Between Extinctions
An interview with Niles Eldredge

Paleontologist Niles Eldredge entered the world stage in 1972 when, together with his colleague Stephen Jay Gould, he proposed the concept of punctuated equilibrium to explain the pace of evolutionary change. Eldredge and Gould pointed to the rich but irregular fossil record as evidence against the traditional view of evolution as a gradual and incremental process. What had been perceived as missing fossil information, they suggested, represented valid data about how evolution proceeds.

Punctuated equilibrium portrays evolution as a protracted saga with only intermittent action. Species pass through long periods of little or no change, called stasis, interspersed with punctuated events precipitated by mass extinctions and followed by the rapid origin and diversification of new species. The theory has had a mixed reaction from scientists, and Eldredge continues to provoke active academic debate.

Eldredge is the author of several popular books, among them, Dominion, The Miner's Canary, and The Monkey Business: A Scientist Looks at Creationism. His most recent book, Life in the Balance, has just been published by Princeton University Press, in conjunction with the opening of the Hall of Biodiversity at the American Museum of Natural History in New York City, where he is curator in the Department of Invertebrates.

California Wild: It's been about 25 years since you and Stephen Jay Gould first published on punctuated equilibrium. Many gradualists describe the debate as over and so do many punctuationists, and both say it was decided in their favor. From your perspective, has the dust settled at all?

Niles Eldredge: I think that, empirically, stasis is a clear phenomenon. It was really a rediscovery of something that was known in the nineteenth century, and most paleontologists agree that the fossil record shows great stability of most species. People like [evolutionary biologists] Richard Dawkins, George Williams, and John Maynard Smith all agree that stasis is a real phenomenon. There might be some diehard gradualists who don't see it that way, but I think the dust has settled.

CW: How then do they make theories of constant genetic mutation and natural selection fit the empirical evidence for long periods of stasis?

NE: Well, they say we've known all along that evolution proceeds at variable rates. There's nothing really new, and we don't need new evolutionary mechanisms or paradigms to embrace that. At one sort of simple level, that's certainly correct.

CW: So stasis can be explained in terms of gradual natural selection?

NE: Actually, George Williams said that stasis is real, it's important. We should have seen it earlier, but Eldredge and Gould are not positioned to tell us anything intelligent about how it occurs or why it occurs. I think just the reverse. I think that there's not only the acceptance of stasis but there's a fairly good understanding of why stability occurs. It was natural for people to assume that when environments change, the genetic variations within species will track the changes, and populations will change or diverge.

CW: Evolve or Die?

NE: Yes, that kind of thing. The rejoinder to that is if you look at the Pleistocene history of North America or Eurasia, you'll see that environmental change is caused mostly by climate change. The ice comes down, the tundra comes down ahead of it and so does the boreal forest and the mixed hardwood forest, and so on. Everything collapses to the south. It turns out there's not a lot of extinction going on and very, very little evolution. What's really going on is that species are just staying alive by tracking familiar habitat.

CW: They're just moving.

NE: As long as you can find the stuff you've already adapted to, it doesn't matter where you are. There were lions in Trafalgar Square. To me that is a very appealing explanation for stasis. Though it's counterintuitive, it's clear there's stability in the face of environmental change. Stabilizing selection still is the predictive norm.

I'm continually frustrated by modern geneticists thinking of species as simply large populations and seeing no distinction between the species, on the one hand, and local populations of conspecifics integrated into the local ecosystems. If you look at what Sewell Wright was doing in the early thirties, he had this model of species being broken up into local populations, called demes, having a semi-independent history of selection and mutation. And you just add the notion that each one of them is living in slightly different circumstances, with slightly different food resources, predators, disease perhaps, and so forth.

I'm an easterner, so I'm familiar with blue jays. They go from New Jersey and Maine all the way over to the Rocky Mountains, living in a whole bunch of different ecosystems. It's impossible for me to imagine a selection pressure of any sort, whether it arises from the rest of the biota or some physical thing, affecting all of those populations in precisely the same manner and having them respond in precisely the same manner as well. Anybody who took Sewell Wright seriously would have realized that natural selection will act slightly differently on each of the local populations of a species. The probability that an entire species will slowly evolve in any one single direction is thus very, very low.

