A misguided philosopher claims that species don’t exist

July 17, 2019 • 9:15 am

I won’t say that philosophers in general have nothing to contribute to debates about the nature of biological species, but this philosopher certainly does: Henry Taylor, a fellow in philosophy at the University of Birmingham. His paper in The Conversation (click on screenshot below) not only says that the most used species concept in evolutionary biology—Ernst Mayr’s “biological species concept” (henceforth “BSC”)—is not only wrong, but that we should in fact have no species concept. Ignoring nature completely (has he been outdoors?), he concludes that nature is not divided into the discrete groups that gave rise to the notion of species. Rather, he thinks, nature—like some ideologue’s notion of biological sex—is a continuum. In fact, he concludes that “there is no such thing as ‘the human species’ at all.”

Well cut off my legs and call me Shorty! My whole life I’ve been interacting with (and mating with) what I thought were specimens of Homo sapiens. Now I find that I’m mistaken: we form a continuum with other species. Could I have mated with a chimpanzee or a badger by mistake?

Taylor’s list of publications gives exactly one (forthcoming in Synthese) related to the notion of species, and manages to make a big to-do about a geographically isolated population of brown bears that can hybridize with brown bears and polar bears. That is one of his beefs about the BSC, which I discuss below the screenshot:

The BSC is not really a definition, but, as I emphasize in my book Speciationwritten with Allen Orr—an attempt to encapsulate in words the palpable lumpiness in nature that we see before us.  And nature, at least in sexually-reproducing species, really is lumpy: it’s not the continuum, or “great interconnected web”, that Taylor sees. In Chapter 1 of Speciation, I give three lines of evidence for the reality of species: they aren’t just artificial constructs, or subjective human divisions of a continuum, but real entities in nature. Yes, there is some blurring in both sexual and asexual organisms, but by and large species exist as “lumps” in the pudding of Nature. If this were not so, biologists would be wasting their time studying species, and field guides would be of no use. There is no blurring, for instance, between our species, chimpanzees, and orangutans, nor between starlings, hawks, and robins on my campus. And so it goes for most of nature. Some hybrids may be formed between species, but they are often sterile or inviable, and so don’t blur the boundaries between groups.

What Mayr and others (e.g., Theodosius Dobzhansky) did was simply to describe what kept these lumps separate from one another where they coexist in the same location. And that factor was reproductive isolation: the existence of genetic barriers to hybridization that kept two species living in one place from forming fertile hybrids, and thus kept their gene pools separate. The BSC is this:

Members of different species are unable, when they live together in the same area, to hybridize and form fertile offspring: they are “reproductively isolated”.  Members of the same species are able to mate and produce fertile offspring with other members of the same species. 

Coexistence, or “sympatry”, is important in this determination because geographically isolated populations that show some differences can’t be fully tested under the BSC since they don’t encounter each other in a state of nature, and some species that hybridize in captivity don’t do so when they encounter each other in the wild (e.g., lions and tigers, which used to coexist in India).

There are of course intermediate cases—groups that are more or less “species-like”—depending on how much hybridization and gene flow they experience. But for sexually reproducing organisms, these cases are the exception (see Chapter 1 of Speciation). And of course, as we emphasize in the book, the BSC cannot be applied to species that lack sexual reproduction—like many species of bacteria. In those groups one may have to use other species concepts.

The advantage of the BSC is that it gives us an empirical program for studying how lumpiness arises in nature: it arises by the formation of genetic barriers, almost always between isolated populations that experience divergent evolution to the extent that, eventually, gene flow becomes impossible. (The barriers to gene flow aren’t directly selected for in most cases: they are simply byproducts of divergent evolution.) As I pointed out in my chapter, virtually everyone studying speciation in biology (as opposed to defining species), studies the origin of reproductive barriers. That’s a tacit admission that speciation does have something to do with reproductive isolation.

I won’t go on here: I recommend Chapter 1 of Speciation (it’s accessible to the layperson who knows a bit of biology), and, if you want to see the failures of other species concepts, read the Appendix.

Now, why does Taylor reject the BSC, and along with it all species concepts? He gives two reasons.

1.) Polar bears and grizzly bears, once living in different places (“allopatric”) are now meeting each other in nature due to the global-warming-induced disappearance of the cold habitat to which polar bears were once restricted. There is some hybridization between the two groups that now meet, and some of the hybrids are fertile.

