Why Darwin’s still a scientific hotshot

Editor’s Note:

Nobel laureate James D. Watson, co-discoverer of the molecular structure

of DNA, has edited and provided commentary for a new anthology of Charles Darwin’s four major books, collected in one volume by Running Press. Watson’s essay introducing “Darwin: The Indelible Stamp: The Evolution of an Idea” is excerpted here.

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I first became aware of Charles Darwin and evolution while still a schoolboy growing up in Chicago. My father and I had a passion for bird-watching and when the snow or the rain kept me indoors, I read his bird books and learned about evolution. We also used to frequent the great Field Museum of Natural History, and my fragmentary knowledge of evolution helped guide me through the myriad specimens in the museum. It is extraordinary the extent to which Darwin’s insights not only changed his contemporaries’ view of the world but also continue to be a source of great intellectual stimulation for scientists and nonscientists alike. His “On the Origin of Species” was rightly praised by biologist Thomas Henry Huxley as “ ... the most potent instrument for the extension of the realm of natural knowledge which has come into men’s hands since the publication of Newton’s “Principia.”

When Darwin returned from his five-year voyage aboard the H.M.S. Beagle, he turned over his various collections to experts on birds, beetles, mollusks and the like. John Gould was Darwin’s bird expert. Darwin was surprised to learn from him that the finches he had collected on the Galapagos Islands closely resembled similar birds on the South American continent some 600 miles away, yet the finches of one island were different from those of the other islands. Why, Darwin wondered, would Galapagos finches resemble those of the nearest continent if each finch had been created independently? (The same was true on the Cape Verde Islands off the coast of Africa; the animals resembled those of the African continent.) The logical answer was that the islands had been populated by birds that had found their way from South America, blown, perhaps, by strong winds. How, then, had these birds on different islands in the Galapagos come to differ from one another? They did so by evolving through adaptation to different niches, so that some developed bills for crushing seeds, others for eating insects, and still others for collecting nectar from plants. Evolution provided a much more parsimonious explanation than special creation.

“What can be more curious,” Darwin wrote in “Origin,” “than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?”

Richard Owen, the great English anatomist and an implacable enemy of Darwin and evolutionary ideas, had pronounced that such homologies -- similarities that suggest a common origin -- revealed the handiwork of a creator who, perhaps, saved time and effort by simply varying an archetype. But this made little sense, this tinkering and adjusting. Surely a creator could have done a better job at creating an efficient flying mammal, say by giving feathered wings to the bat?

“How inexplicable are these facts on the ordinary view of creation!” Darwin exclaimed. “Nothing can be more hopeless than to attempt to explain this similarity ... by utility or by the doctrine of final causes.” What did make sense of this whole class of facts was Darwin’s evolutionary perspective -- the similarities of form suggested descent with modification from a common ancestor.

Although “Origin” provided overwhelming evidence for evolution, Darwin left two important questions, acknowledging each as major difficulties for his theory. He could not explain what gave rise to the variations observed in organisms or how these and other traits were transmitted from generation to generation. He faced these problems head-on in 1868 in “Variation of Animals and Plants Under Domestication.” Darwin speculated that during a process he called “pangenesis,” all parts of the body released “gemmules” that accumulated in the germ cells. But his speculation did not survive experiments carried out by Francis Galton, Darwin’s cousin. Galton tried to change the color of white and black rabbits by transmitting gemmules between them using blood transfusions, but without effect. In his autobiography, Darwin referred to pangenesis as “my well-abused hypothesis.” It is one of the great missed opportunities of science: Darwin was unaware that a contemporary, Gregor Mendel, had already laid the foundations for the scientific analysis of heredity.

The work of the population geneticists took Mendelian concepts and applied them to populations of organisms, which put Darwin’s ideas of 100 years earlier on a firm scientific basis. But it took three naturalists -- Julian Huxley (T.H. Huxley’s grandson), geneticist Theodosius Dobzhansky (who worked with fruit fly geneticist Thomas Hunt Morgan) and Ernst Mayr (then at the American Museum of Natural History in New York) -- to produce a more biologically based account of this stage of evolutionary thought. Huxley captured the moment in the title of his book “Evolution -- The Modern Synthesis.” At long last there was a reasonably complete integration of evolution, genetics and natural selection.

