What are species? a Wittgensteinian approach

1. What are species? a Wittgensteinian approach

2. Warnings: This is a conceptual talk, and a very rough-drawn one. There are no data. There is no math. I don’t even cite people very often... Since most of the material is verbal, I’ve inserted various irrelevant images to keep your visual centers entertained.

3. Ludwig Wittgenstein One of the most influential philosophers of the 20th century. He was both a founder of logical positivism (in his Tractatus Logico- Philosophicus of 1921) and later one of its most prominent critics. His later work examined what language does, criticizing philosophers who used language divorced from its normal context to derive metaphysical systems.

4. The Wittgensteinian approach As a brief example of Wittgenstein’s approach to things, consider: Can we have knowledge of the external world? One traditional approach in epistemology, starting with Descartes (1641), is to say that: 1 we can’t be really have any knowledge as long as there is a possibility for doubt; 2 doubt about the evidence provided by our senses is always possible; we know that we are sometimes deluded and cannot be certain we aren’t always being deluded --> therefore, we have no knowledge of the external world. The Wittgensteinian response is: 1 we only use the word “knowledge” in cases where doubt is possible; this possibility is necessary for the word to have any function; 2 furthermore, the same is true for the idea of “reality”; a reality that we do not know or experience is a functionless concept.

5. Species Though species have long been considered the fundamental units of biodiversity and used as the basic referents in ecology, evolution, and conservation, how we ought to define and conceive of species is a long-standing controversy persisting with little apparent hope of resolution. The controversy is along several main lines: --which species concept? --one species concept or multiple? --are species individuals or classes? --are species real? I will talk primarily about the latter three. On species concepts I’ll restrict myself to saying that all definitions have problems. The biological species concept is inapplicable to both asexual and allopatric populations; the genealogical species concept can’t deal with clonality and causes over- splitting when applied to allopatric populations; etc., etc.

6. Species monism vs. pluralism Given that no single species concept appears to be universally applicable, a common suggestion is that maybe we just need more than one species concept. The situation is usually simplified to monism vs. pluralism--one absolute species concept vs. multiple equally correct concepts--but there are really three possibilities: pluralism 1 species type 1 S.C. 1 species type 2 S.C. 2 monism species type 3 S.C. 3 species concept species pluralism 2 S.C. 1 species S.C. 2 S.C. 3

7. Species monism vs. pluralism As it would happen, this is the only part of the species controversy to which a Wittgensteinian approach has been explicitly applied, by Pigliucci (2003). So I’ll briefly explain his solution. His is the only paper, as far as I know, to explicitly advocate type 2 pluralism. This is based on an analogy given by Wittgenstein for how complex terms (like “game”) in normal language actually work. The word is like a string with many strands; there is not a single definition that runs through the whole thing, but a series of related, overlapping definitions. one “game concept”; like “card game” or “board game” game

8. Species monism vs. pluralism one species concept; like “biological species” or “genealogical species” species And of course we can do the same thing for the word “species”. Just because there are different definitions doesn’t mean each one points to a different, independent kind of species. There need be no single, universal species concept, but rather a series of overlapping species concepts identifying different aspects of “species”. The failure of individual species concepts doesn’t mean we have to adopt multiple kinds of species.

9. Species monism vs. pluralism Another way to think of this: you have organisms in multi-dimensional character space and the question “Are these two separate species?” is “Do these two sets of organisms form mutually exclusive groups in character space?” Species concepts identify specific axes of character space to use in answering the question. For asexual lineages we can imagine something like this: genetic similarity reproductive isolation An interbreeding species concept would tell us to look at the horizontal axis whereas a genetic species concept would tell us to look at the vertical axis. They are simply different simplifications of the same distribution in multidimensional space.

