ALLEN MACNEILL: During the first half of the 20th century, the founders of the modern synthesis rehabilitated Darwin's theory of evolution by natural selection, integrating it with Mendelian genetics, population genetics, developmental biology, ecology, paleontology, and many other branches of the biological sciences. This reintegration was substantially complete by the centennial of The Origin of Species in 1959.
This photo, taken at a celebration of this centennial held at the University of Chicago, shows three of the founders of the modern synthesis-- G Ledyard Stebbins, a botanist; George Gaylord Simpson, a paleontologist; and the man many people credit with kicking off the synthesis, Theodosius Dobzhansky, a fruit fly geneticist.
I'm here speaking in front of this reconstruction of a placoderm with Will Provine, the Tisch Distinguished Professor at Cornell University. In 1998, Will co-edited a volume on the modern synthesis with Ernst Mayr. The modern synthesis, as we've said already, is a collaborative effort among many different evolutionary biologists that took place during the first half of the 20th century.
Will, people who have learned about evolutionary theory have heard about the modern synthesis. Can you tell me what it was?
WILL PROVINE: Sure. But it's best done by explaining that is also known as 20th century Darwinism. And so it's best to talk about it in terms of what Darwin himself did and what 20th century Darwinism a century later was really like.
Darwin had a true synthesis of all the parts of evolutionary biology. That is, he starts off and talks about evolution by descent from common ancestors. And then he explains natural selection. But he brings in everything else, from embryology to morphology-- which is the study of forms-- to-- all parts of evolutionary biology were part of his view.
Well after that-- and then he really got going on evolutionary biology. And all the pieces of it got developed separately. And it wasn't until the 1930s and 40s that people began to pull all these parts of evolutionary biology back together again. And this is known as the evolutionary synthesis or 20th century Darwinism.
And the reason why it's called 20th century Darwinism is that it looks very much like Darwin's view, except that natural selection has taken a greater importance. The people who developed this view were primarily Theodosius Dobzhansky and Ernst Mayr, as general biologists. But there was also a component of it known as population genetics, that is a core of quantitative evolutionary biology.
This was developed by RA Fisher, Sewall Wright and JBS Haldane. This triumvirate worked out many aspects of evolutionary biology on a quantitative but simplified basis. And this quantitative background became terribly important in 20th century Darwinism.
ALLEN MACNEILL: F Will, it's not exactly that the modern synthesis or the evolutionary synthesis is dead. It's just that it's been superseded. Where do you think evolutionary biology is going to go in the future? And how do you think people should approach it?
WILL PROVINE: One thing is terribly exciting to me right now. I learned evolutionary biology in the late '60s. And this was the evolutionary synthesis. That's what I learned.
And now I would say evolutionary biology is about 10 times as interesting as it was when I learned it. It was kind of dead knowledge by the time I got it. But now it's really becoming alive.
We've discovered that Darwin's idea of evolution by descent from common ancestors does not really work well, as soon as you get behind multicellular organisms, though there's 3 billion years of evolution in which there isn't enough lateral transfer. And our methods of phylogeny reconstruction are so poor that we will never have a tree of life that goes back to the origin of life.
To me, that's incredibly exciting. And there are many other things about molecular evolution, its connection with embryology. So now we can have an evo-devo evolutionary biology that's really true and real.
It's also very exciting to see how quantitative evolutionary biology has progressed. We've never been able to study evolution from a genealogical point of view, that is, treating humans as if they have only two parents rather than just one. We can study evolution in mitochondrial DNA. You can just go back in time to do that. But that's all through females.
We can do it with Y chromosome. And to get a most common recent ancestor for us, oh boy, that was terrible. It took 200,000 years. And now that we can do this in a genealogical way, it turns out our most recent common ancestor is only about 10,000 years old.
I think evolutionary biology is at the cusp of being its most interesting at any time since Darwin. And so yes, I'm very excited about the future of evolutionary biology.
ALLEN MACNEILL: In The Origin of Species, Charles Darwin presented two different but related theories of evolution-- his theory of descent with modification and his theory of evolution by natural selection. Descent with modification is the history of life on Earth. And the theory of natural selection is about the process by which this history has taken place.
In the 20th century, these two ideas have been translated into the theory of microevolution and the theory of macroevolution. Microevolution is those processes that make evolution happen. Macroevolution by contrast is the process that microevolution drives. If you want to think of it this way, microevolution is like the engine of the car. And macroevolution is like the road map that the car has followed.
A good place to read such a road map is at a museum like this one, the Museum of the Earth at the Paleontological Research Institution in Ithaca, New York. This is Dr. Warren Allman, the director of the Paleontological Research Institution and a professor of paleontology at Cornell University. Warren, throughout this series, we've been talking about how scientists have developed the theory of evolution by natural selection. What part does an institution like the Paleontological Research Institution play in the development of that theory?
