Charles Darwin Explains the Diversity of Life
Charles Darwin was an unlikely candidate for scientific stardom. As a young man he was not considered very 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." He entered college planning to be a clergyman, but when he got a chance to go on a round-the-world cruise as a young unpaid natualist, he snapped up the opportunity.
Darwin's five-year voyage on HMS Beagle led to a revolution in'the way we look at the natural world and to a new beginning for all of biology.
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 as a naturalist, 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."
These facts led Darwin to propose his theory of evolution by natural selection-the single niost important unifying theory in biology.
Darwin, of course, did not start from scratch. Before examining his theory of evolution by natural selection, let' s see what led up it.
People from prehistoric times could not help noticing the great variety of plants and animals in the world around them. Here in southern France some of the earliest humans about fifteen thousand years ago drew pictures on their cave walls of plants and animals important to their lives. For the most part people were too busy trying to survive in competition with these other living creatures to give much thought to why there were so many. Or to wonder how they got to be the way they were, in some ways like humans and in other ways 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 one particular kind of living creature, human beings.
In the ancient Greek Ionian cities (now in ruins on the western coast of modern Turkey) some of the world's first philosopher scientists dared to ask and answer questions like this in a different way.
Anaximander in 550 bc. proposed one of the first scientific theories of evolution to explain the variety and likenesses among living things. All life, he said, has come from eariy life in the water. Over long period of time, the water creatures crept out onto the land, developed legs, then fur and finally human form. Anaximander did not have much evidence to support his theory, nor did he have any idea just how this kind of near miracle could actually have taken place.
One of the handicaps early thinkers had was massive ignorance. They knew of only a tiny fraction of the variety of plants and animals 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 ofliving things have been described.)
It was not until the 18th century, about the same time the American colonies were beginning to change into the United States, that 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 animals never before known to westen naturalists.
A little earlier, a Dutch lens maker, Anton von Leeuwenhoek, found a way to view another new world no one had ever even glimpsed before - a microscopic wonder world- teeming with what he called his 'little beasties." The number and variety of known living creatures was growing by leaps and bounds! How to make sense of all this new knowledge?
One of the important early pioneers in biology to make a major start in this direction was a poor young man in Sweden, Carl Linnaeus. As a university student he went on a field trip to Lapland to conect plant and animal specimens. A few years after this 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 living things, one that is still being used today.
All living things, proposed Linnaeus, should be grouped according to a natural and logical system. Each kind of living thing should be given a unique double name in internationally accepted Latin. First would be its genus. Followed by its species. It was called a binomial nomenclaturesystem.
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.
Linnaeus brounht order and svstem to the growing science of the living world. He helped people see the reality of living species. He was, however, opposed to the idea that living species had evolved from common ancestors, one of the key concepts in theories of evolution.
Others of the 18th century, however, did begin to speculate on this possibility.
One of the most important was a Frenchman, Georges Buffon. A charming, elegant man of great wealth, Buffon was able to devote himself to scientific study without wony of earning a living. He founded one of the first genuine biological research centers in the world-the jardin du Roi (Garden of the King) in Paris.
In between many love affairs and a few duels, Buffon managed to write 44 volumes of natural history. These volumes summarized all that was then known about the natural world. In some of the these volumes he anticipated many of the ideas of Danvin and later evolutionists, but he never quite put together a convincing theory to explain how living things became so different and varied, nor why, at the same time, all living things had so much in common.
Buffon's books led the religious authorities, however, to dring him before the Syndic of the Sorbonne in 1751. They commanded that he 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 at about 100,000 years. Biblical doctrine held that the earth was created in 4004 B.C.
Another Frenchman, Jean Baptiste Lamarck, built upon 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 also executed Buffon and his aristocratic family).
Larmarck proposed a theory of evolution which he said reflected the natural order of animals in nature. Its key ideas were two: nature has an innate tendency to evolve in the direction of increasing complexity, and two, acquired characteristics will be passed on to offspring. In this way nature will slowly move toward increasing variety and complexity and will fill up all the niches of the living world.
Lamarck also has the distinction of being the first to coin and use the word "biology."
Paradoxically, one of Lamarck's most critical scientific opponents, the anti-evolutionist Georges Cuvier, laid even more important groundwork for the later flowering of the Darwinian evolution theory. This gToundwork built on a new look at the unusual forms of rock and bone called 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 at the Museum of Natural History in Paris 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. He became the world expert in reconstructing an entire animal from a few fossil bones. And he concluded from his study that fossils were the 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. Cuvier still believed in an earth of recent creation.
An opposite geological view was taken by the Scotsman generally given credit for being the father of modern geology, James Hutton. Hutton viewed the earth as much older than Cuvier, or Buffon. In fact, he saw the earth as having "no vestige of a beginning, no prospect of an end."
Hutton saw earth as changing very slowly over very long periods of time. He saw this change coming 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 his friend and contemporary, Charles Darwin.
By the mid 19th century, ideas about possible evolution of living forms were widespread, but no one had yet convincingly demonstrated how it could have happened. And here we come back to the man deserving the most credit for doing so the English gentleman, Charles Darwin.