10. Species: individuals or classes? The idea that we should view species as individuals was first put forth by Ghiselin (1974). So, what’s a class? Or an individual? A class is a set of objects that meet specified membership conditions. An individual is a specific object. Ghiselin suggested that we define classes, whereas we identify individuals; classes have members, individuals have parts; classes are time-independent, individuals have distinct beginnings and ends; “state” is a class, “California” is an individual. Well, OK, but what do these distinctions accomplish? And to what extent do they even exist?

11. Individuals or classes: definition vs. identification 1 So what’s the difference between definition and identification? One thing Ghiselin wanted to accomplish by this is to say that classes are created by a definition whereas individuals were already out there, just waiting to be recognized. This would mean individuals are real in some sense in which classes aren’t. But did California exist prior to its naming? Well, the land certainly existed, but could we say that particular chunk of land had a distinct identity before naming? Are its boundaries natural divisions that were there the whole time, just waiting for us to notice them? The US-Mexico border: natural feature or human construction?

12. Individuals or classes: definition vs. identification 2 So, some individuals, like California, are defined rather than identified. What about species, though? Should we say they are defined or identified, and does this have anything to do with the class/individual distinction? What Ghiselin really wants to suggest, by saying that we identify rather than define species, is that they are pre-existing objects that we point out, rather than little boxes we make and then shoe- horn organisms into. Can’t we just address that directly? Surely whether or not a species exists has something to do with data, rather than with what words we use.

13. Individuals or classes: eternal vs. historical Species have distinct beginnings and ends in time. Ghiselin argues that this means they are individuals, not classes. Individuals, such as specific people, chairs, states, etc., have distinct temporal beginnings and endings; classes, like “people”, “chair”, and “state” don’t. But what’s to stop us from including a common temporal origin and ending into the membership conditions of a class? For that matter, the name of an individual isn’t temporally limited, whereas the individual is. How is this really different from an eternal class with members that exist only for a time?

14. Individuals or classes: eternal vs. historical 2 Isn’t this just confusion between a name and the thing it refers to? Ghiselin seems to have a view of the situation like this: individuals classes name name class object object He thinks the class is some new thing stuck in between the name and the species. Then he’s bothered by this new thing not being temporally limited like the species are. But isn’t the name just a way of pointing to objects in either case? And aren’t we really interested in the characteristics of the species not of the names?

15. Individuals or classes: eternal vs. historical 3 On a more fundamental level, if you just want to make the point that species are historical entities, why drag the concepts of “individual” and “class” into it at all? Why not just say “species are historical entities” and be done with it? Furthermore, what is really the purpose of such an utterance? Are we in doubt as to whether species are historical, that we need Ghiselin to explain it to us? It seems like an explanation in search of a confusion.

16. Individuals or classes: typology Related to Ghiselin’s suggestion that species historicity requires species individuality is his rejection of typological species concepts. He and others have suggested that if we conceive of species as classes we inevitably fall into a typological view like that of pre-Darwinian taxonomists who adopted a kind of Platonic idealism in which species had fixed types, with individual organisms being imperfect copies of the type. This is another explanation in search of a confusion. Typology is already rejected, and should be rejected for being bad biology not for using words that imply bad metaphysics.

17. Individuals or classes: Ghiselin’s goals... So far as I can tell, Ghiselin had two main goals in introducing the idea that species are individuals. The first was to establish that species are real (to be discussed momentarily). The second was to advocate a specific species concept that he thought depended on the idea of species as individuals. On Ghiselin’s species concept, I’ll briefly make three points: 1 I find it somewhat incomprehensible; 2 it has not been taken up by any systematists I am aware of; 3 it is independent of species individuality. Ghiselin says species are: “the most extensive units in the natural economy such that reproductive competition occurs among their parts.” Suppose I say species are: “the smallest groups whose members are in reproductive competition”? The criterion used--reproductive competition--is independent of class- or individual-based phrasing.

18. Individuals or classes: what to do? So, are species individuals or classes? Whether we call species individuals or classes doesn’t change whether we view them as historical or eternal, whether we they exist prior to definition, what sorts of criteria we use to delineate them, etc. Do as you like. Call species individuals or classes if you want. Or don’t call them either one. Until someone makes the distinction operational, it doesn’t matter.