Taylor says this shows that the two bears weren’t reproductively isolated, and thus weren’t species. But this is bogus: the two groups were biological species, isolated by what we call “ecological isolating barriers”: genetically based preferences for different habitats that kept two species from encountering each other. (The genetic basis of habitat segregation is important here: two groups isolated simply because they’re on different islands aren’t necessarily biological species because their spatial segregation is due to the contingencies of geography and not to evolution.) Thus the polar and grizzly bears were separate species, but their genetic barriers broke down due to climate change, making the differential habitat preference nonfunctional.

Species may not be permanently different: all of us recognize that groups that remain distinct in nature can, in the future, exchange genes because their genetic barriers have been circumvented by environmental change. Plants kept apart in nature because they are serviced by different pollinators (“pollinator isolation”) may, in the future, suddenly begin hybridizing if one of the pollinators goes extinct. Changes in habitat can efface genetically based ecological preferences, and so on. If you put lions and tigers together in zoos, this breaks down both the geographic and sexual preferences that kept them separate when they used to coexist in India. They can then hybridize and form fertile “ligers” or “tiglons”. Does this mean that lions and tigers are the same species? No, because the change in habitat (artificial confinement in this case) has broken down their genetically-based isolating barriers.

To say that the BSC is bogus because polar bears and grizzly bears now hybridize in some places is to throw out the baby with the ursine bathwater. And this isn’t even an intermediate case: it’s a case where a barrier has been effaced by climate change.

2.) Taylor then trots out the old canard (if ducks can trot) that organisms that don’t interbreed can’t be subject to the BSC. DUH! This is something I discuss at length in Speciation. Taylor:

The [BSC] definition makes use of the notion of interbreeding. This is all very well with horses and polar bears, but smaller organisms like bacteria do not interbreed at all. They reproduce entirely asexually, by simply splitting in two. So this definition of species can’t really apply to bacteria. Perhaps when we started thinking about species in terms of interbreeding, we were all just a bit too obsessed with sex.

Indeed, it’s hard (but not entirely impossible) to imply a reproductively-based species concept to bacteria. But different species do exchange genes, and there have been several attempts to discern bacterial species using reproductive criteria. The question hinges on whether there’s a problem to explain in bacteria: are they “lumpy,” like sexually-reproducing species, or do they form more of a continuum, and thus there’s not a biological observation that needs explaining? This question isn’t yet settled.

And that’s it: Taylor’s lame effort to topple the BSC—a concept that was not even meant to apply to asexual organisms.  He then throws into the mix Darwin’s own confusion about what species really were (this is well known) and on that basis wants us to deep-six all species concepts and all ideas that species even exist as discrete entities independent of human judgment. (Tell that to a robin who is courting other robins but not pigeons! Animals are themselves good taxonomists!)

Here you go:

Scrapping the idea of a species is an extreme idea: it implies that pretty much all of biology, from Aristotle right up to the modern age, has been thinking about life in completely the wrong way. The upshots of this new approach would be enormous, both for our scientific and philosophical view of life. It suggests that we should give up thinking about life as neatly segmented into discrete groups. Rather, we should think of life as one immense interconnected web. This shift in thinking would fundamentally reorient our approach to a great many questions concerning our relation to the natural world, from the current biodiversity crisis to conservation. [JAC: Yeah, what would we now conserve if all of nature is one interconnected web? Would we need to conserve everything?]

And, in a way, this kind of picture may be a natural progression in biological thought. One of the great discoveries of evolutionary biology is that the human species is not special or privileged in the grand scheme of things, and that humans have the same origins as all the other animals. This approach just takes the next step. It says that there is no such thing as “the human species” at all.

That last sentence is risible: there is no species Homo sapiens?! Does Taylor know that we cannot form fertile offspring with any other species (yes, it’s been tried with our closest relative: inseminating female chimps with human sperm produces bupkes). And it’s not the “next step” in dethroning humans as the pinnacle of evolution to then say that they don’t exist as a group.

