From the War of Nature

Derek Turner writes . . .

What if our representations of dinosaurs sometimes say more about us than about the animals themselves?

Why, for example, do we so frequently represent dinosaurs as fighting? One classic example of this is Charles Knight’s famous painting of the gladiatorial face-off between Triceratops and Tyrannosaurus rex.

T. rex couldn’t really box, but look at how the animals are squaring off like prizefighters on opposite sides of the ring. Or like cowboys facing off at high noon. We’re looking at dinosaurs, but the ritual being enacted here is familiar. And human. I observed many fights when I was in junior high school, and every single one of them started with a ritualized face-off, just like this. Or like this:

The trouble (as Brian Switek explains here), is that there is not a shred of evidence that such duels ever actually happened. That bears repeating: THERE IS NO EVIDENCE THAT TRICERATOPS EVER ENGAGED IN COMBAT WITH T. REX. There are a few suggestive tooth marks in Ceratopsian frills, but toothmarks do not necessarily imply combat, since they could easily have been made post-mortem.

None of this is to say that representations of T. rex fighting Triceratops are inaccurate. The point is that such representations are only loosely constrained by the empirical evidence. Even as our understanding of dinosaurs has changed a great deal, certain ways of representing them have remained deeply entrenched. For example, this was the cover of a book that was one of my own favorites, when I was a kid:

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But even as scientists like Robert Bakker led the dinosaur renaissance in the 1980s, the dueling dinosaur motif persisted.

Seen in historical context, there is nothing terribly heretical about the depiction of dinosaurs fighting.               

Prehistory as a Mirror for Humanity

The evidential slack means that that there is room for us to read our own human foibles and predilections back into nature. We reconstruct prehistoric life—and dinosaurs in particular—in our own violent image.

In an earlier post, I suggested that part of what draws us back to the Mesozoic is nostalgia for a wilder world where humans have no place. But we also populate that wilder world with animals that can seem a lot like us, animals that wasted their time on Earth in perpetual conflict and combat. My claim is that representations of prehistoric life can function as a mirror that shows us something about ourselves, if obscurely.

Recently on a visit to Yale’s Peabody Museum of Natural History, I saw a (quite famous) dinosaur skeleton that, amazingly, drove both of these points home at the same time. It was Deinonychus—a specimen that, interpreted by John Ostrom, helped to launch the dinosaur renaissance. But there's poetry in the decisions about how to mount the skeleton:


The animal is pouncing, in the middle of an attack. The dynamic pose contrasts with earlier representations of dinosaurs as sluggish, such as Knight’s painting. But combat is the common thread. Why not portray Deinonychus as sitting, or napping? Many predators spend most of their time lazing around. One part of the answer is that we like to watch violence. Another part of the answer is that we like being told that our own violent tendencies are natural.

What is Deinonychus pouncing on? You! The museumgoer. Even though it’s just a skeleton suspended from the ceiling, the museum exhibit places you, the visitor, in the wilderness before time, where animals like Deinonychus might leap at you and eat you. The exhibit places you in a fight with a dinosaur, and one that you are guaranteed to lose. There is a fascinating double movement here: the exhibit cuts humanity down to size, but the animal doing the slashing is strangely humanized. It is using its weapons to attack you in the way another person might do.

Dinosaur Weaponology

This obsession with dinosaur fighting also, I suggest, has some impact on paleontological research. A lot of work goes into the functional morphology of dinosaur weapons. Consider the thick cranial domes of some pachycephalosaurs. In the dinosaur books I loved as a kid, the animals were often portrayed like this:


These, presumably, are males, ramming each other into submission to see who gets the territory, or the females. The thick skulls evolved by sexual selection. Or so the story goes.

