Part 1: The Idea of Evolution - A History
The time is 1925. The place is Dayton, Tennessee. In this Rhea County Courthouse the two most famous lawyers in America argued for and against a seventy-year-old scientific theory called evolution by natural selection.
On trial was a young high school science teacher named John Scopes. Scopes, it was charged, taught his students that living things had evolved over millions of years from more primitive ancestors. Scopes believed and taught that man was descended from the monkeys, charged the prosecution's lawyer, the famous William Jennings Bryan.
Such a view, claimed Bryan, was absurd, was contrary to Holy Scriptures and was against the law in Tennessee. (In the popular press the trial was called "the monkey trial."
His opponent, the famous defense lawyer Clarence Darrow, argued that the Darwinian theory of evolution by natural selection was the most reasonable explanation for the variety and similarity of life on earth. Furthermore, said Darrow, the Tennessee law was unconstitutional since it prohibited free speech and put religion into the state's public schools.
The Scopes trial soon became an international sensation. Reporters from around the world crowded into the small town in Tennessee to record the drama for their readers. People in Dayton, and around the world, took sides in the controversy. A poll of the day found the courtroom equally divided, for and against evolution.
The trial's outcome was something of an anticlimax. Scopes was found guilty of breaking the Tennessee law against the teaching of evolution and was fined $100. The conviction was later overturned on a legal technicality. The sensational publicity of the trial, however, served to make a hero out of Scopes and hold Bryan and the cause he represented up to a good deal of ridicule. Bryan himself, broken in health and spirit, died in his sleep only a few days after the trial's verdict in a front parlor in Dayton.
The Scopes trial was the most famous. There have been many other conflicts the past 150 years over the scientific theory called evolution by natural selection. Some of these conflicts have been scientific ones, but many have been political and religious as well. Let's look at the world history of this idea, one of the handful of scientific concepts that are keys to scientific literacy today.
People from ancient times could not help noticing there was a great variety of plants and animals in the world. For the most part most people were too busy trying to survive in competition or cooperation with these other living creatures to give much thought to why there were so many. And to how they got to be the way they were. In some ways so like humans and in so many other ways so very different.
To those who did have the time or inclination to speculate about such questions, the most common answer was that a god or gods made them that way. Many also believed that the same god or gods made other living creatures to please and serve mankind.
In the ancient Ionian cities of Greece (now in ruins on the western coast of modern Turkey) some of the world's first scientist/philosophers dared to ask and answer questions like this in a different way.
Anaximander in 550 BC proposed a theory of evolution to explain the variety and likenesses among living things. All life, he said, has come from early life in the water. Over long periods of time, the water creatures crept out on the land, developed legs, then fur and finally human forms. Anaximander did not have much evidence to support his theory, nor did he have any ideas just how this kind of near miracle could have actually taken place.
One of the handicaps early thinkers had was massive ignorance about living things. They knew of the existence of only a tiny fraction of the variety of plants and animals that live on this earth. Aristotle, one of the first to invent a scientific classification, found room for about 500 species of animals. As late as 1600 only 6000 species of plants were known. By way of comparison, today over 2 million species of living things have been described.
In the high days of Renaissance science, when giants like Copenericus, Galileo and Isaac Newton were shaking the foundations of human knowledge about the earth and its place in the solar system, biology was in its infancy.
True, men like Vesalius and William Harvey were disproving some ancient misconceptions about the way the human body was built. The Dutch lens maker, Leeuwenhoek, was the first to view the wonder world of microscopic "little beasties." Still, little progress was made in developing any unifying ideas or in accurately describing and classifying knowledge about the complex living world.
In the eighteenth century, about the same time the American colonies were beginning to change into the United States, humankind's store of knowledge about this complex living world began to rapidly increase. Explorations into the far corners of the world were becoming more and more common. Many of the explorers were returning with specimens of new species of plants and of animals never before known to western scientists. And more and more men were becoming scientists. In those days there were few if any professional scientists- that is, people who made a living searching for answers to questions about nature. So it was that "amateur" scientists like our own Benjamin Franklin and Thomas Jefferson were among the first of the human race to devote their skills to the scientific study of living creatures.
One of the most important of the early pioneers was Carl Linnaeus of Sweden. Linnaeus, unlike most early scientists, was a poor boy. He hated school but he loved plants. As a young university student, poor and hungry and plagued with gout, he left on a field trip to Lapland to collect plant and animal specimens. The 4,600 mile trip cost him only $100. The knowledge he gained on this trip paid off handsomely for all of us.
A few years after his trip in 1735 Linnaeus brought out his first book, Systema Naturae. It was a great scholarly hit and he became an instant celebrity. In this book he proposed a classification system for plants and animals that is still being used today.