I find that population geneticists are harder to talk to than molecular people. At least molecular people know that they're dealing on one level and we're dealing on another. I think the population people feel they inherited the mantle of evolutionary theory and are bothered by molecular people and paleontologists.

My big difference with Dawkins is that he's saying that the competition for reproductive success is the thing driving evolution. And if somebody like me comes along and says "Well what about Cretaceous meteor showers?" he responds, "Stuff happens," and says that the whole system will adjust. What Gould and I are saying is that a pattern runs at various levels, from the species and ecosystem level on up to the global level. That pattern absolutely permeates the history of life for the last 535 million years, and there is no change until something comes along to really knock things out of whack.

I have no problem with natural selection being the essential engine for the change. The question is, who's driving the car? Who's navigating through the streets of earth history? It seems to me the engine is basically guided by these extraneous physical environmental effects.

CW: How far do you want to push that analogy? You wouldn't want to posit that the car has a driver, would you?

NE: No. I'm saying something external to the engine is driving it.

CW: But an unintentional driver.

NE: You're right.

CW: And that something is what you propose in species selection or are there other mechanisms?

NE: No, I'm much more interested in cross-genealogical patterns of stability and disruption of ecosystems. I think that's the key. I'm looking at physical environmental effects--mostly global cooling events, or meteors smacking into the Earth, or continental movements. The rise of the Panamanian Isthmus caused a great deal of faunal interchange. It changed the physical environment of the seaway and the Appalachian Basin.

CW: But other than these large external processes, must there be some other forces responsible for macroevolution?

NE: I'm not too big a fan of that stuff anymore. I think the rhetoric has got to switch over to ecosystemic influences. I've got to sit down and rethink adaptive radiation [the rapid diversification and spread of several closely related species from a single ancestor] and some of the other classic genealogical patterns that are out there.

I was never much of a fan of species selection [a hypothetical process for how successful species rapidly displace their ancestors]. I was persuaded more by [paleontologist Elisabeth] Vrba's work that lower-level causality can explain those kinds of patterns, differential production and deaths of species based on intrinsic properties of organisms and so forth. There's no question there are differential patterns of evolution and survival of species within lineages. But I think there are problems with calling that "selection."

CW: In Dominion you talk about the importance of stories, and of course the story of the evolution of life is a powerful and interesting one. How do you see punctuation modifying how that story is told?

NE: Darwin's argument succeeded because he explicitly tied evolution to the idea of progress, at a time when progress was emerging as a good thing. But there's nothing written into the system that says it's going to progress. Indeed, stability is the norm. I believe that the dinosaurs would still be here if they didn't accidentally get knocked off. But there's no need to say intelligent dinosaurs would have evolved.

CW: How do stasis, or non-progress, or punctuation relate to your predictions about how evolution will be affected by the extinctions we're experiencing now?

NE: That's interesting. Conservation biologists run around saying, "My God, losing all this genetic diversity is going to put a crimp on evolution." Of course, just the opposite is the case. I don't see much evolution happening unless and until you've had one of these events. But the extinction process has got to stop before evolution will kick in.

CW: Could you say a little bit more about that? What is the evidence in the fossil record?

NE: It's the lag. Climate does rebound, or things take five or six million years to get used to a lower temperature regime or whatever it might be. With a meteorite it's literally the dust settling. [Conservation biologist] Michael Soule says, as long as you continue to disrupt an ecosystem, it's not going to recover, and if it's a large-scale disruption, then part of the recovery entails the evolution of new species. In this case we are the vector of the extinction. And evolution is not going to kick in until we stop doing what we're doing.

CW: Maybe it's not "we" who are the vector, but it's some attribute of ours that's the vector. Perhaps it's possible to suppress that attribute without removing ourselves entirely.

NE: Yes. That's right. It's our sheer numbers and the disproportionate consumption and distribution of wealth that's doing it. Perhaps these things can be addressed without the cessation of human life. Not that I'm calling for going back and trying to live as hunter-gatherers.