Along the way, however, some scientists have expressed skepticism about this picture. For example, Kenneth Carpenter argued (here) that the tops of pachycephalosaur skulls have too little contact area for the head butting to work. Instead, he hypothesized that the animals must have engaged in "flank butting." Others have wondered about the morphology of pachycephalosaur necks. Was the curvature of the neck vertebrae well designed for withstanding impacts? Perhaps the skulls were instead used for display or recognition. Meanwhile, other researchers have looked at pathologies--at the frequency of bone lesions in pachycephalosaur skulls--and argued that those are suggestive of injuries due to head-butting. Debates about the head-butting hypothesis have also gotten plenty of public attention.

My worry about all this is not that the head-butting hypothesis is wrong. My worry is just that there is so much attention lavished on research on dinosaur weapons--and on what are thought to have been male weapons, at that. There are lots of interesting questions that could be asked about pachycephalosaurs--about their ecology, about other aspects of their behavior--and yet it almost seems like the only thing we see when we look at the animals are their weapons. When dinosaur weaponology research gets disproportionate public attention, that creates the impression that the weapons were their most important features. Indeed, we often treat dinosaurs' weapons and armor as their defining features. But there's no deep reason why we have to do that.

Stereotypes about Dinosaurs?

We also represent dinosaurs in a way that showcases their weapons. If you take time to observe carnivores—your pet dog counts, as do the backyard coyotes—you might notice that they do not spend much time with their mouths hanging open. If we wanted to, we could adopt a practice of always portraying dogs like this:


But this would be a kind of reputational injustice to dogs. The representation isn’t exactly wrong—dogs do sometimes act like this—but it’s biased. Just try, however, to find a museum exhibit in which a carnivorous dinosaur is reconstructed with its mouth closed.

There are interesting cases where people have messed up stereotypes about other animals. (Actually, these can interact in complex ways with stereotypes about people. These are complicated issues, but this book by Vicki Hearne might be one place to start exploring them.) For example, many people think of pit bulls as especially ferocious and aggressive dogs. But people who’ve hung out with snuggly, well cared for pit bulls know otherwise. It's not even entirely clear what breed, if any, the term "pit bull" is supposed to pick out. They are just dogs. Perhaps we are guilty of stereotyping dinosaurs in somewhat the same way.

From the War of Nature

This tendency to read of our own interests and predilections back into nature is nothing new. Darwin did the same thing. Many people have cited the famous closing sentence of the Origin of Species, the one that opens with, “There is a grandeur in this view of life . . .” For many years, Stephen Jay Gould wrote essays for Natural History magazine under the heading, “This View of Life.” However, the sentence that precedes the famous closing line is just as revealing--and, I would argue, kind of problematic. Here it is:

“Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows”

(p. 425. All page numbers are from this version of the Origin, which is available online.) 

Nor is this the only place where Darwin uses war and battle as metaphors. In his chapter on the struggle for existence, he writes that “battle within battle must ever be recurring with varying success . . .” (p. 71). In the discussion of sexual selection, he refers to “the law of battle,” according to which males of most species must use their “weapons” to fight for access to females (p. 84). Remember the pachycephalosaurs.

Just to be clear: there is absolutely nothing in the theory of natural selection that obligates us to think of it as involving war, or combat, or fighting. In familiar schematic form, all you need for natural selection is heritable variation in a population that makes some difference to survival or reproductive success. Darwin’s line about the “war of nature” is gratuitous. So why is it there? Of course predation is violent. But war and battle are, in the first instance, human activities. These metaphors are optional.

Darwin’s penultimate line looks a lot like theodicy. The war of nature is horrible and gruesome, but maybe it’s justified by its results—the “most exalted object which we are capable of conceiving.” Of course, that most exalted object is us. So our own human activity—war—is made to seem natural, because that’s what all other creatures have been doing all along anyway. But the war of nature is then supposed to be justified by the fact that it has produced “higher animals” like us that make war with each other.

It’s hard to see the grandeur in this view of things.

Further Reading

This post builds on some ideas about war as a metaphor that I developed in an earlier paper. There may also be a connection between seeing nature as a scene of constant warfare, and seeing ourselves as being at war with nature. 