Darwin as a child loved the out of doors. He loved hiking and hunting. He was an avid collector of insects, shells, rocks and other specimens from nature. He had as especially large collection of beetles.
It was only after his five-year long voyage on HMS Beagle, however, that his intelled caught fire and he began to think seriously about what he had for so long loved to see, to touch and to collect. As he wrote of his first views of South American animals and plants, "It was like giving a blind man eyes!"
He filled notebooks with detailed observations of these exciting new plants and animals. He made notes of where they were living-the geology, the climate, the surrounding plants and animals. He made collections of plant parts and animal skins and skeletons, of rocks and minerals. He carefully labelled and preserved everything for later study back home in England.
When Darwin did return to England in 1836 he married, had a large family and settled to a life of quiet study here in the small town of Down, just south of London.
Here in this study at Down he worked each morning, reviewing his notes, examining his specimens, reading what other scientists had observed in their travels and studies, and what they thought.
So many questions to answer. Questions like: why are the birds he found on one island in the Galapogos very similar but not the same as those he found on a nearby island? Why are the plants he found in one part of South American similar but different in interesting ways from the plants found in the South Pacific islands? What relation is there between the plants and animals he found on his trip and the fossil remains of plants and animals he also found on his trip?
And most important of all were the really big questions: Why are there so many different species of plants and animals anyway? And why, despite this incredible variety, are all living things so much alike-alike in their basic shucturesalike in their basic chemistry-alike in their ways of surviving and of reproducing?
As he thought about these questions, out of the thousands and hundred of thousands of details he had personally observed or read about, there slowly emerged a large simple pattern.
Perhaps it was on his daily noonday walks behind the house overlooking the quiet English countryside that his theory of evolution by natural selection took shape. As so often happens in science, at almost the same time Darwin came to this theory of natural selection another man was coming to much the same theory. That man was Alfred Russel Wallace.
When summarized, like most good scientific theories, the ideas of Danvin and Wallace are surprisingly simple. There are five major points.
One. Living creatures have more offspring than can possibly survive.
Two. There is variation in these offspring.
Three. Some variations give an advantage and some a disadvantage in an inevitable struggle for survival.
Four. Nature will select the most fit variations to survive in this struggle and these variations will be the ones to pass on the favored offspring.
Five. In this way living things will change over time. Given enough time, these changes will be so great that whole new species of living things will appear on the earth.
Darwin's book "On the Origin of Species by Means of Natural Selection" and his following book, "The Descent of Man" sold out before they were even printed. They made an immediate, a dramatic and a long-lasting impression on the world of science and of society. In these books he piled one piece of evidence on another to illustrate and to support his theory of natural selection. And this evidence was so overwhelming, it convinced most scientists around the world, then and now.
Not everyone was convinced of course, then or now. In his own day Darwin was ridiculed unmercifully from the pulpit and in the popular press. He was also criticized by some scientists.
Today although there is disagreement and uncertainty about some of the details of earth history and of Darwinian theory, there is also a very broad agreement on the overall theory. And like all good scientific theories, the theory of evolution by natural selection points the way to fruitful new areas of research on the living world of the past, the present and the future.
As to the past, one exciting area of research closely related to Darwin's theory of evolution is the history of dinosaurs. For instance:
A hundred and fifty million years ago you might have met a dinosaur around that next bend. Just a little over ten years ago an American physicist and his geologist son studied this rock face near Gubbio, Italy, and figured out why you won't meet any dinosaurs today.
What they found right here in this rock face was a thin layer that could be accurately dated at about 65 million years ago. In this thin layer of clay they found a surprisingly large amount of a rare element, iridium. This iridium helped them to come up with a plausible theory as to why the dinosaurs became extinct in such a short period of time after having roamed the earth for over 50 million years!
The iridium, they theorized, came from the global fallout when a giant meteor struck the earth 65 million years ago! Other lines of evidence pointed to a spot off the coast of what is now southern Mexico where the giant meteor hit the earth, sending out huge clouds of dust that blanketed the earth's atmosphere cutting off the sunlight for a few years. After over 100 million years of change in the world of dinosaurs this drastic alteration in the environment was too much for any variation to cope with and led to the extinction of all dinosaurs.
As to the present and future, for example, we can see evolution going on today with remarkable speed in the cases of disease causing bacteria changing to become immune to our latest antibiotic. We can see the changes in insects as their hereditary structures are modified to escape the harmful effects of our latest insecticide. And by using the theory of natural selection first clearly stated by Danvin, biologists and ecologists today can better know where to look and how to cope with these and other changes in the living environment today and tomorrow.
Although evolution by natural selection is accepted today by most professional scientists as one of the key scientific theories that help us make sense of the natural world, it is also still controversial.
On the one hand it is rejected, as it was in Darwin's time, by some religious groups as taking away from the Bibiical story of creation. On the other hand, it has been extended and used in modern times to both support and to denounce social movements like capitalism, socialism, communism, fascism, manifest density, progressive education, racism, sexism and more. Looking into these claims would take us far beyond the story in this program.
Looking back now with 20/20 hindsight, however, we can at the least see how wrong Darwin's father was. The young man who was good for nothing but shooting and rat-catching left the world of science and the world of society a different place.
"When on board HMS Beagle as naturalist, 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."