The danger here is that those who don’t know much about biology and evolution will read Taylor’s piece and think he’s onto something. He isn’t: these criticisms of the BSC have been made many times before, and dispelled equally many times—I do it in my book, which is 15 years old. The palliative for Taylor’s nonsense—and here I have to be a bit self-aggrandizing—is to read Chapter 1 and the Appendix of Speciation.

h/t: coel

74 thoughts on “A misguided philosopher claims that species don’t exist

  1. This post is now essential reading for my undergraduate students enrolled in the class I teach on Evolution. Thank you.

    1. In my class, I have been trying out a bit of Jerry’s informal terminology about species, as it has been both interesting and useful. There are ‘good’ species, which are the ones that reproductively isolated at least to the point that any hybrids were essentially sterile. For example, horses and donkeys. Then there are various other species that are not ‘good’. These hybridize and the hybrids are viable and at least semi-fertile. A nice example are wolves and coyotes.
      So speciation is a divergence process, and in the early stages the incipient species can still hybridize. But if divergence has penetrated to aspects of reproductive compatibility (chromosome arrangements, mating times, etc.), then they become ‘good’.

  2. The tired “false dichotomy” is at play here. One may still “think of life as one interconnected web” even while acknowledging the existence of species. The two are not opposing views.

    What’s wrong with him?

    1. Too much philosophizing in an isolated room? He seems to be missing the “check your ideas against reality” bit.

    2. “What’s wrong with him?”
      He still has not noticed that the “interconnected web” is a notion in space-time (at least about 4 billion years of it in the usual reference frame) whereas “species” is an instantaneous notion (or at least periods of time relatively short in this context).
      But you hardly need the explicitness above to see the point, unless your job is in a 3rd rate philosophy department.

  3. Nice post. There is a crew of musicologists who use very similar arguments and claim that the historical musical periods (Renaissance, Baroque &c.) didn’t really exist.

  4. Could I have mated with a chimpanzee or a badger by mistake?

    Oh, I think you’d know if it were a badger. Especially if you were doin’ mish. The badger’s a beast that fights best on its back. It tends to fix all four claws on the throat of whatever’s on top.

    1. You need to insert a disclaimer in some of your posts Ken. ‘This is not drawn from personal experience’; something like that…

      1. Only with badgers. If a porcupine is your object of desire a different approach may be required.

  5. “The upshots of this new approach would be enormous, both for our scientific and philosophical view of life. It suggests that we should give up thinking about life as neatly segmented into discrete groups. Rather, we should think of life as one immense interconnected web.”

    Thinking of life as one immense interconnected web is already a common thing, has been for quite a long time and the BSC doesn’t conflict with that idea at all. Life is an interconnected web. We are all, from slime molds to humans, related, share the same ancestors and live in the same planetary ecosystem. But the BSC doesn’t conflict with any of that. Rather, it helps explain it. This philosopher is just being too simplistic or perhaps too enamored of blazing a new trail.

    1. Quite so. If life is one immense interconnected web there will be nodes and linkages, otherwise life is one immense bowl of porridge.

  6. So old-fashioned. The sort of things English sixth-formers talked about in the 1960s while idling (most of the time) and waiting for the school bell and a visit to a an espresso coffee shop. The guy clearly hasn’t read much. But then what do you expect from the stafff of a British university nowadays?

  7. … inseminating female chimps with human sperm produces bupkes.

    But they’re such cute little bupki, at least while they’re babies.

  8. If it would help (and this fellow makes me think it would), I am perfectly willing to do away with the false category of Philosophy.

    This shift in thinking would fundamentally reorient our approach to a great many questions concerning our relation to the natural world, from the current biodiversity crisis to conservation.

    Taylor knew where he wanted to wind up, and, shockingly, managed to get there without a sweat. It’s little more than sophistry.

    1. And that conclusion is far from justified by his argument. if there are no separate species, then there is no such thing as endangered species! So looks like I can have some of that so-called white rhino brisket to-nite! Mmmm–mmm.

  9. What an odd approach to whatever problem was bothering him when he started writing that. I’m surprised he didn’t offer a solution, like maybe biologists need to use bigger categories as well to look at nature — something like maybe, species genus family order class…

  10. Chapter 1 of Speciation is the go-to on this topic with some who know little of biology too. I used it recently to help my young nephew and his friend who were fascinated (but deeply confused) by ligers and tigons and other weird hybrids. They understood easily.