Artificial Species Selection

Derek Turner writes . . .

Earlier this year, Joyce and I had some conversation about species selection (here and here). More recently, Leonard pointed out that Buffon may have anticipated the idea of species selection (here). This week, I thought I'd return to the topic and explain why I think species selection is such an important idea.

Species Selection: What is it?

Species selection occurs when the following conditions are met:

(1) There is differential persistence, extinction, and speciation (or branching) of whole lineages, or species, in evolutionary history.

(2) That process is not completely random. Instead, there is something about the species that affects their probabilities of persisting, going extinct, or speciating. In other words, you have differential fitness at the level of whole species.

(3) Whatever it is about the species in question that makes for differential fitness gets transmitted via speciation. So if species A gives rise to species B via ordinary speciation processes, features of A that increase (or decrease) extinction risk, say, will get passed on to B.

In other words, you need heritable variation in fitness at the level of whole species. In addition to these three conditions, some theorists think we need more than this for bona fide species selection:

(4) The traits of species that make the difference to their probabilities of extinction, persistence, and speciation, must be emergent traits. It’s not enough if those traits are merely aggregates of the traits of individual organisms.

Condition (4) takes us rapidly into philosophical territory. What does ‘emergence’ mean? It’s easier to give an example of an aggregate (non-emergent) trait. Many theorists have thought that large body size increases extinction risk. So big-bodied species, such as your sauropod dinosaurs or your woolly mammoths, might have lower species-level fitness. The problem, though, is that average body size is merely an aggregate measure. When we say that woolly mammoths are big, we don’t mean that the species itself is big, but that its individual members have a large body size on average. So if all we required for species selection is conditions (1) through (3), then large body size could be a factor. But if we insist on condition (4), large body size won’t cut it, because the trait is not emergent in the right sort of way.

Does large body size increase extinction risk? Average body size of the species is merely an aggregate trait. Image courtesy of wikimedia commons.

Does large body size increase extinction risk? Average body size of the species is merely an aggregate trait. Image courtesy of wikimedia commons.

There are trade-offs here. If you take the broader view, insisting only on conditions (1) through (3), then species selection is somewhat easier to find in nature, but it may also turn out to be less interesting, theoretically. On the other hand, if you insist on condition (4), then it’s really interesting, theoretically—because of the strong anti-reductionist implications—but also much tougher to document in nature.

Species Selection: Why Should We Believe in It?

As an empirical matter, though, on either the broader or the narrower view, it can be very difficult to point to cases in evolutionary history where we really need to invoke species selection in order to explain some puzzling phenomenon. I’m not sure if there is a consensus view about this at all—everything about species selection is controversial—but it might be good to start with what I’ll call the Explanation of Last Resort View.

“Sure, species selection could happen in principle. But it’s hard to document in any clear way, and it seems like the usual population biological explanations, which invoke selection, drift, mutation, and migration, give us a lot of explanatory mileage. So as a rule, don’t invoke higher level mechanisms like species selection unless you absolutely have to.”

Perhaps many scientists would add that as a matter of fact, you hardly ever, if ever, really need to invoke species selection.

Those scientists who’ve made the most convincing cases for species selection so far, have turned to the fossil record. For example, David Jablonski (1987) has done some research showing that the geographic range size of marine invertebrates makes a difference to extinction risk.

Charles Darwin. Image courtesy of wikimedia commons.

Charles Darwin. Image courtesy of wikimedia commons.

But why not take a lesson here from Darwin, that virtuoso of argument construction? Famously, in the Origin, Darwin tried to soften up resistance to his theory of natural selection by starting out with artificial selection. His go to example was pigeons, since he thought we have pretty good evidence that domesticated pigeon breeds are all descended from a common ancestor. Darwin also knew that the breeds of pigeons—the pouters and tumblers and fantails—were so different from one another that a naïve naturalist might well classify them as different species. In this case, it’s entirely plausible that artificial selection is the source of those remarkable differences. Generations of breeders determined the reproductive fate of their pigeons. If you accept this story about pigeons, then Darwin’s claims about natural selection in wild populations seem rationally irresistible.

