Derek Turner writes . . .
A couple of weeks ago, I made a spontaneous decision to take the first-year students in my class on “The Meaning of Dinosaurs” on a ten-minute field trip to a special place in the Connecticut College Arboretum. We walked out across the road, past the student center. There, right next to a sidewalk between student center and the library, is an elegant metasequoia — a “dawn redwood.” We visited the tree to pay homage to a living fossil.
After having spent a couple of weeks reading and discussing papers about dinosaurs, I just had to show the students a tree that is, morphologically, barely distinguishable from trees that that flourished during the late Cretaceous and—in utter disregard of asteroids and/or cataclysmic volcanism—on into the Paleocene and Eocene. I can’t speak for any of my students, but for me it was kind of a special moment, aesthetically speaking. First of all, the tree itself is beautiful and stately, and quite unlike the hemlocks and hardwoods of Connecticut. Then there is also the joy of sharing with students some knowledge about a tree that many of them walk past every day. Most of all though, knowing that dinosaurs likely stood under trees just like this one drastically changes our aesthetic experience of the tree.
Suppose that a proposed expansion of the student center would require cutting down the metasequoia. I reckon I would work to protect that tree with indignation and gusto, in a way that I would never do for a run-of-the mill red maple. (Lorax, step aside!) There’s a sense in which I care more about the tree because it’s a living fossil, or because of what I know about the past. And I think that extra care might be reasonable, though explaining why is a philosophical challenge.
Did you know that metasequias are deciduous conifers? Photo by the author.
Fossil metasequoia from the Eocene (so, well after the time of the non-avian dinos), when the trees were extremely abundant. Image courtesy of Wikimedia.commons.
Trouble for the Living Fossil Concept
Lately, though, the notion of a living fossil has fallen on hard times. This well intentioned “educational” video from the PBS Eons series reflects a widely (though not universally) shared skepticism about the very idea of a living fossil. In recent years, a number of important studies (like this one or this one) have raised doubts about whether paradigmatic living fossil taxa deserve to be considered living fossils at all. If we were wrong about those paradigm cases like coelacanths and cycads, that might indicate that there is something irretrievably messed up about the very notion of a living fossil.
I sometimes wonder if one of the things that makes scientists so wary of talking about living fossils is that creationists have been known to misappropriate the concept. If you do a little browsing around the internet, you can find creationist sites that occasionally treat living fossils as evidence that evolution does not occur. Of course, this is badly mistaken in two ways: First, morphological stasis with respect to some fossilized traits is still compatible with a great deal of evolutionary change going on under the geological radar. Second, where it does occur, stasis itself is just an evolutionary pattern—an explanatory challenge, to be sure, but one that evolutionary theory has the resources to meet. We can explain stasis by invoking habitat tracking, stabilizing selection, developmental considerations, population structure, and even the differential extinction risk of ecological specialists vs. generalists. Living fossils therefore offer no aid or comfort whatsoever to the creationist. Still, I wonder if some scientists might judge that it’s easier to declare ‘living fossil’ an illegitimate concept than to continue deploying it while also taking countermeasures against misunderstanding and misappropriation. Although I can understand this impulse, part of me feels like it concedes too much. The fact that some people misappropriate or misunderstand a scientific concept does not seem like a good reason to jettison that concept if there are ways of putting it to productive work.
In this context, Scott Lidgard and Alan Love’s contribution last month is extremely welcome. If you haven’t already read their essay, check it out! Also, here is the more technical, peer-reviewed version of their argument. I join them enthusiastically in their effort to rehabilitate the living fossil concept. My goal here, though, is to build on their argument by bringing something into play that they leave out: The living fossil concept has an easily overlooked normative dimension. The lesson of the metasequoia moment is that calling something a ‘living fossil’ means saying something about its value.
From “Definitional Debates” to an “Integrated Agenda for Research”
Lidgard and Love argue that there are two very different sorts of cognitive work that we might ask concepts such as “living fossil” to do.
On the one hand, we might want the concept to do the work of classification. Some taxa are living fossil taxa. Others aren’t. And what we need is a set of criteria for distinguishing the living fossils from the rest. The problem, however, is that there are quite a number of different criteria associated with the term, and different scientists seem to apply different standards in different cases, resulting in unproductive “definitional debates.” Lidgard and Love argue that the widely shared worries about the legitimacy of the living fossil concept derive from pessimism about whether it will ever be able to do this first sort of work effectively.
