A new book correctly criticizes the idea that some species are superior to others, but mistakenly claims that species aren’t real

The Berkeley News, the publicity site for the University of California at Berkeley, has a piece out announcing a new book that was published out in December (photo below). Since it was published by the venal and greedy Springer, the hardback of Speciesism in Biology and Culture will cost you only $159.

Click on the screenshot below to read about the book, which comprises nine essays rejecting humans’ view that we are the top and most important species, and that species can be ranked by their “superiority”. With that rejection I wholeheartedly agree. But there’s another theme, too: one which I think is misguided: species aren’t even real. Click below to read the article, which has a summary of the book.

Here are the book’s two themes:

In a new book, a group of scientists and philosophers places part of the blame on an attitude prevalent among scientists and the general public — the false belief that species are uniquely real, and that some species are superior to others.

To the researchers, this is analogous to racism — the fallacious belief that races exist as branches on the tree of life, and that some races are superior to others.

Now I agree that there is no hierarchy of species: we just happen to be the one that evolved a big brain with which we can control all other species, and an organ we can use to pat ourselves on the back as better than others. (A flea doesn’t have the capacity to see itself as superior to other species—but it can suck their blood!).

But the view that species are not “uniquely real” is a gross distortion. Species are far more real and discernible than human “races”, whose demarcation is somewhat subjective although even the “classic” races are not totally invented social constructs (they contain biological information).

If species weren’t real, however, there would be no problem of “the origin of species”, and nature would be a spectrum—a rainbow with no joints between its constituents. Orangutans, gorillas, and humans would all be arbitrary entities: “social constructs”. So would pigeons, starlings, robins, and cardinals. But I’m getting ahead of myself. A few more excerpts about the supposed non-reality of species:

Mishler has argued for decades against considering individual species as the most important grouping, particularly when discussing conservation. [JAC: actually, in the U.S. it is subspecies that are the units that must be conserved.] He laid out his arguments in a 2021 book, What, If Anything, Are Species? ( CRC Press), in which he proposed getting rid of taxonomic rankings altogether, including the binomial system for naming species that is used universally today. [JAC: As you know, this idea hasn’t caught on, nor will it.]

One key reason is that species distinctions are not equivalent across all branches on the tree of life. Bacteria that look identical may vary as much genetically as a dog from a cat, while some birds that live in totally different areas and look different can be nearly identical genetically. On the other hand, lineages — the sequence of organisms that have evolved from one another over millions of years — are consistent across all forms of life.

“Evidence shows that a species of amoeba does not mean the same thing as a species of fungus, animal or anything,” Swartz said. “And if species are not uniquely real, then where does that leave us? Is there anything that means the same thing across the tree of life? The answer to that question is: lineages. These are branches on the tree of life that maintain genealogical connections across time and space. They include children, or descendants, and their parents, or ancestors, on through animals broadly and their distant relatives. Lineages are branches across the tree of life.”

Throwing out the concept of species would eliminate the artificial dividing line that helps justify the belief that some species are more important. Instead, the authors maintain that humans are just one part of a genealogy connecting all living things. This interconnectedness forms an ecological web that sustains the planet and us, and that deserves to be protected equally with humans.

Mishler goes one step further, arguing that lineages should be respected — not for how they can benefit humans, but intrinsically, as part of the web of life. He detests the term “ecosystem services,” which implies that the natural world exists to service humanity.

. . .The authors point out that the standard definition of a species is a population that cannot breed with closely related populations. But Mishler said this definition is muddied by the fact that there is often wide variation within a breeding population; sometimes two separate species can and do successfully interbreed, and some species don’t breed at all.

. . .“Alan Templeton summarized it most succinctly: The trouble with species is too little sex and too much sex,” he said. “There are asexual groups that don’t do sex at all, but still have lineages. And then there are plants, like the orchid, which can just about be crossed with every other orchid, yet they’re bizarrely different from each other. So, reproductive compatibility, while a nice idea, just doesn’t work empirically.”

Species also can evolve because they get separated geographically or ecologically, not because of an inability to breed.

A more natural grouping is by lineage — ancestor-descendant pairs connected across time — or by clade, which consists of all the descendants of a creature.

Mishler and his colleagues have argued for years that species aren’t real, but their views haven’t gained any traction in the biological community beyond those few people who already reject the reality of species. Perhaps that explains this book.

