs). On some metaphysical systems that might be unproblematic, but certainly not on all. In any case, while for practising scientists adopting Mariscal and Doolittle’s null hypothesis may be unproblematic, for metaphysicians it certainly is not a trivial matter and raises further metaphysical questions.
I do not think that Putnam’s examples of water, lemons, and so on, constitute good examples of natural kinds. Still, Putnam’s example serves well to illustrate how kinds depend epistemologically on their members.
Think of the Higgs boson at the time before it was found, or the heavy elements that so far have not been created in the laboratory (at this point, these are elements with atomic numbers higher than 112).
This compels me to say more about the troublesome debate on natural kinds. Straightforward realists about natural kinds should agree with me that there is ontological parity between a kind and its members: the kind exists independently of us, as do its member entities, and we learn about the kind and the characteristic properties of its members by studying some of the members, because we cannot study the kind as such. I am not a straightforward realist about natural kinds, however, and view kinds as groupings made by us but also supported by theoretically relevant aspects of the world (see Reydon 2016). At base, this is the view that was already expressed 330 years ago by Locke, who in the Essay held that nature makes things similar and different in numerous ways, while we group things according to those similarities and differences. This is a view that has found wide acceptance among contemporary authors on natural kinds, perhaps most prominently in Boyd’s HPC account of kinds. On this view, the ontological parity of kinds and their members can be thought of as ontological parity between kind members and the factors in nature that support the kind.
I thank W. Ford Doolittle for clarifying this matter in correspondence.
Note that only on a straightforward, strong realism about kinds one would have to say that kind terms refer to kinds that as kinds exist independently of us in the world. But most realists about natural kinds do not endorse such a strong realism. What would it mean to say that there are kinds “out there” in the world, after all? Rather, realism about natural kinds usually is taken to mean that groupings made by us reflect aspects of the world as it is independently of us. As Bird and Tobin (2018, first paragraph) put it: “To say that a kind is natural is to say that it corresponds to a grouping that reflects the structure of the natural world rather than the interests and actions of human beings.” On this view, the difference between realists and conventionalists about kinds is that conventionalists hold that all kinds are groupings made by us for particular purposes without representing aspects of the world, while realists hold that at least some kinds do represent aspects of the world, even though kinds are made by us. This is the sort of realism found with almost all realists about kinds from Locke via Putnam, Kripke, and Boyd to today. It is also a realism – a “weak realism” about kinds – that I endorse (see Reydon 2016).
I will have more to say on this in Sect. 4.
For another illustrative example, think of the mereological nihilism defended by, for example, Van Inwagen (1990).
At most, the theoretical context in which ‘Life’ as a proper name of an individual features is that in which names such as ‘D. melanogaster’ also feature as names of individuals. But as I showed in Sect. 2 and discuss further in Sect. 4, this theoretical context underdetermines what sort of individuals exactly we are talking about. There are a number of different ways to conceive of species as historical individuals, and this hold too for Life as a historical individual.
Note that I am not suggesting that the claim that the mere claim that species are individuals is metaphysically toothless. One benefit of Ghiselin’s and Hull’s proposal that species are individuals rather than natural kinds is that it makes sense of the fact that there are no laws of nature that range over all and only the members of a species. If species were natural kinds, one would expect that biologists would have identified laws of nature that range over them and use the names of species in the formulation of such laws. But there are no such laws, and this is not surprising because species are not the sort of entities over which laws of nature range, that is, they are not kinds (e.g., Hull 1976, pp. 188–189, 1977, pp. 95–96, 1978, pp. 353–354; Ghiselin 1988: 469). This benefit of more clarity about the question why there are no laws about particular species can be had on the basis of the mere claim that species are individuals rather than kinds – the bare claim thus does philosophical work. The point that I want to make, however, is that without further specification of any details the bare claim that species are individuals does not provide a satisfactory account of the metaphysics of species and thus falls considerably short of being a solution to the species problem. I am indebted to an anonymous reviewer for pushing me on this matter.
In this context I would suggest that ‘life’ is not a scientific term, but only a term of everyday language that can refer to anything we use it to refer to – the Tree of Life, the category of living beings, an individual organism’s trajectory of existence from birth to death, and so on. Philosophers of science, then, should stop worrying about the term, but not for the reasons Machery (2012) suggested. While Machery suggested that there are too many different scientific contexts in which the term features, such that trying to find one definition that covers them all is a pointless exercise, I suggest that there is no theoretical context with respect to which a definition would make sense.
A question, then, is how many different kinds of biological individuals need to be distinguished. One basic distinction is between evolutionary individuals and physiological individuals (Pradeu 2016b). Still other kinds of individuals can be distinguished, such as metabolic individuals, immunological individuals, Darwinian individuals, non-Darwinian individuals, and so on (Kendig 2018, pp. 1–2). This diversity of individuals is in line with current approaches in the philosophy of biology, in which individuality is treated as relative to research contexts, to the phenomena under study, to the questions that are asked, and so on (Kendig 2018, 4–5).
This suggestion is not new: Ereshefsky and Pedroso (2013, 2015) have made the same claim. This claim should not be mistaken for a claim that individuals are processes – a claim that is becoming increasingly popular due to the New Processualism in the philosophy of biology (Nicholson and Dupré 2018). The claim is that individuals only can be individuated in the context of processes in which they maintain their numerical identity.
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Acknowledgements
I would like to thank W. Ford Doolittle for helpful, constructive criticism of (and disagreement with) many of my points. I am also indebted to two anonymous reviewers and the audience at the workshop Biological Individuality and Other Issues in Contemporary Philosophy of Biology (Salzburg, September 2018) for helpful comments on earlier versions of this paper.
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Reydon, T.A.C. On radical solutions in the philosophy of biology: What does “individuals thinking” actually solve?. Synthese 198, 3389–3411 (2021). https://doi.org/10.1007/s11229-019-02285-8
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DOI: https://doi.org/10.1007/s11229-019-02285-8