All living things, suggested Linnaeus, should be grouped according to a natural and logical system he proposed. Each kind of living thing would be given a unique double name in internationally accepted Latin. First would be its genus. Followed by its species. It was called a binomial nomenclature system.
Similar genera would be grouped together into families; families into orders; orders into classes; classes would be grouped into a few major phyla; and finally, phyla into kingdoms. It was a system that for the first time brought order and system into the study of the living world. Linnaeus helped people see the reality of living species but he himself opposed the idea that living species had ever evolved from common ancestors. He saw his work of inventing and promoting the present classification system as the scholar's humble way of "tracing the footprints of the Creator."
One of the most important was a Frenchman, Georges Buffon. A charming, elegant man of great wealth, Buffon was able to devote his life to scientific study without worry of earning a living. He founded one of the first genuine biological research centers of the world, the Jardin de Roi (Garden of the King) in Paris. He is said to have started his work day at 6 a.m. each morning, taking two breaks each day to have his hair dressed and powdered. In between many love affairs and a few duels, he managed to write forty-four volumes of natural history. These volumes summarized all that was then known about the natural world. In some of these volumes he anticipated many of the ideas of Darwin and later evolutionists, but he never quite put together a convincing theory to explain the mechanisms of evolution.
The books were convincing enough to the religious authorities, however. They brought him before the Syndic of the Sorbonne in 1751 where he was commanded to withdraw portions of his books that seemed to contradict Holy Scriptures. One of the parts the religious authorities most objected to was Buffon's estimate of the age of the earth as on the order of 100,000 years. Biblical doctrine held that the earth was created in 4004 B.C.
Another Frenchman, Jean Baptiste Lamarck, built on the foundations laid by Buffon to construct one of the first fully formed, genuinely scientific theories of evolution. As poor as Buffon was rich, Lamarck took over the Jardin de Roi when it became the Jardin des Plantes after the French Revolution. (Which revolution was also executed Buffon's aristocratic family.) Teaching himself zoology after the age of fifty, Lamarck proposed a theory of evolution with he said reflected the natural order of animals in nature. It's key ideas were two: nature has an innate tendency to evolve in the direction of increasing complexity, and acquired characteristics will be passed on to offspring. In this way nature will slowly move toward increasing variety and complexity to fill up all the niches in the living world.
Lamarck also has the distinction of being the first to coin and use the world "biology."
Paradoxically, one of the Lamarck's most critical scientific opponents, the anti-evolutionist Georges Cuvier, laid even more important groundwork than did Lamarck for the later flowering of the Darwinian evolution theory.
Cuvier worked at the same Museum of Natural History in Paris in the late eighteenth and early nineteenth century. He is credited with founding the science of paleontology- the study of plant and animal fossils.
Before Cuvier, fossils were known but little understood. The most common view was that fossils were freaks of nature placed there to amuse and mystify humans. Cuvier spent many years systematically studying fossils found in the limestone deposits around Paris, as well as those brought to the Museum from all over the world. He compared the forms left in the rocks with the anatomical structures of living creatures of his day. He became the world expert in reconstructing an entire animal from a few fossil bones. And he concluded from his study that fossils were prints of former creatures, prints that had been made in great catastrophes of the past, the greatest of which was the flood described in the Bible when Noah built his ark.
The opposite geological view was taken by the Scotsman generally given credit as being the father of modern geology, James Hutton. Hutton viewed the earth as having no "vestige of a beginning, no prospect of an end." He saw earth as changing in the past, changing today and changing in the future. These changes occurred very slowly but surely over very long periods of time from the same geological processes you could see happening today: mountain building, erosion, volcanoes and earthquakes.
Hutton's ideas were advanced and popularized by Charles Lyell, whose book Principles of Geology became the first classic work in geology and an important influence on biology as well. By the mid-nineteenth century ideas about the possible evolution of living forms were widespread, but no one had yet convincingly demonstrated how it could have happened. The man deserving the most credit for doing so was an English gentleman, Charles Darwin.
Darwin as a young man was not considered promising. His father once told him "you care for nothing but shooting, dogs and rat-catching, and you will be a disgrace to yourself and your family." When he got the chance to go on a round-the-world voyage as a young unpaid naturalist he snapped up the opportunity. The rest is history. Darwin's five-year voyage of discovery on HMS Beagle changed the world.
Here is the way he cautiously, but accurately, summarized the voyage in the first sentence of one of the most famous works of science of all time, "On The Origin of Species by Means of Natural Selection."