19. Species reality: are species real? This is often phrased as “are species real independent of our perceptions, or are they mental constructs we impose on our perceptions?” or the like... the question can be broken down into two components: 1 Are particular species real? 2 Is the species category real? I’ll worry about the first for the moment...

20. Species reality: type 1 So what is reality? As scientists we aren’t concerned with some sort of absolutist idea of reality hiding behind our observations; a strictly empirical definition of reality is the only workable one in science. This is a rather simple observation, yet it clarifies the situation. “Are species real entities independent of our perceptions?” The question doesn’t make sense. If reality is independent of perception, it’s not the kind of reality we want!

21. Species reality: type 1 In an empirical view of reality, there are really only two considerations when it comes to the reality of a named thing: Does it actually exist? Does it have the attributes we ascribe to it? If I say there’s a chair in the corner, I am wrong if there’s nothing in the corner, or if the thing in the corner isn’t really a chair... If I describe the species Larrea tridentata, I am wrong if the plants I describe don’t actually exist, or if they don’t fulfill whatever requirements we might have for species status.

22. Species reality: type 1 Or we can look at it another way. As in the earlier discussion of species monism vs. pluralism, we can view species definition as a claim about the grouping of organisms in character space. Determining whether a species is real, then, is just a matter of looking in character space and seeing if the set of organisms indicated actually forms a group. It is then an empirical claim, with empirical tests. A real species Not a real species

23. Species reality: type 2 Now let’s worry about whether or not the species category is real. It seems to me we can just apply the same reasoning. Suppose we go with the biological species concept, wherein species are the smallest groups of organisms that reproduce with each other. Then the species category is real insofar as organisms are actually divided up into such groups. If we looked into the world and saw only clonal, asexual lineages, we would conclude that the species category (so defined) is not real. If we saw sexual lineages forming groups with clear reproductive boundaries, we’d say the species category is real. What we actually see is some- where between the two.

24. Species reality: type 2 So if the species category, as defined in the BSC, receives good support in some groups (e.g., mammals) but poor support in others (e.g., some plants), do we conclude the category is real or not? This goes to a more fundamental question I can’t get into here. It depends on what the goal of the description is. If we are aiming for Truth (e.g., Popperianism), we must decide that the species category is not real. If we are aiming for explanatory power (e.g., Lakatosianism), we can either use a fuzzier definition of real, or reject reality as a criterion. Similarly, a pluralistic (type 2) species concept complicates matters, though not fatally.

25. Higher taxon reality a brief digression... Are genera, families, etc., real? I’m suggesting we evaluate the reality of the species category in reference to species concepts; in reference to what we’ve decided it means for a thing to qualify as a species. At the species level there are a number of competing concepualizations. At higher levels we have the opposite problem. We lack criteria to use in evaluating the question. If a genus is just a mono- phyletic group larger than a species and smaller than a family, we can detemine if such groups exist.

26. Summary In general I’ve been stressing two main points: What’s important with words like “species” is what we do with them. Different definitions or conceptions that don’t change what we do are just hot air. Reality is an empirical matter, not a matter of what words we use or what kind of metaphysics we want to come up with. Species reality is epistemological, not ontological.

27. Cited works: R. Descartes, 1641. Meditationes de prima philosophia. Published by someone a really long time ago. M.T. Ghiselin, 1974. A radical solution to the species problem. Systematic Zoology, 23(4): 536-544. M. Pigliucci, 2003. Species as family resemblance concepts: the (dis-)solution of the species problem? BioEssays, 25(6): 596-602. F. Pleijel & M. Harlin, 2004. Phylogenetic nomenclature is compatible with diverse philosophical perspectives. Zoologica Scripta, 33(4): 587-591. L. Wittgenstein, 1921. Tractatus Logico-Philosophicus, trans. by D. Pears and B. McGuinness. London: Routledge & Kegan Paul.