Big Thinkers on Evolution

Big Thinkers on Evolution

Note: Other than the clips for Sylvia Earle, all excerpts were drawn from interviews originally conducted for the Evolution series, which premiered in 2001. Sylvia Earle's interview was conducted in fall 2009.

Dan Dennett
Professor of Philosophy

NOVA: Why is Darwin's theory "the best idea anybody ever had"?

Dan Dennett: If I were to give a prize for the single best idea anybody ever had, I'd give it to Darwin for the idea of natural selection—ahead of Newton, ahead of Einstein—because his idea unites the two most disparate features of our universe: the world of purposeless, meaningless matter and motion, particles jostling on the one side, and the world of meaning and purpose, design on the other.

The traditional view of purpose says it comes from on high, from God, from the Creator. Darwin's idea of natural selection makes people uncomfortable because it reverses the direction of tradition. Whereas people used to think of meaning coming from on high and being ordained from the top down, now we have Darwin saying, "No, all of this design can happen, all of this purpose can emerge from the bottom up without any direction at all."

Now, in the end, we still have purpose, we still have meaning, we still have beauty and life itself. So everything is, in one sense, the same, but you're coming at it from a different direction. And that inversion, what one of Darwin's early critics called "a strange inversion of reasoning," is very upsetting for people and they don't like it. They want to set up barriers and say, "Well, only go this far; don't go the whole way." But, the idea goes the whole way. And it's got to go the whole way. And that's a very unsettling thought for many people.

NOVA: Does natural selection explain how humans evolved?

Dennett: Well, does natural selection apply to human beings, too? Of course, Darwin has to say yes. And this is very unsettling, because tradition has it that we are made in God's image, that we are ourselves creators, artificers, we're modeled on God, the creator, the artificer.

And if Darwin is right, then we become just another effect. No longer a cause, no longer an author, but just another place where natural selection has its way in the natural world. I think many people are terribly afraid of being demoted by the Darwinian scheme from the role of authors and creators in their own right into being just places where things happen in the universe. And that's deeply unsettling.

NOVA: Can people still be moral in a Darwinian world?

Dennett: For more than a century, people have often thought that the conclusion to draw from Darwin's vision is that Homo sapiens, our species—and we're just animals too, we're just mammals—that there is nothing morally special about us. I myself don't think this follows at all from Darwin's vision, but it is certainly the received view in many quarters.

In fact, I think that what one can see from a Darwinian account is how the addition of culture in our species turns us into a very special sort of animal, an animal that can be a moral agent in a way that no other animal can be.

NOVA: What is God's role in a Darwinian world?

Dennett: After Darwin, God's role changes from being the designer of all creatures great and small to being the designer of the laws of nature, from which natural selection can unfold, to being perhaps just the chooser of the laws. By the time God's role has been so diminished, he becomes a bit like a constitutional monarch, presiding ceremonially but not having any more work to do. Now, that's a place for God if it makes people comfortable to keep God as the presider over the universe. I suppose that is satisfying for many.

I don't myself need that role for God. My view is that creation itself, the universe itself, is the most wonderful thing deserving awe and respect. And that satisfies me as my substitute for God. Now, that's a view with an ancient tradition. Spinoza had a famous phrase, "God or nature, one and the same thing." I agree with Spinoza.

Sylvia Earle
Oceanographer

NOVA: Why does evolution matter?

Sylvia Earle: Why does evolution matter? There is so much about the evolution of life, the development of life on Earth that should rivet the attention of everyone to understand where we've come from and where we might be going. We need to understand the world around us if we are to succeed as a species on the planet. The observations that have developed over the years have given us perspective about where we fit in.

We are newcomers, really recent arrivals on a planet that is four and a half billion years old. The development of photosynthesis as a process is thought to be maybe in the vicinity of three billion years ago, maybe less than that. But whenever it happened, before that time, air-breathing, oxygen-dependent creatures such as we couldn't have survived, even with lots of water and rocks and the basic ingredients for life. It has taken these many hundreds of millions of years to fine-tune the Earth to a point where it is suitable for the likes of us.

NOVA: How does evolution change your view of a shrimp cocktail?

Earle: Most of life on Earth has a deep past, much deeper than ours. And we have benefited from the distillation of all preceding history, call it evolutionary history if you will. I suppose when some people look at a shrimp they think, "Hmm. Delicious." When I look at a shrimp I think, "You're a miracle, absolutely incredible. Your ancestors have gone back hundreds of millions of years. And to develop a thing as simple as a shrimp cocktail, you have to calculate the hundreds of millions of years that have preceded that moment where you're sitting there with your sauce and fork poised.