A jacobin pigeon. Image courtesy of wikimedia commons.

A jacobin pigeon. Image courtesy of wikimedia commons.

A pouter pigeon. Image courtesy of wikimedia commons.

A pouter pigeon. Image courtesy of wikimedia commons.

One important piece of Darwin’s argument was the observation that human breeders—the artificial selectors—often have little if any clear idea of what they are doing. Selection is sometimes “unconscious”:

Thus, a man who intends keeping pointers naturally tries to get as good dogs as he can, and afterwards breeds from his own best dogs, but he has no wish or expectation of permanently altering the breed. Nevertheless, I cannot doubt that this process, continued during centuries, would improve and modify any breed …

Breeders are not necessarily aiming at any particular target. They are just making their own (likely aesthetic, perhaps also utilitarian) judgments about which of their dogs are the best. It’s a small step from “unconscious” human selection to mindless natural selection.

Paleontology and Neontology

Now to lay my cards on the table: It seems to me that if one wanted to defend species selection, the obvious way to do it would be to start just as Darwin did, but with cases of artificial species selection. Are there cases in which human activities contribute to the differential survival, reproduction, and speciation of whole lineages? And note that following Darwin, there’s no need to suppose that the human selectors are fully cognizant of what they are doing. Darwin seems to use “artificial selection” in a very broad sense: although his examples all involve animal breeding, once you see what he says about unconscious selection, it’s hard to see why we should extend the term “artificial selection” to other cases. For example, human fishing has led to size decrease in many fish species. That’s not a case of domesticated animal breeding, but it still seems like artificial selection.

Does artificial species selection occur in nature? Over the last few centuries, human activities have contributed significantly to the differential persistence and extinction of lineages, much as Darwin’s pigeon fanciers contributed to the differential reproduction of their birds. Plant and animal species living on islands, for example, have fared very, very badly, as humans have arrived in place after place with cats, rats, mice, pigs, goats and other ecological troublemakers. Species on continental landmasses have tended to do better. Human activities have meant that island dwelling species have higher extinction risk. This sort of case clearly meets conditions (1) through (3) above, though perhaps not condition (4). The point, though, is that we can explain the extinction patterns by making high-level generalizations about the extinction risk associated with living on islands. And it's human activity that makes island-dwelling risky.

This notion of artificial species selection is not really new. In an important review paper on species selection research, David Jablonski (2008) wrote that “[t]oday’s biota appears to be in the midst of a massive experiment in strict-sense species selection” (p. 515). That seems right, although it would take more work to show that condition (4) is met in cases of artificial species selection. Species selection is real. It’s happening right now.

Why is this not totally obvious? I’ll conclude on a speculative note: In some of his recent contributions, Leonard has stressed some of the conceptual discontinuities between paleontology and neontology (here). Species selection theory is a product of the paleobiological revolution of the 1970s and 1980s. It was devised and defended by paleontologists (Steven Stanley, Stephen Jay Gould, Elisabeth Vrba, as well as the philosopher Elisabeth Lloyd), for the purpose of explaining the patterns of life’s history. The failure to recognize the obvious relevance of species selection theory to conservation biology seems like another instance of the all too familiar paleo/neo disconnect.


Darwin, C. (1859/1964), On The Origin of Species, A Facsimile of the First Edition. Harvard University Press.

Jablonski, D. (1987), "Heritability at the species level: analysis of geographic ranges of cretaceous mollusks," Science 238: 360-363.

Jablonski, D. (2008), "Species selection: Theory and data," Annual Review of Ecology and Systematics 39: 501-524.

The argument in this post is developed in greater detail here.