CW: I haven't yet met a New Yorker who's called for that.

NE: Exactly. In the case of humans, cultural extinction usually precedes biological extinction. We are losing all that cultural diversity as we're going along. Eventually we'll be at risk from our activities. Famine, warfare, and disease are direct by-products of overpopulation, and the disproportionate distribution and consumption of resources are the real specters that are haunting us.

CW: You talk in your book about the distinction between cultural evolution and biological evolution and seem to create a pretty effective clutch between those two. They're related, but distantly so.

NE: Cultural evolution has always proceeded a lot faster than biological evolution. Today you can learn it from the Internet. You're not just getting your genetic information from your parents, you're getting all kinds of cultural information transmitted laterally. I'm a collector of Victorian cornets, and I'm very interested in their evolution. I've tried to come up with a simple classification of cornet diversity and couldn't do it. The reason is because there's no simple genealogical system; there's so much lateral transmission and theft of ideas.

CW: You don't have to steal from your own lineage.

NE: Yes. There were a couple of basic very successful models developed, and people just copied them.

CW: Could the Internet possibly homogenize humanity and, in the process, create a sort of overall species sense of survival?

NE: There's something that is unique to humans that people have ignored. It happened 10,000 years ago when we invented agriculture and became the first species whose local populations were no longer living inside local ecosystems. By doing so we, in effect, stopped natural selection for the time being. I was reading in Paul Kennedy's Preparing for the Twenty-first Century that human beings exchange one trillion dollars worth of goods and services globally a day, and this was five-year-old data. If we can get a little more explicit about recognizing that we are a concerted force, the Internet could become a way of communicating that more broadly throughout the biosphere.

CW: Soule and other conservation biologists talk about the stabilizing effect of diversity in an ecosystem, suggesting that the more diverse ecosystems tend to have greater stability. I wonder if the same is true for culture.

NE: It depends on the history of the systems you're looking at. Finland was very homogenous and pretty darn stable. Then the Swedes came and the signposts had to be in two different languages. Now that other immigrants are coming in there's some instability injected. This business about stability confused the hell out of the editor of a book that I'm writing in conjunction with the opening of our new biodiversity hall [at the American Museum of Natural History]. He was sending me tons of articles in the ecological literature precisely to the point that you are asking.

I wouldn't automatically think that a tropical rainforest ecosystem or a coral reef ecosystem is intrinsically more stable than the tundra or some other much more simple system. So I don't know if I even buy into the premise. If it were so, then a tropical rainforest somehow is intrinsically more important than the tundra. There are more different things there, and if we're worried about having those and saving everything, which in a sense we are, then maybe from that point of view it is more important. But otherwise, how could you possibly say such a thing?

I'm more intrigued by biomass considerations. Apparently there's as much biomass per square hectare in the tundra as there is in the tropical rainforest. It's just distributed differently. Is a tundra more fragile than a tropical rainforest? They're both very fragile today.

CW: If diversity doesn't contribute to stability, why do we care so much about it? We acknowledge that its reduction is horrible, that it's a tragedy, but we can't exactly explain why.

NE: I just wrote an essay to be published in Natural History along with the opening of the new hall. The managing editor said, "It's not even the question of "Why should we care?" it's "Why don't we?"' An awful lot of people don't. I think we don't care because for 10,000 years we have not been living within ecosystems and so we think we just aren't part of nature the way everything else is. The "Dominion" passage in the Bible reflects that, and I think it's accurate. And we've gotten away with it. There have been no real consequences aside from an occasional famine. We're wildly successful from that point of view. That's why we don't care. But, while we're not inside local ecosystems we are inside a global system. I was going to say "trapped," but that's the wrong word.

The United Nations predicts that we're going to stabilize the population at twelve to fourteen billion. The limitations are not just agricultural limitations; they are limitations of what the Earth can support in terms of the ecosystem--the cycling of carbon and nitrogen and the production of oxygen and fresh water. As we approach the limits of the Earth, we have to redefine our position in the natural world.

The second argument is that we are utilizing 40,000 or so species globally a day, mostly plants. Medicines and agriculture still hugely depend on the diversity of the living world. We don't even know what's out there yet.

