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The Mystery of the Triceratops’s Mother: How to be a Realist About the Species Category

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Can we be realists about a general category but pluralists about concepts relating to that category? I argue that paleobiological methods of delineating species are not affected by differing species concepts, and that this underwrites an argument that species concept pluralists should be species category realists. First, the criteria by which paleobiologists delineate species are ‘indifferent’ to the species category. That is, their method for identifying species applies equally to any species concept. To identify a new species, paleobiologists show that interspecies processes, such as phenotypic plasticity (including pathology), sexual dimorphism, or ontogenetic diversity, are a worse explanation of the variance between specimens than intraspecies processes. As opposed to operating under a single or plurality of species concepts, then, paleobiologists use abductive inferences, which would be required regardless of any particular species concept. Second, paleobiologists are frequently interested in large-scale, long-term morphological patterns in the fossil record, and resolving the fine-grained differences which result from different species concepts is irrelevant at those scales. I argue that this claim about paleobiological practice supports what I call ‘indifference realism’ about the species category. The indifference realist argues that when legitimate investigation is indifferent to a plurality of concepts, we should be realists about the category those concepts pertain to.

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  1. But see Sober (1984), Wilkins (2003, 2009), Hull (1988), Ghiselin (1987).

  2. For instance, Kitcher (1984), Mishler and Brandon (1987), Dupré (1999), Ereshefsky (2001), Reydon (2004), O'Malley and Dupré (2007).

  3. See Mayr (1942), Dobzhansky (1937), Paterson (1985) and Ghiselin (1987) for variations.

  4. See Avise and Wollenberg (1997) and Baum and Shaw (1995).

  5. Again, this is an extremely simplified discussion, see Andam et al. (2010), Bapteste and Burian (2010), Bapteste et al. (2009) and Ereshefsky (2010) for more details on the relationship between species concepts, eukaryotes and other asexual organisms.

  6. A good place to look for skepticism about such a link is Kyle Stanford’s work, for instance his (2006).

  7. I skate over some subtlety here. Ereshefsky (2001) has pointed out that, if we don’t think there is an interesting difference between species and higher taxa, this is a kind of species anti-realism. If that is right, then my argument is for taxa-category realism, rather than species-category realism. I am comfortable with this—realism about some category is fine with me: I won’t quibble about whether we get to call them ‘species’. I return to these points in 6.4.

  8. Speculating about extreme changes in dinosaur life-stages has become de-rigour. It has been suggested, for instance, that the enormous sauropods both led very different lives in their juvenile and adult stages, for instance it has been speculated that they switched from fast-growing endothermy to relaxed ectothermy mid-life (Farlow 1990). It has also been suggested that Tyrannosaurus rex had two distinctive ontogenetic stages, a juvenile stage characterized by fast running speeds and feathers, and a slow, featherless adult packing a major bite (see Currie 1998; Erickson et al. 2004).

  9. Indeed, Schott et al. (2011) suggest this of pachycephalosaurus.

  10. See Schulte et al. (2010) for a view which emphasizes the role of the impact, and Archibald et al. (2010) for a view which sees it as one cause amongst many.

  11. See Roberts et al (in press) for discussion of the phenomenon.

  12. Pian et al. (2013), for example, introduce a new extinct platypus species, Odurodon tharalkooschild, largely on the basis that its enormous size outruns the expected phenotypic range of any other platypus.

  13. A nice case of an objection to species delineation on the basis of pathology is the suggestion in Barham (2004) that Homo floresiensis, the so-called ‘Hobbits’, are merely humans exhibiting microcephaly. In fact, taxonomy is the subject of voracious debate in paleoanthropology: see, for instance, the back and forth between Ian Tattersal and Matt Cartmill, which concluded with the memorable Tattersall (2013).

  14. Thanks to an anonymous referee for distinguishing between ‘indifference’ and ‘irrelevence’.

  15. Brandon Holter has suggested to me that indifference could come in degrees: that is, the identification criteria could matter more on some concept than others. He points to the ‘mate recognition’ species concept, whereby species are delineated via mating preferences which restrict gene-flow. Assuming the recognised features are morphological (rather than, say, hormonal), these criteria may matter more for that species concept than, say, a phylogenetic one. Formally, I take indifference to be binary, but I don’t think this matters for the argument herein.

  16. One way of stating this would be to claim that S forms a monophyletic clade of which f is a member, or that S is an historical individual of which f is a part.

  17. There is, in fact, one case of fossil organisms caught in an extremely extended coitus interruptus: a group of Eocene turtles (see Joyce et al. 2012).

  18. Note that paleobiologists frequently represent this information in terms of higher-taxa categories. This is typically because the fossil record is sometimes less biased when considered by genus or family.

  19. Thanks to David Leibesman for highlighting this problem.

  20. An analogous move is suggested in Lewis (1978).

  21. It may turn out that some paleobiological claims are indeterminate on this kind of view, and as David Leibesman has pointed out to me, this might involve exploring whether vagueness might undermine the link between practice and ontology.

  22. Naturally, for epistemic anti-realists such as Stanford and Rosenberg, this is less pressing. Although, if they are realists about various taxa which species concept pick out, there remains a tension.

  23. Marc Ereshesfsky raised this objection.

  24. I am thankful to an anonymous referee for raising this objection.

  25. This kind of objection could be made via appeal to work from the philosophy of mind on disjunctive properties. Hilary Putnam (1967), Block and Fodor (1972), Fodor (1974) have argued that disjunctive kinds are illegitimate. In that context, the argument centers on the nature of multiple-realizability: a large number of different substrates, in different arrangements, could potentially have what it takes to be a particular propositional attitude. It is likely, for instance, that a different neural correlate is involved with my thinking x than for your thinking x. However, it seems as if we can think the same x, that is, our xs can have the same content. If so, then either propositional attitudes should be characterized functionally (or in some other non-reductive way), or the identity theorist may accept a disjunction of those various substrates as a real kind. In rejecting identity-theory, then, philosophers of mind have argued against admitting disjunctive kinds into our ontology.

  26. Marc Ereshefsky raised this objection.

  27. Thanks to an anonymous referee for raising this objection.


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Brandan Holter, David Liebesman, Marc Ereshefsky and two anonymous referees provided extremely helpful feedback, as did the audience at the 2014 Boston Colloquim on philosophy of paleontology.

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Correspondence to Adrian Mitchell Currie.

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Currie, A.M. The Mystery of the Triceratops’s Mother: How to be a Realist About the Species Category. Erkenn 81, 795–816 (2016).

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