  11. Taylor has contributed one more confusion into scientific understanding. But, he did get a publication out of it.

  12. This is the ‘going nuclear’ approach to philosophical debate.

    The same arguments this guy applies to the concept of distinctions between species could just as easily be applied to _any distinctions that anyone makes, anywhere._

    Eg., I could quibble with him whenever he uses the word ‘person’, by pointing out that more than _half_ of all the cells in a person’s body are non-human. Are they part of that ‘person’?
    What about the terrifying face mites that live on everyone’s face?
    What about when someone cuts their hair? Are they diminished as a person? They’re shedding their own DNA in the process after all.

    These same arguments apply to everything that we, for shorthand, identify as a single, distinct entity.
    If I remove parts of my car, at what point does it stop being a distinct car and become a jumble of parts?
    At what point does a grain of sand, and another grain of sand, and another grain of sand…become ‘a pile of sand’?

    You could argue that the only reliably distinct entities in the universe are found down at the molecular level – everywhere above it the concept of making clear distinctions between objects breaks down.

    So we use shorthand, and we ignore the conceptual flaws in the idea of distinctions, because otherwise it would be impossible to reference real world objects in a consistent, timely fashion.

    If he’s going to attack the idea of distinct species on this basis then he should follow his argument through to its conclusion and admit that the very idea of distinctions doesn’t really make sense. In doing so he’d have to admit that 90% of everything he says is gibberish.
    He doesn’t of course; he wants to confine this critique solely to speciation. But it doesn’t work like that – if you go nuclear, then you have to face up to the fallout.

    1. What an iconoclast! There is sooo much science we’ve been doing wrong!

      For example: the ideal gas law is clearly false. This property we call “pressure” is, in reality, the accumulated force of gas molecules bouncing off the interior surface of a container. Instead of relying on such an obviously wrong and crude approximation, we should direct our efforts toward precisely measuring the momentum vector of each molecule and adding up the force applied to all parts of the container’s interior wall. It’s the only way to *really* understand what’s going on. 😀

      1. Exactly. It’s philosophical juvenilia.

        It’s child’s play to pick at threads like this. Every biologist on earth understands that the concept of a species isn’t rigidly, logically precise. So what?

        His critique could just as easily apply to 99.9% of all distinctions that humans have ever made. And, to paraphrase Popper, when a critique applies to everything, it applies to nothing.

  13. So the “extinction crisis” is not a crisis at all, since if there are no species then nothing goes extinct.

    1. “Also, the concept of a ‘crisis’ is fuzzy and indistinct, and can be taken in many different ways; for example, the great war of 1914-1918 was seen as a crisis, but so was the splitting of the pop beat combo The Beatles, etc….”

      It’s like philosophical pedantry 101.

  14. Taylor’s argument is nonsense, of course. But it is also true that life is a continuum historically, and that the concept of species is fuzzy at the edges.
    We can’t define a point at which the first homo sapiens was born to a mother from an ancestral species.
    Species is an artificial concept that is useful and captures some of the lumpiness of nature. Nature is messy, and we use categories to help us understand it. But we shouldn’t think that such categories are well-defined and rigid.
    ‘River’ is another example. There are real rivers, but when you try to pin down what is and isn’t a river, or whether this is the same river as it was 1000 years ago, you can’t.

  15. Also dead stuff and living things are a continuum; so all living things are really dead.

    Philosophy is easy.

  16. Thanks for that great post. Why does a philosopher not check around before putting this out in print? Does he not care about the reputation or is his fall back excuse – well, I’m really not an expert in the field, I’m just pretending to be.

  17. “X eliminativism” is a standard possible position in philosophy. “Species eliminativism” has been tried before – by any consistent nominalist. One has to refute nominalism by nonbiological examples, though, since biological kinds are vexed.

    I think, however, that this person wants to meld that approach with the usual criticisms of the BSC, which have been pushed a bit too much here.

    To help clarify my own thinking: what “governs” whether lateral gene transfer and such is possible?

  18. Henry Taylor: “Rather, we should think of life as one immense interconnected web”

    Wikipedia: “the biosphere is the global ecological system integrating all living beings and their relationships”

    Nothing new here.

