Gould on species, metaphysics and macroevolution: A critical appraisal
Introduction
Stephen Jay Gould's revisionist program for evolutionary theory (see especially his 2002) has generated widespread discussion and debate both within and beyond evolutionary biology. His views on the ontology of species were, in his mind, an important plank of this revisionist program. In this paper I cast a critical philosopher's eye over those views. I focus on three central aspects of Gould's views on species: the relation between the Darwinian and the metaphysical notions of individuality, the relation between the ontology of species and macroevolution, and the issue of contextualism and conventionalism about the metaphysics of species.
Gould defends views on both the first-order question of the ontological status of species, and the second-order question of realism vs. pluralism about the first-order question. In the first part of the paper I discuss his arguments for his first-order views. Gould's central argument is that the species-as-individuals thesis (SAI) follows from the macroevolutionary theses of punctuated equilibrium and species selection. In response, I argue that SAI is neither necessary nor sufficient for either of these theses.
In the second part of the paper I turn to Gould's arguments concerning the second-order question of whether to construe the first order question in realist or pluralist terms (or both). We will see that he defends a pluralist position that, at first blush, appears to conflict with his realist-sounding first-order arguments. There may be ways for him to reconcile his first-order and second-order views. But I suggest that these strategies are not ultimately successful.
Gould's views on the ontology of species are, in his mind, central to his whole revisionary program. They are, for instance, closely connected with his views on punctuated equilibrium, and higher-level selection. His co-thinker Niles Eldredge argues (1985) that the question of ‘ontology’ is the central issue for those, like Gould and himself, who are seeking to challenge the orthodoxy of the Modern Synthesis. Gould would no doubt agree with this claim. Hence if, as I will argue, Gould's views on the ontology of species are questionable, this may well have major significance for the viability of his overall project (although I am not able in this paper to go on to consider in detail precisely whether and in what ways this may be the case).
Throughout the paper it will be useful to compare and contrast Gould's views with those of another prominent defender of SAI, David Hull.
Section snippets
Gould on species, individuality and macroevolution
The question of the ontological status of species – whether they are individuals, natural kinds, sets, or something else – has been much discussed since Ghiselin offered his ‘radical solution to the species problem’ in 1974. In The Structure of Evolutionary Theory (2002) Stephen Jay Gould offers a defence of Ghiselin's species-as-individuals view.1
Darwinian and metaphysical individuals
It should first be noted that Gould does not clearly and consistently distinguish Darwinian from metaphysical individuality. Instead of viewing the fact that an entity is a Darwinian individual as a reason for thinking it's a metaphysical individual, he often seems to be saying that to be a Darwinian individual just is to be a metaphysical individual. So he suggests (1996) that the only question to ask about individuality in the natural world is the question of Darwinian individuality; if some
Species as individuals, species selection and punctuated equilibrium
It might be objected that it is something of a distortion to interpret Gould as arguing from species selection (and PE) to SAI. He as often seems to be arguing in the other direction, and sometimes seems to be arguing for both simultaneously. In fact I take Gould's strategy to be twofold: given the premise that SAI (in some sense) follows from PE and species selection (SS), he sometimes argues deductively that PE and SS are true, and thus that SAI is true; and other times he argues inductively7
Contextualism and pluralism about the ontology of species: Gould's second-order views
At the beginning I noted that the second premise in the main argument for SAI is often unacknowledged, but is arguably as important as the first. It is to this premise that I now turn. It reads:
If evolutionary theory treats, or should be interpreted as treating species as individuals, then they are individuals.
Although often unacknowledged by theorists, this premise is taken very seriously by both Gould and Hull. Their justification for it I will call the principle of theory-dependence
Conclusion
I have discussed three aspects of Gould's views on species. On the question of the relation between the Darwinian and metaphysical notions of individuality, I argued that Gould sometimes conflates the two notions, but that they are importantly distinct. On the issue of the relation between macroevolution and the ontology of species, I argued that SAI is neither necessary nor sufficient for either SS or PE. Gould and Hull may be correct that the idea of species as natural kinds in the
Acknowledgements
Thanks to Marc Ereshefsky, Kim Sterelny, John Wilkins, Greg Restall, and two anonymous referees for this journal for helpful comments and criticism.
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