Triceratops Against Concepts

Adrian Currie writes...

So, um, I’m starting to wonder if us philosophers focusing so much on ‘scientific concepts’ hasn’t been a big fat waste of time?

Lots of philosophers of science (myself included) like to think that we’re doing “philosophy of science in practice” (there’s even a society – the conferences are fantastic). As such, our work is supposed to be in some sense close to what scientists actually do—tracking the process of science—compared to other approaches which, for instance, focus on scientific theories, or the products of scientific investigation. A common motivation for philosophical reflection in this context is the idea that our philosophical work matters for what scientists do. It’s a lovely idea. But I’ve always felt a bit uneasy about this… To what extent can this kind of philosophy really feed into scientific practice?

This worry solidified when I read Karen Kovaka’s thought-provoking paper Biological Individuality and Scientific Practice (Karen read a draft of this post, and had some helpful criticism – thanks!). She’s interested in what philosophers call the ‘biological individuality problem’. The problem is pretty simple: we don’t know which biological objects are the individuals. Are the set of cells which share my genome—the Adrian-cells—an individual, or is the combination of Adrian-cells and all of those microbes within me (which I can’t live without) an individual? Is an ant an individual, or is the anthill an individual, or both? And so on. (Alison McConwell has a nice introductory piece covering these issues, oh and Leonard also just discussed it…)

Why should we care about the biological individuality debate? A common motivation appeals to real-life scientific work. Having an account of biological individuals in hand will enable biologists to count things, or get past the biases generated from their paradigmatic examples. The thought seems to be that there’s some conceptual housework to be done, and that housework is prior to some successful science being done.

But Kovaka doesn’t think the housework is prior. She points out that the difficulties philosophers point to can be—in fact often are—solved perfectly well by scientists without their claiming just what an individual is, and moreover that having an account of ‘individual’ in hand often won’t solve scientists’ empirical problems. Kovaka makes the sensible suggestion that the relationship between individuality concepts and what scientists actually do is one of what she calls ‘sensitivity’: roughly, there’s a dynamic interplay between conceptual and empirical work.

Now, I suspect that her philosophical interlocutors don’t actually think that their housekeeping is prior to scientific work in the sense she describes (and thus might take her point and happily jettison the housekeeping motivation!), but I really like how the paper encourages us to think about what motivates the kind of conceptual work that philosophers of science sometimes do. If Kovaka is correct, and often scientists don’t need to resolve conceptual problems in order to do their empirical work, that is, conceptual housekeeping is not prior to good empirical work, then appealing to our capacity to do such housekeeping in justifying our philosophizing is problematic.

But reflecting on the use of certain concepts in paleobiology, I’m starting to wonder if we should take a more extreme position.  Do scientists even use concepts in the sense we philosophers often talk about them?

To understand what on earth I might mean by this, I should start by telling you what I take a concept to be (for the purposes of this post). A concept carves up the world. A concept of x divides the xs from the not-xs. It is, in effect, a function from states of affairs to categories. A concept of biological individuality tells you what counts as a biological individual, and what doesn’t.

Now, this might strike you as a rather restrictive notion of ‘concept’ – and it is. But I think it’s pretty close to what philosophers seem to be worrying about when they have debates about scientific concepts (at least in philosophy of biology!). The specific set of concepts which I don’t see paleobiologists using are species concepts.

A species concept tells you what it takes for two critters to be part of the same species. I might say Super-Paw and Bailey (pictured below) are members of the same species because they have a unified ancestry, or because they are part of an interbreeding population, or because they have relevantly similar genomes, or so on. Like concepts of individuality, concepts of species are tricky. Many philosophers are pluralists about species concepts (they are about biological individuality too): there is not just one correct way of dividing species, but a group of ways, which are suitable for different tasks.

SP and Bailey, here representing two tokens of the same species. (image credit: Megan Delehanty)

SP and Bailey, here representing two tokens of the same species. (image credit: Megan Delehanty)

As in the individuality case, philosophers trying to understand species often take themselves to be interacting in some sense with scientific practice. The species-concepts they discuss are supposed to be those which scientists themselves use. At least, this was my assumption. Having grown up* reading philosophy and not all that much science, I expected that if I went and looked at how scientists went about telling which critters belonged to which species, they’d use the concepts. They’d ask ‘well, are they related?’ or ‘are their genomes similar?’ or whatever.

Basically, they’d feed empirical data into their favourite concept, and it’d spit out whether the critters were the same species or not. If that were the case, then philosophical accounts of species concepts are very likely to feed directly into scientific work.

How I expected scientists to use species concepts (using an interbreeding criterion for example).

How I expected scientists to use species concepts (using an interbreeding criterion for example).

But so far as I can tell scientists don’t use concepts like this. At least not in paleobiology. Which brings me to the Triceratops.