It's an appreciation for life generally, every bit of life, the smallest creature that lives in the intestines of termites that make termite life possible—to the leaves that turn out oxygen and grab carbon dioxide and with water make simple sugars that feed much of the world. I mean, these are everyday miracles.

NOVA: Is evolution something to be feared?

Earle: Evolution is not something to be feared. It's to be celebrated, embraced, and understood. We want to think of ourselves as truly special creatures that are unique in the universe and, well, we are. And we have that capacity to wonder, to question, and to see ourselves in the context of all of life that has preceded the present time, and all that will go off far into the future, one way or another. Rather than be afraid of it and try to stifle inquiry, people should revel in the joys of knowing and find a serenity and a joy in being a part the rest of life on Earth. Not apart from it, but a part of it.

NOVA: How many species live on our planet?

Earle: The number of species that are known for the planet as a whole, that have so far been described—it's about one and a half million. Of that number, about a quarter of a million are marine. That includes all the fish, all the crabs, all the shrimp, all the seaweeds, all the little arrow worms, the peanut worms, the polychaete worms, the jellies, the whole range, the spectrum of life.

But when you consider that we've only seen, well, less than five percent of the ocean, we are probably underestimating or underaccounting for the life on Earth by a large factor. Some say 10 million in the sea alone. Others say on the order of 100 million unidentified species.

The diversity of life on Earth, generally, is astonishing. But despite those large numbers, it's also important to recognize that every species, one way or another, is vulnerable to extinction. And in our time on Earth, especially in the last few decades, our impact on the diversity of life has been profound.

NOVA: What single image captures the essence of evolution?

Earle: It's that image of Earth from space that transformed our view of ourselves. It is maybe the most important image that exists—because we can see ourselves in context in a way that otherwise would be really hard to explain. It should inspire us to wonder about it, to want to know everything we can about it and do everything we can to take care of it.

This is a living planet. Look around. Mars, Venus, Jupiter. Look beyond our solar system. Where else is there a place that works, that is just right for the likes of us? It has not happened just instantly. It is vulnerable to our actions. But it's the result of four and a half billion years of evolution, of change over time. And it changes every day, all the time. It would be in our interest to try to maintain a certain level of stability that has enabled us to prosper, to not wreck the very systems that give us life.

NOVA: What would Darwin think if he saw what you have seen?

Earle: If Darwin could see what we now see, what we now know about the ocean, about the atmosphere, about the nature of life, as we now understand it, about the importance of microbes—I think he would just beam with joy that many of the thoughts and the glimpses of the majesty of life on Earth that he had during his life, now magnified many times over.

If Darwin could get into a submarine and see what I've seen, thousand of feet beneath the ocean, I am just confident that he would be inspired to sit down and start writing all over again.

Stephen J. Gould
Paleontologist

NOVA: Why must all of your students read the Origin of Species?

Stephen J. Gould: I always tell my classes that I would never dare to check up on them. They have to read the Origin of Species simply because it's one of the half dozen greatest books in the history of western thought. And simply to ask questions about it, to test whether they did it, would be a terrible affront to their intellectuality. Of course, the question they invariably ask is, "What are the other five?" [laughs] I say, "I don't know, but that's not the point." The point is, the Origin of Species is so important, and Darwin's theory is so important, that at least metaphorically you've got to rank it with the very few of the finest and most portentous achievements in human discovery.

NOVA: How is Darwin's revolution more important than Copernicus's?

Gould: Sigmund Freud said that there were really two great revolutions. The first that we associate with Copernicus and Newton and Galileo that taught us that we weren't living on the central body of a limited universe. And that Darwin's was the second that taught us that we were not separately created in the image of a benevolent deity but were part of a history of genealogical connectivity of all living things.

Now, in an odd sense, we know how contentious the first revolution was. We know the story of Galileo. But, contrary to popular understanding, the church made its peace with Galileo. They may not have taken his books off the index or officially exonerated him until recently. But a few years after his death, it was not a hot issue anymore because people knew the Earth goes around the sun, and that's all there was to it. And it wasn't going to do much good to try and base a theology on getting nature backwards.

But, the way I like to put it, I don't think that revolution was as important as Darwin's, because it's about real estate; the Darwinian revolution is about essence, it's deeper. The Darwinian revolution is about who we are, it's what we're made of, it's what our life means insofar as science can answer that question.