More constructively, Lidgard and Love suggest that “the living fossil concept can be understood as setting an integrated agenda for research.” The different criteria for living fossil-hood can be reinterpreted as picking out phenomena that stand in need of explanation, and as fixing explanatory expectations. Rather than worrying so much about whether some taxon “really” does or doesn’t count as a living fossil, according to some contested definition, it would be far more productive, research-wise, to use the criteria associated with the living fossil concept to help guide and structure ongoing investigation. Thus, the second type of work that the living fossil concept might do (messy though it may be) is forward-looking and pragmatic. And unlike the first, this is a type of work to which the concept is well suited.
The Missing Normative Dimension
There are only two species of coelacanth in existence, both belonging to the genus Latimeria. One lives in the Indian Ocean, of the eastern coast of South Africa, while the other lives in Indonesian waters. The South African coelacanths are few in number, and highly endangered. What should we think if a corporation proposed to drill for oil in their habitat? (This is not hypothetical.) Perhaps coelacanths should be given relatively high priority for conservation because they are living fossils. Perhaps being a living fossil confers some value. But why exactly should this be so?
One plausible answer is that we care about phylogenetic diversity or evolutionary distinctiveness.[1] Phylogenetic diversity is a way of thinking about biodiversity that goes beyond merely counting species. The rough idea is that we should care about how much of the tree of life is represented in an ecosystem. Suppose, for example, that we have an ecosystem with four species of beetles. Now consider two possible interventions we could make:
(1) introduce another species of beetle that’s closely related to the ones already there.
(2) introduce a species of dragonfly.
Both interventions have the same impact on biodiversity, understood as mere species richness, since both bring the species count in our ecosystem to five. Now we might say that that (2) adds more diversity—in some sense—than (1). But in that case, we are essentially saying that there is more to biodiversity than mere species richness. Something else matters, too. And one possibility is that the something else has to do with genealogy.[2]
Suppose I am having dinner with my parents. We could invite my brother along, or we could invite my cousin. Either way, we will be a party of four. But if we invite my cousin, there is a sense in which our group will be more diverse, for it will encompass a broader swath of the family tree.
Is there any deep reason why we should care about phylogenetic diversity? I’m not sure it’s possible to tell any terribly compelling ethical story (whether ecocentric, biocentric, or anthropocentric) about the value of phylogenetic diversity. That is, it’s hard to see why (2) should be better than (1) in an ethical sense. (2) does not make for less suffering, or injustice, or frustration of the interests of living things, or whatever. But (2) could well be preferable on aesthetic grounds. The difference between (1) and (2) is chiefly historical and genealogical, and I’ve argued in an earlier post that history matters to aesthetic value.
With all of this in mind, here is a quick argument:
P1. Phylogenetic diversity has aesthetic value.
P2. Living fossil taxa contribute to phylogenetic diversity.
C. The extinction of a living fossil taxon would therefore mean the loss of aesthetic value.
P1 has some plausibility. But what about P2? Some of the paradigmatic living fossil taxa pretty obviously contribute to phylogenetic diversity. This is certainly the case with coelacanths and horseshoe crabs. (The latter, incidentally, are also threatened by human activity.) The coelacanths, for example, are probably more closely related to us than they are to other familiar ray-finned fish. And we would have to trace their evolutionary history way back to the Devonian, some 400-390 million years ago, to find an ancestor that they share with any other living species. Not all of the criteria for living fossil-hood that Lidgard and Love discuss have to do with phylogenetic diversity. The point is just that we can scarcely help but bring our own normative aesthetic interests to the study of living fossils.
These reflections suggest that Lidgard and Love’s rethink of the living fossil concept should be carried even further. They focus exclusively on the concept’s importance to empirical scientific investigation. But the concept may also pick out taxa that we think should be prioritized (on historical/aesthetic grounds) for conservation. The different criteria for living fossil-hood that Lidgard and Love consider might do much more than fix explanatory expectations or help to pick out evolutionary phenomena that need explaining. They also express different normative aesthetic interests that have relevance to conservation biology.
[1]For an extremely clear and helpful introduction to this idea, see James Maclaurin and Kim Sterelny, What is Biological Diversity?University of Chicago Press, 2008, pp. 135-142.
[2]The thought experiment isn’t perfect, because the dragonfly adds other kinds of diversity as well. For example, it adds to the morphological disparity of the system.