This was how matters stood when I entered the University of Chicago in 1943 to become a zoologist, inspired by my bird-watching and trips with my father to the Field Museum. Population geneticist Sewall Wright taught at Chicago and he became my first scientific hero. I sat in on two of his classes, one on evolution, the other on physiological genetics. It was in the latter that I first learned of Oswald Avery’s finding that DNA appeared able to transmit hereditary properties between two different types of pneumococcus bacteria. It was at about that time that Erwin Schrodinger -- one of the founders of quantum mechanics -- published a little book, “What Is Life?” I came across it in the biology department library in my third year, in 1946. “What Is Life?” is one of those books that changes lives, and mine, along with those of several other peers, changed irrevocably. Schrodinger recognized that the key element of heredity had to be the transfer of genetic information in the form of a molecule from generation to generation. My passion for birds seemed misplaced when one of the great questions of the 20th century was still unanswered: What was the nature of the gene, the essence of life? And, although I did not think in these terms then, what was the chemistry on which natural selection and evolution depended?

It may astonish those who think that evolutionary studies are carried out in the dusty rooms of museums amid all those specimens collected so many years ago, that the most impressive data supporting the laws of evolution come from the studies of the past 40 years in molecular genetics. The clearest evidence for the common ancestry of all living organisms comes from the universality of the genetic code, which provides the translation between the information in a gene and the protein encoded by that gene. With some variations, this code is the same for viruses, bacteria, worms, human beings, beetles, mice and slugs. The most extreme example is that bacteria can be given a human gene and they will make a human protein. What an extraordinary vindication of Darwin’s ideas!

Darwin would have been thrilled to learn that the same set of 25,000 to 30,000 genes is present in most animals. Almost every gene in our DNA has a homologous gene in the DNA of other mammals, such as the mouse. It is even more extraordinary when we look at more distantly related organisms; the invertebrate sea squirt, for example, has only half our number of genes, but as many as two-thirds of these have homologues in human DNA.

Darwin had not anticipated that “Origin” would find an audience beyond the scientific elite, his peers. And yet the first printing of the book sold out at the pre-publication sale, with no fewer than one-third being bought by Mudie’s Circulating Library, an endorsement equivalent to a recommendation today from Oprah Winfrey. The book, in short, was a sensation for the general public, and with good reason. Copernicus, Galileo and Newton had removed the Earth from its central position in the universe, although there was yet a grandeur in the ways the planets swept through space, and the regularities of their movements revealed the hand of the Creator. But the position of Man, as the image of God on Earth, was left unchanged by their revisions of the received cosmology. Darwin changed this. Although he made only the cryptic remark in “Origin” -- “Much light will be thrown on the origin of man and his history” -- his readers were under no illusion of the consequences of accepting evolutionary arguments for the origin of man.

Today, there is a concerted effort by some religion-dominated scientists to treat evolution as a theory, as though that in some way diminishes its authority and power as an explanation of how the world works. Fortunately, the courts are exercising their wisdom and rejecting arguments of equal time for creationist beliefs in schools. We can only hope that a time will soon come when rational, skeptical thought renders the creationists’ stories as what they are -- myths.

One of the greatest gifts science has brought to the world is continuing elimination of the supernatural, and it was a lesson that my father passed on to me, that knowledge liberates mankind from superstition. We can live our lives without the constant fear that we have offended this or that deity who must be placated by incantation or sacrifice, or that we are at the mercy of devils or the Fates. With increasing knowledge, the intellectual darkness that surrounds us is illuminated and we learn more of the beauty and wonder of the natural world.

Let us not beat about the bush -- the common assumption that evolution through natural selection is a “theory” in the same way as string theory is a theory is wrong. Evolution is a law (with several components) that is as well substantiated as any other natural law, whether the law of gravity, the laws of motion or Avogadro’s law. Evolution is a fact, disputed only by those who choose to ignore the evidence, put their common sense on hold and believe instead that unchanging knowledge and wisdom can be reached only by revelation. *