  19. Activist: Hmmm…I have this social good I’m trying to promote…and let’s see, if biology worked in this simple and precise way…oooh! That would support it! [publish publish publish]

    Scientist: biology doesn’t work that way. Also, biology is messy; there’s probably not any set of ‘simple and precise’ rules that will accurately describe it.

    Activist: so I have to give up on my social good?

    Scientist: no, go for it. Just please – for the umpteenth time – leave us and nature out of it.

  20. *Sigh* Another philosopher, unencumbered by facts, decides that all the biologists are wrong. What is bizarre is that he had some idea what the BSC was, so why not have a modicum of curiosity to discover why biologists even claim that there are species?

  21. From Dr. Taylor’s bio on The Conversation:
    “I am also interested in how all this works in the biology. For example I am fascinated by the fact that the concept of a ‘species’ is the most important concept in all of evolutionary biology, but there is zero agreement amongst biologists about how to define it, or what it might mean.
    One fun upshot of this is that the question of whether whales are fish turns out to be way more complicated than perhaps we may have thought!”
    Perhaps some actual biologists might care to comment on the “zero agreement” in the definition of species; it seems to me that there is substantial agreement, and when there is difference it is often because the use made of the term “species” differs. Geoffrey Watson, commenting on the original article, said:
    “This is an interesting question, but its importance differs depending on whether you are inclined to regard a species as a “natural kind” that exists “out there”, or whether you think of it as just a useful concept in classification. I take the latter view, so the big question is not “do species exist” but “why is this concept so useful in discussing and theorising about life”.
    The issue of how do we define a species is important in either case, but the lack of agreement and multiplicity of definitions is to some extent a result of the many different contexts that the concept is used. For example, like bacteriologists, palaeontologists can’t use interbreeding as an indicator but neither can they use DNA and have to depend on morphology.”
    Taylor seems to think the definition of “species” is prescriptive, most of his critics make it clear that they see it as observational, for lack of a better word.
    As for whether the question of whether whales are fish is complicated or not, well … that turns on your definition of “fish”.

  22. “Rather, he thinks, nature. . .is a continuum.”

    Isn’t this old hat? I seem to recall that Alexander von Humboldt proposed this idea around the turn of the 19th century.

  23. His personal profile on the Birmingham Uni website says he’s interested in philosophy/psychology and metaphysics. He should stick to that and stay well away from subjects such as biology, where his knowledge and understanding are those of a 14-year-old.

    Jerry, why not send your article to The Conversation as a rejoinder? You never know, they might even post it!

    1. I think it’s great when philosophers and social scientists want to study more hard science. We should all be so open to new knowledge. The problem here is Dunning-Krueger; someone not knowing much in the fix of not knowing how much they don’t know.

      1. The sad thing is that there *are* philosophers of biology who could have provided in-discipline rejoiners, too.

        In fact, if I recall, Sterelny and Griffith’s now *20* year old textbook addresses views of species and speciation.

  24. Let me preface this comment by saying that, of course there are species. The fact that there are a few hard cases doesn’t make the general concept wrong. However:

    Taylor says this shows that the two bears weren’t reproductively isolated, and thus weren’t species. But this is bogus: the two groups were biological species, isolated by what we call “ecological isolating barriers”: genetically based preferences for different habitats that kept two species from encountering each other. (The genetic basis of habitat segregation is important here: two groups isolated simply because they’re on different islands aren’t necessarily biological species because their spatial segregation is due to the contingencies of geography and not to evolution.) Thus the polar and grizzly bears were separate species, but their genetic barriers broke down due to climate change, making the differential habitat preference nonfunctional.

    This argument doesn’t work very well for me. It seems like the argument is saying that grizzlies can’t survive in polar bear environments and vice versa, so they don’t mate and therefore are separate species. Except climate change has shown that the two species can coexist in the same environment which invalidates the argument.

    I would have thought that, if there was a barrier, climate change would just move it North rather than dissolve it. Also, how do we know that polar bears and grizzly bears haven’t always been bonking with each other at the margins of their territories but nobody noticed because they weren’t looking until climate change gave them an incentive.

    1. The question is not whether they CAN coexist in the same environment (tigers and lions can), but whether in nature they DON’T–and that geographic disjunction is caused by genetically based habitat preference. That is an evolutionarily created isolating barrier. Perhaps polar bears are now evolving to tolerate warmer temperatures, and that’s one reason why they can live in warmer climes (and mate with grizzlies). If the argument doesn’t work well with you, read our chapter on Ecological Isolation.