And then there is the ethical, esthetic sense which, without going all the way into E.O. Wilson's philosophy [of biophilia], is in our genes--though most of the people in Brooklyn are homozygous recessive. His argument is dicey, but I know what he means, and intuitively I think that people do know that they're animals and do like fresh air, green grass, forests.

CW: Changing gears for a moment, I know some creationists, one of whom actually cites your work and Gould's work as evidence for special creation theory. He says, "That all of these phyla appeared six hundred million years ago and haven't really changed much since then is not a mystery. That's when God chose to create the phyla." How does it feel to be used as ammunition marshaled against evolutionists by creationists? And what do you say to creationists when they say, "Stasis is not necessarily proof of creation theory, but it's certainly evidence in favor of its basic tenets."?

NE: We got dragged into this in the early '80s by a guy named Luther Sunderland, who's now dead. He was an engineer for General Electric, did a lot of the engineering for the B-1 bombers. The guy was not dumb. But he was the leading creationist on the East Coast. I didn't know that when he came to me representing himself as a consultant for the New York State Board of Regents, who are the people who oversee the curriculum for high schools. When I got the typescript back he had me responding to, "So you don't mind seeing Creationism taught side by side with evolution in the public schools," saying, "No, I think it's good." What I really said was that I don't mind a science teacher starting off by saying there are other explanations for this, but they're mostly in religious traditions, not in the scientific tradition.

He invited me to change anything I wanted to, so I did. But by that time, he had already introduced that transcript into a study session of the Iowa State Legislature. Later on I became friendly with Sunderland and would go on TV with him. The other thing was that Sunderland got to President Reagan's speechwriters because of punctuated equilibrium. Reagan went to a convention of fundamentalist ministers in Texas and attacked evolution saying that "It's a scientific theory only, and it has in recent years been challenged in the world of science and is not yet believed in the scientific community to be as infallible as it once was believed."

My position is the same as Darwin's on this: Evolution works through processes such as natural selection and speciation. If someone wanted to say that life started three and a half billion years ago with bacteria, then God saw to it, using natural processes such as evolution, that other things would come along, including the Cambrian explosion, I would have absolutely no problem with that. But not if he says that Darwin said evolution is slow and gradual; Eldredge and Gould say it proceeds by fits and starts. Ergo Eldredge and Gould don't believe in evolution.

Evolution is the idea that all organisms descended from a single common ancestor. Period. Though we can argue about mechanisms, I have no doubt that selection and speciation are the heart and soul of the evolutionary process.

CW: You pointed earlier to the origin of agriculture being the time when we first defined ourselves as a unique species by stepping out of local ecosystems. The human form in its modern manifestation has been around one or two hundred thousand years, yet modern behavior doesn't seem to start appearing until about 50,000 years ago. When do you think that culture first began to eclipse biological evolution?

NE: About 2.5 million years ago there was a climatically induced turnover [of species in Africa], and at the same time the development of the first stone tools. Since then, humans have shown less and less direct response to weather change and more and more to their material culture. In his new book, Becoming Human, my friend Ian Tattersall says that these behavioral innovations very quickly become decoupled from speciation events. Homo sapiens begin to wander around the globe starting 100,000 years ago. But there's no creative spark, such as art, until about 30,000 or 35,000 years ago. There are some problems with the dates now in Australia, but certainly in Europe that's very well tied down. And that's not a biological event, that's something else. Something profound did occur starting about 30,000 years ago.

CW: You could say that's when culture became the primary influence on our behavior rather than environmental change?

NE: No, I wouldn't actually say that. That had happened long before. It's things like music and art that have less obviously practical uses. It's when the human spirit comes in.

CW: Human spirit is a difficult thing for a paleontologist to study.

NE: Yes. Well, it does have its manifestations, like cave paintings. Tattersall was reminding me that about 30 years ago, archeologists had found lots of pollen grains in an Iraqi Neandertal burial. They were probably from flowers being placed into the grave, which, again, may be some sort of an inkling of awareness, a manifestation of the human spirit.

sum 98 cover

Summer 1998

Vol. 51:3