Interview Transcript

An Interview with Dr. Niles Eldredge, Paleontologist and Curator of Darwin

Q: Could you explain what Darwin meant when he wrote about how the fossil record in thick formations could be a good objection to his theory of evolution?

Darwin's theory of evolution through natural selection made him think that evolution would be progressive: going on constantly, very slowly and gradually through time. And so he was troubled. He said that we should find some change in geological formations--especially if they're thick--from the bottom of the pile to the top of the pile, to record this gradual change. And he said: If we don't, it's a good objection to my theory.

Q: Could you explain what Darwin meant when he wrote the note, "If species really, after catastrophes, created in showers world over, my theory false"? Did Darwin think of extinction events to be a hindrance to his theory? Was his theory false? Why not?

It turns out that the rock record shows that species are very stable--often for millions of years. They don't show a lot of evolutionary change. But his theory's not false. It's just that most evolutionary change occurs in relatively rapid bursts--5 or 50,000 years--rather than millions of years, where they're typically stable.

So his theory's not false--it's just a special form that he wrote that theory. He insisted that it must be slow, steady, gradual change--progressive through time. And when he saw that this wasn't the case, he blamed the fossil record. He said: The fossil record is faulty.

It turns out the fossil record was great, and it shows what happens over millions of years--and very often species remain stable for millions of years. And when evolution then happens, it happens over 50,000 years; 100,000 years. That's rapid geologically--it's not rapid ... too rapid for evolution to occur, though. And natural selection can move and change the adaptations of species in these sudden spurts.

Q: How does your work contradict that? Do species change much over time?

Evolution, it turns out, happens--can happen very rapidly. A couple of thousand years is often enough to establish a new species. And this seems to be the norm, rather than the kind of picture that Darwin painted--of slow, steady, gradual change through time. It's just rapid periods of change that interrupt these longer--much longer--periods of relative stability.

What we see in the fossil record is that evolution happens in rapid bursts.

Q: How does environmental stress play into evolutionary processes?

Environmental stress is the key to understanding how evolution works. It's how old species are driven to extinction, and it's also the reason why new species evolve--come into being.

Those observations seemed, to him, to contradict his picture of slow, steady, gradual change.

Darwin knew about extinctions. It wasn't extinction that bothered him--it was the sudden appearance of many new species after an extinction event.

But now we know that that's a common--That was a commonplace kind of event. Most evolution seems to be correlated with extinction events. And disruption of ecosystems driving old species extinct--many old species extinct--and causing new species to evolve, almost at the same time.

Q: What is Punctuated Equilibria?

Punctuated equilibria is an idea that I published with Steve Gould in the early 1970s. What it says is that the fossil record is giving us a true signal--that species don't change very much, often for millions of years. And when evolutionary change occurs, and new species arise from old ones, it can happen relatively quickly. And that this is a common pattern in the history of life.

Q: What do you primarily study to support this theory?

Everybody needs a group to become an expert in to study evolution. Darwin picked pigeons, to understand how artificial selection, for example, works. My group was trilobites.

Q: What is a trilobite?

They're a group of fossil creatures that first appeared about 540 million years ago and became extinct about 245 million years ago. They're relatives of lobsters, and crabs and shrimp--things like that. The group that I studied was in the middle of the Devonian Period--in the old seaways that ran from New York all the way out to Iowa, leaving a beautiful fossil record over about 8 million years in time, starting about 380 million years ago.

Q: Why are trilobite's ideal subjects for your theory?

Trilobites are abundant fossils. They are the only kind of fossil--even I would include dinosaurs--that actually look like animals. They've got eyes, and they got bodies, and they're very complicated. So their complex anatomy gives you a chance of detecting evolutionary change.

Q: So what do you think of Darwin?

I'm a big fan of Charles Darwin, and a big supporter of his theory of evolution. But, ironically, my entire career has been devoted to showing the few places where he went astray.