      1. I guess if one wanted to check such hypotheses the sticking point would be “genetically based habitat preference”.

        Philosophers would point out that this immediately runs into *another* debate, namely the “gene for” one, etc.

    1. He would argue that there is no such thing as a lumper-splitter spectrum and we should view everyone as lumpers.

      Frankly, I’m surprised. Don’t philosophers learn about the continuum fallacy?


  25. Jerry do you think it would be helpful if we sometimes gave names to the unoccupied phenotypic gaps between species? I think of them as names for the empty white spaces in between the branches of a phylogeny. Those names would be a sort of guard rail that would possibly help prevent novices like Henry Taylor from veering off track. His argument seems to have collided with the lumpiness of nature in part because he didn’t recognize the existence of some of those unoccupied (and maybe unoccupiable) spaces between the lumps of organisms. I suggested this once in a paper (DOI: 10.1111/j.1558-5646.2010.01202.x) but the idea hasn’t caught on, possibly for good reasons 🙂

    1. One problem I’ve had with cladistics is *naming* – which sounds trivial, and technical vocabulary does not need to reproduce ordinary language. Yet I find it difficult to find good (“suggestive”) names for all the nodes of the trees. (Not that it is up to me, of course, but hypothetically.)

  26. Ahh, the definition trick. You really cannot define anything with infinite precision. You cannot even define “chair”. Try it; no matter your definition I will be able to find a borderline case where your definition fails. Conclusion: there are no chairs.

    1. Joking a bit here, but be careful with “anything”!

      I define the object for which the symbol 3 is one of many notations, having already dealt with ‘1’ and ‘+’, to be the object for which another notation is ‘1+(1+1)’.

      Is not that a perfectly precise definition? (I was fed up with merely ‘1+1’.)

        1. I’d take your “factual science” to include physics, in particular fundamental particles.

          If so, then I believe the word ‘electron’ has a completely perfectly precise definition there. (Maybe?) it is simply a fundamental particle of charge -1 and minimum mass among such particles, to eliminate muons and tauons, and also W- though saying ‘lepton’ instead of ‘particle’ does that also. And no sweat with the anti-matter particles. No two electrons differ in any internal property. Actually nice that it was the first particle discovered, circa 1897.

          Apparently no dark matter particle, should they, as likely, exist, has that charge (nor any charge?).

          1. That’s correct about the formal/factual distinction. As for the “definition” of “electron” – that’s one case where maybe it would be fine. My only problem would be “of minimum mass” – it seems to use a *referition”, i.e., a thing-sign correspondence, not a sign-sign one. This is fine; this is how most factual concepts get their “meaning”. This, however, has the feature that if we discover or have theoretical reason to believe in another particle which is like the electron as we understand it now (of mass m) except it has mass m/2. What then? The referition now points to that new particle, not the old one.

            Compare that to the formal case, where we cannot be wrong about the successor to zero in any given theory of arithmetic; there are no referitions in formal science as far as I can tell (or rather, there aren’t in modern such fields).

            1. We could of course specify the electron’s mass ‘exactly’ i.e. with error bars, but your same objection could be formulated. Presumably whatever property made the new particle to be known to be not an electron, then negated, would need to be added to the electron’s ‘definition’, likely badly ad hoc.

              On the earlier, have you ever seen the natural numbers defined to be that infinite well-ordering in which the subset of those less than a fixed element is always finite?

  27. This Conservation article is deeply flawed. Clearly, the philosopher is not up to date with the literature on the species problem. I have written a critique on my blog Avian Hybrids, explaining that we do know what species are. Namely, the species problem can be resolved by theoretical monism (the evolutionary species concept or general lineage concept) in combination with practical pluralism, in which different species criteria correspond to different stages during the speciation process.

    And for those interested, I recently published a book chapter on species concepts in ornithology and the role of genomic data.

  28. Great discussion. I wrote a piece that’s partly a response to this, from the angle of asking how categorization works more generally:


    I’d very much appreciate if any of you *actual* biologists could check my reasoning and explanations, as it’s entirely possible I’m full of bupke. 🙂

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