WARREN ALLMAN: Allen, paleontology is an integral part of any theory of evolution. And Darwin recognized that. And a place like this, a natural history museum, specializes in collecting objects that document that history.
So PRI's collections of about 3 million specimens, which is one of the largest in the country, documents really hundreds of millions, even billions of years of the history of life. That's relevant, as you said, to two things-- to documenting the history of life-- macroevolution, where evolution has gone, where it has come from.
It's also increasingly relevant to discussions of mechanism. One of the things that's happened in the last 30 or 40 years in evolutionary biology is that discussions have gone on that perhaps microevolutionary mechanisms of the sort that we can see on human or ecological time scales-- decades up to centuries-- might not be all there is. There might be other mechanisms that are macroevolutionary mechanisms. And clearly, those are completely invisible on a modern time slice but might be visible as we look at the fullness of geological time, as represented by the fossil collections in a place like this.
ALLEN MACNEILL: Warren, we've been talking about macroevolution. In the 20th century, the person who's name is probably most associated with macroevolution was Stephen Jay Gould. Could you tell me something about his theories and your relationship with him?
WARREN ALLMAN: Steve Gould was my graduate advisor at Harvard. And so he was very influential to me personally, of course. But as you say, he was probably-- whether you agreed with him or not, he was probably the most influential person connected to macroevolution in the late 20th century.
And it's important to note that. Because you don't have to agree with everything that Steve Gould said or thought or wrote to understand that his influence was probably mainly in raising questions that hadn't been raised before or raising them in different ways. He was primarily a paleontologist. And so he thought in long time spans, what we've all now come to use in John McPhee's term, deep time.
And deep time gave him the perspective of looking at trends and saying, are those long term trends in the fossil record over millions of years? Could they have been produced only by the mechanisms of natural selection acting on very short time frames? Darwin, of course, reduced macroevolution to microevolution, that was the genius of Darwin's argument.
And Gould and people that thought like him said of course Darwin was correct. But was Darwin adequate? Did Darwin say all that there was to say?
And so principally, but not only, through punctuated equilibrium Gould suggested that there could be processes in the history of life, macroevolutionary processes, that literally could not be produced by microevolutionary processes that, say, somebody could study in the laboratory today.
So what are those processes? They weren't mystical. They were not sudden evolutionary leaps, as it was often caricatured in the popular media.
It was simply that if natural selection can't push organisms in an optimal direction-- what if natural selection isn't powerful enough all the time to make organisms as good as they could possibly be-- then perhaps long term trends that make horns bigger or make fish bluer or make shells bumpier, maybe those long term trends aren't due to only natural selection acting on very small frames. Maybe they are also-- or more so-- due to the pattern of sorting among species that remain relatively stable during their lifetimes.
ALLEN MACNEILL: And so we've come to the end of our brief exploration of evolutionary biology. As we have seen, Darwin's theory was both revolutionary and at the same time a natural outgrowth of a way of looking at reality that began over 2,000 years ago. Scientists don't claim to know all the answers. Nor do they believe that all of the answers are possible to find.
What they do have is a deep sense of curiosity about the natural world, a curiosity that drives them to find out the way that things work, to answer the questions, what is this, how does it work, and why does it exist. Perhaps Darwin himself said it best at the conclusion of The Origin of Species.
"It is interesting to contemplate an entangled bank clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about and with worms crawling through the damper, and to reflect that these elaborately constructed forms, so different from each other and dependent on each other in so complex a manner have all been produced by laws acting around us. There is grandeur in this view of life, with its several powers having been originally breathed into a few forms or into one. And that whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning, endless forms most beautiful and most wonderful have been and are being evolved."
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Published 150 years ago, Charles Darwin's
On the Origin of Species provided the foundation for the modern science of biology. It also set in motion a revolution in the sciences and in our understanding of ourselves and our place in nature.
This CyberTower Study Room is a brief introduction to Darwin's theory and its implications. Beginning with an overview of Darwin's predecessors, we learn how Jean Baptiste Lamarck set the stage for Darwin's monumental achievement with his Philosophie Zoologique, which advanced a theory of evolution by means of the inheritance of acquired characteristics.
Darwin, whose academic training at Cambridge University was in Anglican theology, became an acclaimed naturalist and science writer following the five-year voyage of HMS Beagle. Using the notes and specimens that he had collected during the voyage, Darwin spent twenty years refining his theory, first published in 1859, of evolution by natural selection.
In the last segment of this Study Room, we visit the Museum of the Earth in Ithaca, New York, whose director, Dr. Warren Allman, discusses the importance of such museums to the science of evolutionary biology. We also hear from Cornell professor William Provine, who discusses Darwin's work and its importance to the history and philosophy of biology.
This video is part 6 of 6 in the Darwinian Revolutions series.