NOVA: Why is evolution the most "discombobulating" of all scientific discoveries?

Gould: Science can't tell us what our life means ethically. It can't tell us what we are meant to do as moral creatures. But, insofar as science can understand what we're made of, and what we're related to, the Darwinian revolution completely revised our ideas about who we are and what we're related to and how long we've been here and why we're on this Earth, again, in the limited ways that science can apprehend or comprehend those questions.

So it, in many ways, was the singularly deepest and most discombobulating of all discoveries that science has ever made. And that it is so factually firm and so well documented merely makes it all the more salient, because it isn't just a conjecture; it's an entire reconstruction of our concept of ourselves and who we are that is as well documented as anything we've ever learned in science.

NOVA: How is the theory of natural selection both simple and elegant?

Gould: I don't think there's ever been a complicated scientific argument, or an argument with such great impact upon the world, that really is so simple and so elegant in its formulation. I mean, natural selection is no more than three facts in one syllogistic deduction. That's how Darwin presents it in the first three pages of the Introduction in the Origin, and that's how teachers have done it ever since.

First, that all organisms produce more offspring than can possibly survive. And that's pretty clear. And Darwin starts talking about codfish that lay two million eggs twice a year, that's pretty obvious. But he even makes a calculation for the slowest breeding creature, African elephants, that have one young every eighteen months. And even if they all survived, you'd have the world full of elephants or anything in a geological moment. So that's the first fact, that all organisms over-produce offspring, so they can all survive [as species].

Secondly, that all organisms vary, and it's just folk knowledge. You just have to look around a room of people, and everybody knows that it's true. Darwin didn't know the mechanism of heredity, but you don't have to. You just need to know the fact of it.

Thirdly, at least some of that variation is inherited. And that's also folk wisdom.

So, you put those three facts together—that all organisms produce more offspring that can survive, that there's variation among organisms, and that at least some of that variation is inherited—and the syllogistic inference is natural selection. That is, environments are changing. If there's all this variation and not all organisms can survive on average, not every single time, but statistically on average, the survivors will be those whose variation fortuitously adapts them better to changing local environments. And then because they pass on those fortuitous traits to their offspring, the population changes.

That's natural selection. That's all it is, is just those three factors—over-production, variation, and inheritance combined to produce adaptation to changing local environments. It's not a principle or progress; it's just a principle of local adaptation. You don't make better creatures in any cosmic sense; you make creatures that are better suited to the changing climates of their local habitats. That's it.

Ken Miller
Biologist

NOVA: Can a traditional Catholic accept evolution?

Ken Miller: My students often ask me, "You say you believe in God. Well, what kind of God? Is it a fashionable New Age God? A pyramid power kind of God? Do you think, like some scientists do, that God is the sum total of the laws of physics?" And I shake those off and say that my religious belief is entirely conventional. I'm a Roman Catholic, a very traditional kind of religious person. And my Roman Catholicism is entirely conventional. It surprises students very often that anyone could say that that kind of traditional, conventional religious belief could be compatible with evolution, but it is. And it is in a remarkable way.

Sometimes I like to tell students, in a sense, that I believe in Darwin's God. Now, I don't mean that my religious beliefs or those of other scientists are exactly the same as Charles Darwin's. What I do mean is that my view of God is that of a deity who could set in motion and guide all of the processes that Darwin himself described.

So not only was Darwin right about the origin of species, and not only was Darwin right about the mechanisms of evolutionary change, but there's nothing about those origins or that mechanism of change that is inherently antithetical to religion, nothing in it that goes against religious belief. And, therefore, I sort of find this absolutely wonderful consistency with what I understand about the universe from science and what I understand about the universe from faith.

NOVA: What was Darwin's greatest obstacle?

Miller: In Darwin's day, the special qualities of the human being, the special properties of the human mind, could only be explained one way, and that was by the direct intervention of a divine creator—the creator of the human species—literally instantaneously out of nothing. In many ways, the most threatening aspect of all of Darwin's work was to suggest that the remarkable properties that make a human being special could be produced by the same brute force process of random variation and natural selection that had produced everything else in the natural world.

In a way, this was the most radical departure that was pushed forth by Darwinian thought. And for Darwin, it was a tremendous struggle, first of all within his own mind, secondly within the bounds of his own family, and thirdly within Victorian society itself—to get all of these groups to accept the idea that humanity could be produced by nature in the same way as every other species, and also that the special properties of the human mind could have been produced in exactly the same way.