As I discussed in my last post, there’s been a kerfuffle about how best to categorize late Cretaceous ceratopsids. Where traditionally we’ve thought that there were two genera hanging out at the K-Pg boundary—Triceratops and Torosaurus—a new view (the ‘Toroceratops hypothesis’) has it that in fact the two are different ontogenetic stages of the same lineage. Specifically, Triceratops are young Torosaurus. If this debate were played out as I sketched above, we’d expect the various sides to be either disagreeing on what it took to be a species (that is, about which species concepts were applicable), or whether the evidence was sufficient to establish that these were indeed species according to a specific concept or set of concepts. This is not what we see.  To show this, I’ll sketch some of the debate.

The original argument, made in 2010 by John Scannella and Jack Horner, roughly had it that if you kept a Triceratops growing, it would turn into a Torosaurus. Triceratops skulls go through a lot of changes during their life-times. Look at the shifts in horn position:

Tricetops skull morphology from infant (a) to "adult" (e) from  Horner & Goodwin (2006)

Tricetops skull morphology from infant (a) to "adult" (e) from Horner & Goodwin (2006)

As they mature, Triceratops’ skull changes dramatically: shifting from backwards facing horns, with a spiky crest, to forward facing horns, with a wider, smoother crest. Their skulls have a developmental trajectory which, if ‘ran forward’ would (according to Scannella & Horner anyway) lead to a Torosaurus skull. They further argued that triceratops specimens present the porous tissue of young age, while Torosaurus have the more condensed tissue of the aged. Moreover, they say, there are no plausible examples of young Torosaurus. Finally, both genera overlap significantly in strata: they don’t present the differential appearance at different stages of the fossil record indicative of differences in species.

Notice what Scannella and Horner are arguing. They point out various features of Triceratops and Torosaurus: their developmental trajectories, patterns of dispersal in the fossil record, the nature of their tissue. They then ask what these features are signals of. And conclude that they are signals of ontogenetic differences: one is the younger version of the other. This is as opposed to them being signals of differences in evolutionary history: one being a member of a separate lineage from the other. This becomes even clearer when we consider some objections.

One direct objection focuses on the holes in the Torosaurus frill:

Triceratops  vs  Torosaurus  skull (Image credit: Dinosaurs by W. D. Matthew (1915); public domain.)

Triceratops vs Torosaurus skull (Image credit: Dinosaurs by W. D. Matthew (1915); public domain.)

As Triceratops are hole-less and Torosaurus are enholed, Scannella and Horner need to say that the holes develop late in ontogeny: only the oldest ‘Toroceratops’ developed them. But is this plausible given what we know about ceratopsid development more generally? Other lineages with Torosaurus-like holes sport them from earliest development. In more complex challenges, Maiorino, Farke & Piras (2013) provide counter-developmental-trajectories for triceratops which place Torosaurus in distant areas of morphospace and Longrich & Field (2012) argue that they can identify both elderly Triceratops and juvenile Torosaurus (and skulls like the one featured here certainly look pretty elderly, amiright?).

These arguments are not about the applicability of various species concepts. There is no movement from a state of affairs to category membership via a concept. Rather, they ask whether the patterns seen across the relevant specimens are better explained by differences in evolutionary history or the kinds of things which underlie variation within species. In the former case, we can appeal to evolutionary drift, the force of natural selection, and so forth, to explain differences. Torosaurus and Triceratops have different skull morphologies because of their shaping over evolutionary time. In the latter case, we can appeal to pathology, sexual dimorphism or developmental stages. Torosaurus and Triceratops have different shaped skulls because they are at different life stages, say.

You might complain that this result is simply due to palaeontologists working with fragmentary data—that if they could apply species concepts then they would. I’m not convinced. For one thing, it seems like the explanatory debate I’ve sketched above is where the action is. For another thing, in my last post I discussed the recent argument that living Little Blue Penguins actually represent two different species. So far as I can tell, here too we don’t appeal to concepts of the type philosophers use—what matters is whether inter or intra species processes are to blame for the patterns we have discovered in penguin populations.

Why does this matter? Recall that (1) philosophers appeal to their work having upshots for scientific practice in motivating and justifying said work. This (2) seems to involve the idea that philosophers discuss the kinds of concepts which scientists use. But (3) scientists don’t use concepts as philosophers discuss them. This (4) suggests, at the very least, that it’s not obvious how philosophical work is supposed to feed into scientific work. For myself, I don’t think this is a big problem, as I tend to think that philosophers have more to learn from scientific practice than we have to give to scientific practice. Moreover, there are many reasons to care about species and individuality concepts which are not do with helping out scientists in their day-to-day work. However, I think this should motivate us to be more reflective about what the relationship between scientific practice and engaged philosophy of science is supposed to be and moreover to be (and this echoes Kovaka’s point) more careful when we appeal to our capacity to ‘help out’ scientific practice when motivating our philosophical work.

Finally, I’ve just provided a few examples of how scientists delineate species which don’t appeal to species concepts – and I haven’t argued that these are representative. So, does anyone have any cases where it does look like scientist are using concepts in the way that philosophers think of them (and is there reason to take them as anything other than operationalizations?)? And, if I’m right, what kinds of justifications are there for thinking about scientific concepts in the philosopher’s sense? For me, ‘because I want to’ is actually a pretty good reason – but I’d love some better ones too…

* ‘grown up’ in the ‘whilst doing an undergraduate degree in philosophy’ sense…