The biological species concept (BSC), used by nearly all evolutionists, including me, is based on reproduction: a species consists of a group of populations whose members can exchange genes with each other, but cannot exchange genes with members of different species—where the different species live in the same area in nature—because there are barriers that impede genetic exchange between different species.

Now the entire first chapter of our book Speciation, by Coyne and Orr, is a defense of the BSC, a discussion of its problems (no, it’s not perfect), and an argument that it’s superior to all other species concepts because it gives us a handle on why organisms in nature don’t form a spectrum (see the Appendix for a discussion of alternative species concepts, including “lineage concepts” mentioned by Mishler).

First, the question of whether species are “real” is the same as the question “is nature a continuum or lumpy?”. That is, when we look at organisms like mammals or birds or trees in one place, do we see a continuum of variation that we can partition only subjectively, or are there discrete entities that are recognized widely as distinct? And for nearly all groups of sexually reproducing organisms, nature is lumpy. You already know this if you try to identify birds or mammals or other sexually reproducing organisms in the wild. We don’t have a spectrum of birds but, in one area, you see a series of discrete types that you can easily identify. Those groups (in one area; see below) are biological species: robins, starlings, pigeons, etc. etc., and are formally recognized with Latin binomials.  They are real, and you or Joe or Jill can easily slot what you see into a small number of bird groups—species. The lumpiness of nature in one area is, in fact, THE “species problem”, the problem that, despite the title of his book, Darwin didn’t answer. (He didn’t answer it because he had no knowledge of genetics and therefore no concept of reproductive barriers.) We need to explain why, in one area, we see a number of discrete forms and no intermediates (or only a few, which could be hybrids that are often sterile.)

The answer to the species question is that reproductive barriers, which are many (we have a chapter on each type in Speciation), keep species distinct by preventing any blurring that would occur with gene flow. Though hybridization between species in one area is more common than we used to think, in most groups it is rare, and if the hybrids are sterile or inviable, then they pose no problem for “blurring” species boundaries.

Now some caveats, for the BSC isn’t perfect:

a.) The BSC is meant to apply to sexually reproducing organisms because it’s based on genetic exchange between individuals or the lack thereof. In organisms like bacteria that are largely asexual, you can’t use it easily. Now whether those organisms form clumps as discrete as those seen in sexually-reproducing species isn’t clear: few people are interested in that topic, which I think is important. This issue is discussed at the end of the first chapter of Speciation.

b.) Two groups must usually live in the same place if you are to determine with certainty whether they are members of different species. If they do not form hybrids that are viable and fertile where they co-occur, they are different species. This is true, for example, of the lion and tiger, which used to co-occur in India before the lion was extirpated. They formed no hybrids in nature. (They sometimes do in zoos, but that’s because captivity can eliminate some reproductive barriers that occur in nature, like aversion to mating with other species. I call this the “prison effect”).

c.) If two similar species live in different places, it’s hard to tell if they’re different species or simply different populations of the same species. If you bring them together in the zoo or lab and they do not hybridize, or form sterile or inviable hybrids, then they are different biological species. But if they do form hybrids, even some fertile ones, the question is still unresolved, for, as I said, some true biological species hybridize in captivity but not in the wild. One can only guess in such circumstances. This kind of guessing is what biologists do when they designate very similar populations that live in different areas as “subspecies”. The “zoo or lab” tests are one-way: they can tell you that populations living in different areas are members of different species, but can’t tell you for sure that they’re members of the same species.

d.) Speciation is a process, usually occurring between geographically isolated populations of a single species. With no possibility of gene exchange, these populations begin to genetically diverge due to various processes like natural selection, sexual selection (a subset of natural selection), genetic drift, and so on. If that divergence occurs to the point that, when the different populations re-establish geographical contact, they do not exchange genes, then full speciation has occurred. But it need not occur: there are many time when populations aren’t isolated long enough to become reproductively isolated, and in that case they can re-establish contact and exchange genes. Those are not members of different species. (This re-establishment of contact is why human populations did not evolve into different species.)

Or, there could be some reproductive isolation but it’s not complete. In such cases we have to make a judgment, like calling them “incipient species” or “groups with incomplete reproductive isolation.” It turns out that there are evolutionary processes that, upon re-contact of incompletely isolated populations, can drive them, though natural selection, to evolve into different and full biological species. One such process is called “reinforcement”, and it’s been seen to work in both nature and the lab.