NOVA: How does evolution "make sense" of biology?

Miller: Nothing in biology makes sense except in light of evolution. Without evolution, biology is just a bunch of disconnected facts. It's kind of structural postage-stamp collecting. We've got this, they've got that, this organ does this, this organ does that. And what evolutionary theory does is to provide a framework in which we can understand everything in biology. The sequences of our genes, the structures of our bodies, and even our instincts in terms of behavior—all make sense and all tie together because of evolution. We can understand everything by putting it into a coherent whole.

And that's why evolution is the key idea of biology. To anticipate a biological science without evolution would be like having chemistry without atoms. It would be like having physics without the laws of motion. It would be like astronomy without stars.

NOVA: Why is it critical to teach evolution in our schools?

Miller: I think there's at least three reasons why it's important to teach evolution in the schools. The first one is that the story of nature is incomplete without it. If we don't understand how we got here and what the forces were that shaped the modern world, then nature is just as it is now and doesn't have a sense of perspective as to what the past was like and how life has changed. So we have to teach evolution in order to complete that story and give students a sense of the history and the nature of the planet.

Now, there's a second reason. The second reason has to do with the fact that biology is really nothing more than an isolated collection of facts about various types of organisms without evolution to tie them all together. Evolution makes sense of things. The structures of our own bodies make absolutely no sense unless we understand their evolutionary ancestry. And that's another reason why evolution is important, because it organizes biology.

The third and, I think, in many respects the most important reason, is because evolution is a continuing process. New species continue to arise today, and that's an important thing to understand. And in many of the struggles and the battles that we face as human beings on this planet, we have to understand and we have to deal with evolution. And that's true whether you are a physician trying to administer antibiotics to control an infection, whether you're a farmer trying to grow crops and use pesticides and you're worried about insects evolving resistance to those pesticides, or whether you're trying to do something aseptically like develop a new drug or develop an organism that has a new capacity that will be useful to humankind.

Natural selection is the method, the force, that drives each and every one of those. So without an understanding of evolution, the story of nature is not complete, the inventory of biology does not make sense, and the appreciation of what goes on in the world around us is lacking as well. Evolution is important to tie all of those things together.

NOVA: What do you tell students who don't "believe" in evolution?

Miller: One comes across students who are predisposed to reject the idea of evolution, to have resistance to learning anything about Darwin and his theories. And I think given the nature of religious training, that's only understandable. What I try to tell my own students at the university level, and my teaching assistants, and the advice that I would give to schoolteachers is very simple: The purpose of scientific education is to educate. It's not to compel belief, it's not to indoctrinate. It's to promote understanding. And the goal is never to get students to accept or believe in the scientific idea. Lots of students find the idea of atoms and molecules remarkable. I recall in high school at one point I said I didn't believe in the Krebs cycle. It was too complicated. I wanted something simpler.

And what I'd like to tell my own students is that I don't really care if you believe or if you accept evolution or not. But what you should know is that evolution is the driving idea in biology that is accepted by the scientific community. And therefore, to become an educated person, you have to understand evolution.

James Moore
Darwin Historian

NOVA: Why did Darwin keep his ideas a secret for decades?

James Moore: Darwin was a young man on the make. And in his early career, science was creationist. To do good biology was to be creationist. That meant, generally speaking, that one believed that the first species of animals and plants were created by God miraculously. Now, there were some naturalists who believed they appeared "one knows not how," and there were some who believed that some law might regulate the introduction of new species. But everyone thought it was a mystery of mysteries. And, generally speaking, beyond our ken. One shouldn't look into it. It was a pandora's box of problems. Darwin decided to tackle this mystery of mysteries head on, and in so doing, he ran slap-counter into established science. He was doing something highly unorthodox in his day. Not unorthodox because it went against the church, per se, but because it went against all of natural history in Great Britain. It jeopardized the standing of science, it jeopardized the standing of a stable society, the Bible, and the church as well. So Darwin kept his thoughts to himself for many years and agonized over the problem until it was safe to go public.

NOVA: Why was evolution so feared in England in the 19th century?

Moore: Darwin's idea was dangerous, or he feared it was dangerous, in his own country, in his own place and time, mainly in the early 19th century. In France, evolution wasn't dangerous, in Germany it wasn't particularly dangerous. But in Britain, a country that had escaped revolution, and escaped it throughout the 19th century, the idea that humans could be related to ape-like ancestors and the rest of creation was considered subversive. If man was just an animal, then he doesn't live forever, he has no soul. And if men don't have a soul, then there's no afterlife. No heaven, no fiery deterrent of hell to keep people in line in this life. And if there's no fiery deterrent to keep people in line, "well then we might as well have hell on Earth!" the critics said. "We can just live however we like, because we're nothing but animals. And what happens? Revolution. Insurrection. Sexual immorality." Anyone who believed in evolution—or as they said in his day, transmutation—anyone like Darwin was a seditious person.

NOVA: Why did Darwin call himself "the Devil's Chaplain"?

Moore: There were plenty of people in Darwin's day challenging the establishment. Radical unbelievers, people who went from door to door and city to city to convert the people from Christianity to unbelief. One of them was called "The Devil's Chaplain." He trained for the church at Cambridge, he was in holy orders. Then he became an unbeliever and he stumped the country, trying to convert to his brand of irreligion. The Devil's Chaplain was a term that Darwin applied to himself when he was writing the Origin of Species. Now, the word "Devil's Chaplain" is oxymoronic, isn't it? It's a contradiction of terms, of the devil and yet a chaplain. There's a dilemma in that term, and it was a dilemma Darwin felt acutely. On the one hand, he was respectable, he had trained for the church in Cambridge, a Chaplain. On the other hand, he was saying things that people regarded as diabolical, the devil. And so he was torn by this dilemma, and that's why he applied the term to himself, I believe. On the one hand, a respectable man, on the other hand, a respectable man with a dangerous theory.

NOVA: Was the Origin of Species a "bombshell" in Victorian England?

Moore: The publication of the Origin of Species is often treated as it were a bombshell that exploded on the playground of science and created a tremendous destruction, and, you know, wrecked society, and all kinds of miserable things. It's not so. Darwin was a well-known naturalist, he had a high reputation because of his work on barnacles, for example, and it was well known in scientific circles that he was working on a big book about species. People weren't quite sure what his leading idea was, but it was expected. The only thing that was unexpected for Darwin was that it was forced from him when he received a letter from a young naturalist named Wallace, with what looked like a version of this theory in the letter. So Darwin was surprised, he got busy and wrote the Origin of Species, in a kind of condensation of the big book he'd been working on, and when it came, of course, people snapped it up. Everybody reviewed it, it was taken very, very, seriously. There were a few moans and a few howls, but insignificant. Even those people who were most opposed to Darwin had to take it seriously, he had such an enormous reputation.

The old guard, the old Anglicans, the old naturalists, people born in the early years of the century—in the 18th century—now in their 60s and 70s, they despised it. They despised its tendency, but they respected the author.

Radicals—old radicals, new radicals, people who were into social revolution and change and knocking the church—loved it. Even though Darwin often referred to the creator in the Origin of Species, they still loved the book. It was a perfect weapon to throw at the establishment.

Where the Origin really got accepted was amongst younger naturalists, younger men of science, who realized that its theory of natural selection gave them a new way of looking at nature. All kinds of questions arose. It was a fruitful research program to embark on, to test Darwin's theory. And that's really the story of the rest of the 19th century. A kind of "mopping up operation," as one new naturalist after another converted, not always to natural selection, but to the theory of descent with modification, evolution as Darwin conceived it. And that was his most important achievement of the 19th century.

NOVA: Would Darwin have been surprised by today's culture war over evolution?

Moore: Well, Darwin was his own man, and he belonged to his own time, so it's very difficult to say what he would think if he lived now. But we do know what he thought about the future when he was living, and, therefore, perhaps what would surprise him if he had lived into that future, Darwin would have been surprised and appalled by two phenomena.

One is the truculence, the sheer pugnacity of his champions today. The ease with which they are prepared to draw atheistic conclusions from his theories, conclusions he himself would never have drawn. And, on the other hand, Darwin would have been surprised and appalled at the resurgence of beliefs, Creationist beliefs that he believed like so many 19th-century thinkers would gradually wither away.

Darwin believed in intellectual progress, but he believed that it would come smoothly and harmoniously and happily and it would eventually cover the whole world. If he were here today, he would be gravely upset, I believe.

Image Credits

Clockwise From Top:

(Stephen Jay Gould)

© WGBH Educational Foundation

(Sylvia Earle)

Courtesy DOER Marine

(Dan Dennett, Ken Miller, James Moore)

© WGBH Educational Foundation