"When on board HMS Beagle, I was struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to throw some light on the origin of species-that mystery of mysteries."
When Darwin got back to England his health was broken. He married, though, and had a large family. Fortunately he inherited wealth from his family and did not need to earn a living. Instead he settled in a country home in Down, just south of London to a life of quiet study.
On his daily walks behind the house overlooking the quiet English countryside Darwin gradually pieced together his theory of evolution by natural selection, the theory of evolution that in broad outline is still accepted today as one of the bedrocks of modern biology.
As so often happens in science, at almost the same time another man was coming to much the same theory. That man was Alfred Russell Wallace. In outline Darwin and Wallace's theories were almost identical and surprisingly simple. In nature, they said, living creatures have more offspring than can possibly survive. The result is a struggle for existence. Since offspring vary, some will be more fit than others to survive. These survivors will pass on their useful traits to their offspring. Thus, in time, nature will select the most fit to survive. And, much as a gardener artificially selects traits he wants to survive in his plants, or as a cattle breeder selects traits he wants in his cattle, nature's selections will create whole new kinds of living things. New species.
Darwin's book On the Origin of Species by Means of Natural Selection and his following book The Descent of Man piled one piece of evidence on another to illustrate and support his theory. Not everyone was convinced of course. In his day Darwin was ridiculed unmercifully from the pulpit and in the popular press. Also from some 19th century scientists. In our day, however, in the 21st century, the accumulated evidence supporting the theory of natural selection of Charles Darwin and Alfred Russel Wallace is so overwhelming it has convinced almost all scientists around the world. As one prominent 20th century biologist put it, “Nothing in biology makes sense except in the light of evolution.”
There is still controversy however. Although almost all scientists as well as many people of all faiths now accept the Darwinian theory of natural selection some will add that behind the scenes of organic evolution, it is God who is responsible for the living ascent, and most especially for the human soul. Many people in the United States-- though not so many in most European and many South American countries – still hold to a literal interpretation of the Bible and insist that all species were created at one time, with many species being destroyed in one great catastrophe, the Biblical flood. Some of these fundamentalist Christians have recently organized to search for scientific support for their Creationist views. Recently some have proposed an alternative to Natural Selection that they call Intelligent Design. Some have initiated court suits and legislative bills to force the public schools to give equal time to Creationist and/or Intelligent Design points of view.
Within the scientific community today there is no disagreement about the fact of evolution. There is inquiry and disagreement over some of the details of natural selection theory. Like all scientific theories, Darwin’s is open to change in the light of new evidence.
We’ll examine these facts and that evidence in Part 2 of this program.
Part 2: Evolution by Natural Selection
"Glory be to God for dappled things for skies of couple-color as a brindled cow; for rose-moles all in stipple upon trout that swim; fresh-firecoal chestnut falls, finches wings ... Whatever is fickle, freckled (who knows how?) with swift, slow; sweet, sour; adazzle, dim; He fathers forth whose beauty is past change; Praise Him!"
That's how the poet, Jesuit priest and classical scholar, Gerard Manley Hopkins, celebrated the living world in 1877. The same living world that his neighbor, Charles Darwin, English gentleman, father and scientist, had just explained (and celebrated) in two books that have become classics of science, "On the Origin of Species by Natural Selection," and "Descent of Man."
To understand the differences (and the likenesses) between these two approaches to truth, let's first look at Darwin's contribution. His theory of evolution by natural selection is one of a small number of key scientific concepts needed to make sense of our modern world.
There are over two million different species of plants and animals on earth today. Why are there so many? And why, despite this incredible variety, are all living things so much alike in their basic chemistry? Alike in their living structures and alike in their ways of surviving and reproducing?
And finally, how are today's living things related to those other living things whose fossil remains are found so abundantly all over the world?
The theory of evolution by natural selection answers all of these questions this way:
1. Living creatures have more offspring than can survive. 2. There is variation in these offspring.
3. Some variations give an advantage and some make for a disadvantage in an inevitable struggle for survival.
4. The more fit will survive and pass on their desirable traits to their offspring.
5. In this way living things will change. Given enough time, whole new species of living things will evolve upon this fruitful earth.
It sounds simple. And it is. That is part of the beauty of any good scientific theory. It accounts for a wide range of individual events, using a bare minimum of general principles. Simple or not, what evidence is there to support this theory? Answer. A great great deal. And from many many different scientific disciplines.
First, and perhaps most important, there is the fossil record itself, nature's history book.
Fossils are the records in stone inadvertently left by living creatures of the past. Some are imprints of leaves, footprints, bones or droppings that have been covered over by sand or mud, and hardened into rocks that have survived for millions of years.
Sometimes we have actual fragments of plant and animal parts- pollen grains, teeth, bones, etc. Comparing these fragments to other similar structures in living organisms today, and with the knowledge that modern anatomy, physiology, geology, physics and biochemistry can provide, paleontologists have been able to construct a record of life in the past, as remarkable for its detail as for its drama.
Here are some highlights of that record-that world history- that are generally agreed upon by almost all experts who have carefully studied the fossil evidence.
The oldest fossils we have been able to find and identify come from rocks that were formed about seven hundred million years ago. In those days life was only found in the ocean. It apparently had been that way for over three billion years before that.
During that three billion years, however, life had branched, had changed, had evolved into many thousands, perhaps millions of different species. Each species had its own particular skill, its own particular advantage in the life struggle. Some species developed a chemical process to make use of direct sunlight as a source of life energy. Today we call that process photosynthesis. These organisms were the ancestors of all our modern plants.
Some species developed ways of moving, of capturing food, of digesting food, of sensing light, heat and sound. These organisms in the ocean were the ancestors of our modern animals, fish, frogs, grizzly bears and human beings. One of the clearest proofs we have that all of us, oak trees to frogs to human beings, have evolved from these common ancestors in the primeval ocean is the astonishing similarity in all of our life chemistries.
Whether you happen to be an oak tree or a frog or a human being, if we chemically analyze what you are made of, we find the same basic elements, compounds and mixtures. And always in very similar saltwater suspensions!
Most amazing of all, that saltwater suspension is very similar to the saltwater content of the ancient ocean! It can give you an eerie feeling: to taste your tears, or the sweat from your brow, or the blood from your cut finger, and suddenly realize that the salty taste comes from the "ocean" you still carry around inside you. The same ocean your single-celled ancestors lived in so long long ago!!!
Sometime around six hundred million years ago the seas began to teem with many-celled creatures. Cells had learned to clump together, and to specialize. And to make strange looking creatures like trilobites, snails and sea scorpions. Sometime around six hundred million years ago the seas began to teem with many-celled creatures. Cells had learned to clump together, and to specialize. And to make strange looking creatures like trilobites, snails and sea scorpions. Another hundred million years go by and the variety increases. We find fossils of creatures that are direct ancestors to modern octopus, squid and horseshoe crab. Wait another hundred million years and the first vertebrates- animals with backbones-appear.
About four hundred million years ago life first began to take the giant step onto land. Plants were the first pioneers, creeping out in inconspicuous ways like modern rock-hugging algae, mosses and liverworts. Animals followed. Insects, scorpions, and finally the first land vertebrates, lungfish and amphibians.
When we trace life history this way, it is not just imaginative speculation. We have millions on millions of fossil imprints of these creatures. And we have many ways of geologically dating the rocks these fossils are found in. Radioactive decay, geological strata and new sensitive chemical techniques are examples.
Many scientists would prefer to call this story of life changing on earth a fact, not a theory. That the changes occurred is as well-documented as anything can be in this uncertain world. The theory comes along to explain how the changes could have occurred the way they did.
Once life successfully made the step onto land and learned to use free oxygen in the atmosphere for respiration, life also began to develop thousands of new variations. The Age of Reptiles began with small scale-covered creatures and accelerated into mammoth dinosaurs. And split off into winged creatures that one day would lead to the whole gorgeous tribe of modern birds.
This was also the age of giant fernlike trees that, in dying and decaying under ancient swamps, would one day be covered by sand, compressed and altered by heat and pressure into what we today mine as coal, oil and gas. By two hundred million years ago the first birds do appear. And only sixty-five million years ago we first see the fossil remains of furry creatures with milk glands who gave birth to live young--the first mammals.
To get these enormous time scales into perspective, imagine you are making a time-lapse motion picture of the progress of life on this planet. Let each second of your movie show twenty-four years of life. On this scale 1,440 years will flash by in one minute; 86,400 years an hour; two million years a day. To show the story we are just telling, start some 730 million years ago in the ancient ocean. Your movie will then last one solid year, showing it nonstop twenty-four hours a day. Start the movie on New Years day.
The trilobites will first appear on the screen in early spring. By the end of May, fish will swim by. Not till midsummer will we see land animals and plants begin to test the free air.
In September, October and November the most spectacular actors in our movie appear-the dinosaurs. These improbable, incredible creatures dominate our screen for three months! This is called the Mesozoic era. It lasted over 260 million years. And then suddenly the dinosaurs all mysteriously disappear in early December.
The stars now become the mammals, with brains superior to anything that has come before. By the middle of December we will see monkeys, apes and other primates. But it will not be until the very last day of our year-long movie that anything resembling a human being appears.
The fossil finds of very early human beings are multiplying every year so the details of the final three million years of life history are being revised often. We know that there were quite a few human types. Neanderthal, Cro-Magnon, Pithecanthropus, Homo erectus and our own Homo sapiens.
Homo sapiens, "man the wise," did not appear until about forty thousand years ago, a mere half hour before the end of our movie. These people, our direct ancestors, slowly learned to cooperate in the hunt, in the gathering and preparation of food, in communicating in language, and finally in becoming fully conscious of their unique place in the living world. This final conscious stage may not have happened until very recently in earth history-some scholars say not more than five or six thousand years ago, during the time of the early civilizations, two or three minutes before the end of our movie!
And then in that final three minutes what a climax! The Egyptians, the Babylonians, the Chinese, the Indians, the African civilizations rise and fall. Some brave thinkers along the shores of the Mediterranean in Ionian Greece begin to ask the first scientific questions, and give scientific answers.
One minute to go. Jesus Christ is born. Twenty seconds to go. Columbus discovers America. Seven seconds to go. The Declaration of Independence is signed in Philadelphia. Three, two, one second- electricity, automobiles, power plants, jet planes, and space satellites zoom across the screen.
Leading to the most momentous event of our entire movie. Less than one second before the end of the movie you are born. The latest and thus far most promising experiment of life on this small planet we call earth.
That is what happened. How did it happen? How can you explain it?
1. Living creatures have more offspring than can survive.
2. These offspring have variations one from another.
3. The variations of one give it an advantage over another in a struggle for existence.
4. Those organisms with the most useful variations will survive and pass on their useful variations to their offspring,
5. Given enough time, and our movie shows how much time there has been, life will branch and branch and branch some more and some more and some more until we have what we have today.
And is that the whole story then? And do all agree? No. There is much disagreement today about evolution. And much new research actively proceeding.
The disagreements are of two sharply contrasting kinds however. Scientifically there is broad agreement about the overall picture but there is disagreement and uncertainty about some of the details of earth history and of the Darwinian theory of natural selection that explains how life changed over the ages.
The late Steven Jay Gould, for example, was a leading figure in investigating and presenting what he called a "punctuated equilibrium" theory. This is still Darwinian evolution by natural selection. Gould, however, claimed that the evidence was in favor of sharp changes in an evolutionary branch rather than slow continuous variations. These sharp changes would come when genetic mutations combined with changes in the environment. It was this combination that would lead to the birth of new species.
Mutations themselves-sudden changes in the molecular genes of a living organism are under much active study today. We can see evolution going on remarkably fast today in the cases of bacteria changing to become immune to our latest antibiotic. Or of insects changing their hereditary structures to escape the harmful effects of our latest insecticide. Or of some species moving to fast extinction because they could not cope with our latest environmental reconstruction.
There is also much disagreement over the role of natural selection when it comes to cultural evolution. What role, if any, has it had in racism, sexism, political and social changes? What role, if any, should it play?
Besides the churning of scientific disputes, there is today, as there was in Darwin's time, a bubbling of conflict between religious beliefs and evolutionary ideas.
Modern "scientific creationists" and “Intelligent Design” proponents dispute the entire evolutionary picture presented here. In its place they have their own interpretations which place heavy reliance on ideas of geological catastrophes in the recent past, especially the Biblical flood.
The overwhelming consensus of professional biologists, geologists, paleontologists and astronomers is that the Creationists and Intelligent Design proponents are simply mistaken about this. Scientists point out that their so-called “theories” do not qualify as scientific theories because they cannot tested nor do they lead to any new possibilities for productive research. Recent court cases have agreed and have ruled that "scientific creationism" (as well as its offshoot, Intelligent Design) is religion, not science.
On the other hand, there is little consensus among scientists or nonscientists about broader issues of meaning and value that may transcend science. Perhaps Charles Darwin himself should have the last word here. When he took that five-year trip around the world as a young unpaid naturalist on HMS Beagle, trip that eventually brought a revolution to biology and to society, here is one of the first things he wrote in his diary,
"Here I first saw the glory of tropical vegetation. Tamarinds, Bananas & Palms were flourishing at my feet ... I expected a good deal ... I was afraid of disappointments: how utterly vain such fear is ... I returned to the shore, treading on Volcanic rocks, hearing the notes of unknown birds. It has been a glorious day, like giving a blind man eyes. -- he is overwhelmed with what he sees and cannot justly comprehend it. -- Such are my feelings, and may they remain."
Indeed a deep understanding of evolution by natural selection is like “giving a blind man eyes.”