The upshot is that because the evolution of one species into two or more is a continuous process, there will be stages of the process in which there is some reproductive isolation but it’s not complete. (Geographically isolated populations will, if left long enough, nearly always become full species). That means that there will sometimes be problems establishing whether two populations are species or not. I like to say that spatially isolated populations become more and more “species-like” with time, and, when reproductive isolation is complete, finally attain the status of full biological species.

e.) The reality of species is also seen by common sense (the value of bird guides, for example), by the remarkable coincidence between indigenous people and outside scientists in recognizing the same groups existing in one location, and through using statistical methods to see if individuals fall into discrete phenotypic or genetic clusters. This is the very first topic we take up in our book, and provide ample evidence that clustering in one area is real, and that the same clusters are identified by both local residents and biologists from outside the area, establishing that the clustering is not simply the result of humans subjectively partitioning a continuuum of nature into discrete units.

If you think that species aren’t real, go outside for half an hour and look at birds. If you know your birds, do they form a continuum, or does each bird you see fall neatly into a group that has been recognized, described, and written up in bird guides? You already know the answer. Bird species are real, and that’s true in other groups of plants and animals.

I could go on, but if you can get hold of Speciation by Coyne and Orr, I’d suggest reading Chapter 1, which gives evidence for the reality of species. Since our book was taken over by Oxford University Press, it’s now as expensive as the one above, so try to get it from a library. Chapter 1 is, I think, accessible to the scientifically interested layperson. (The book, however, is written for professional evolutionists: grad students, advanced undergrads, or professional evolutionary biologists. I always tell my friends not to read it unless they’re willing to slog through the stuff meant for professional evolutionists.)

So yes, species are real in sexually-reproducing organisms, but there are intermediate cases because it’s a process that takes a lot of time—evolutionary time. Finding cases that are hard to decide does not negate the value of the BSC, for, in the end, it’s the genetic barriers between species that allow them to continue diverging from each other without “pollution” by genes from other populations. In other words, it is the evolution of reproductive barriers that produces the lumpiness of nature that we see in one area.

And that is the great value of the BSC: it explains why nature is lumpy, a question that wasn’t answered by evolutionists until around 1935 or so. It answers the species question, at least in sexually-reproducing organisms.  The concept of genetic barriers (reproductive isolation) gives a natural explanation for nature’s lumpiness, and thus the question of “the origin of species” in sexually reproducing groups boils down to the question of “the origin of genetic barriers. And that gives us something to work with at last! How do those barriers arise, and what is their nature? As I wrote in Speciation, I don’t know of a single study on the origin of species of plants or animals in nature that is not about the origin of genetic barriers and reproductive isolation. That’s how pervasive and useful the BSC has been!

As for the “lineage concept” of species, it’s deeply confused, and you can read the Appendix of my book to understand why. Just one point here: what lineages are we talking about? Lineages of genes are different from lineages of populations, and those differ from lineages of biological species. Species concepts based on using lineages of genes, for example, always wind up in a big muddle, and have not been used to answer the question of why nature is “lumpy.”  Insofar as lineages are constrained to remain separate, it’s because they’re reproductively isolated! But read the book to see more. Or look at any intro text on evolutionary biology, like this one.

In short, yes, I agree that no species is better than any other, or has any kind of natural hegemony over other species. That idea is crazy, though of course humans do kill and eat members of other species. But that doesn’t mean that we’re better than, say, cows—any more than lions are “better” than gazelles. So here I agree with the book’s authors.

But I think their view that species aren’t real is deeply misguided. It is, I think, an example of what I call “the reverse appeal to nature.” This is what I call the tendency to impose onto nature your own ideological or biological prejudices. The regular philosophical “appeal to nature” is the misguided idea that “what is natural is good”. (It’s similar but not identical to the “naturalistic fallacy,” which is “what we see in nature is what we ought to do.”)

The reverse appeal to nature simply stands that appeal on its head, saying “what we think is good must be what occurs in nature.” Another example of is using ideology to deny that there are two sexes in nature because you have an ideology that maintains that biological sex is a spectrum. You must thus claim that what exists in nature must be what your ideology tells you exists. This is why we see the pervasive ideological denialism of what is a palpable truth recognized by biologists. (And yes, there are only two sexes in humans and other animals.)

Perhaps the ideology behind the “species are not real” claim is that if you don’t think there should be a hierarchy of species, you can simply deny that species exist. But you don’t have to deny the existence of species to be kind to animals.

If you have questions about species or speciation, I’ll try to read the comments within a day and answer them. Or, best, consult this: