Saturday, January 9, 2021

Darwin's theory: Hard to swallow, then and now

Presented to the Club by Roger Linscott, about 1981

A century and a half ago, in the year 1831, a young divinity student of 22 set sail from England on a voyage to South America. Twenty-eight years later, after prolonged study and soul-searching, he wrote a book based upon his observations there. The world – certainly the world of science – has never been the same since.

The young man, of course, was Charles Darwin, and the book was The Origin of the Species. When he embarked on his historic voyage, he had already abandoned a proposed career in medicine, after fleeing in horror from a surgical theater in which an operation was being performed on an unanesthetized child, and was a rather reluctant candidate for the clergy, a career deemed suitable for the younger son of an English gentleman. An indifferent student, Darwin was an ardent hunter and horseman, a collector of beetles, mollusks and shells, and an amateur botanist and geologist. When the captain of the surveying ship H.M.S. Beagle, himself only three years older than Darwin, offered passage to any young man who would volunteer to go without pay as a naturalist, Darwin eagerly seized the opportunity to escape from Cambridge. Five years later, he returned to an inherited fortune, an estate in the English countryside, and a lifetime of independent study that radically changed mankind’s view of life and of our place in the living world.

To understand the extraordinary genius of Darwin’s theory of evolution, it is useful to look briefly at the intellectual climate in which it was formulated. Aristotle, the world’s first great biologist, believed that all living things could be arranged in a hierarchy – a ladder of nature in which the simplest creatures had a humble position on the bottommost rung, mankind occupied the top, and all other organisms had their proper places in between. Until the end of the century, most biologists believed in such a natural hierarchy; but whereas Aristotle thought that living organisms had always existed, the later biologists believed, in harmony with the teachings of the Old Testament, that all living things were the product of a divine creation. They believed, moreover, that most were created for the service or pleasure of mankind. Indeed, it was pointed out, even the lengths of day and night were planned to coincide with the human need for sleep.

That each type of living thing came into existence in its present form — specially and specifically created – was a compelling idea. How else could one explain the astonishing extent to which every organism was adapted to its environment and to its role in nature? It was not only the authority of the church but also, so it seemed, the evidence before one’s own eyes, that gave such strength to the concept of special creation.

Actually, it was geologists, more than biologists, who paved the way for overturning this concept. During the latter part of the 18th century, there was a revival of interest in fossils, which previously had been collected only as curiosities, regarded as stones that somehow looked like shells. The English surveyor William Smith, born 50 years before Darwin, was among the first to study the distribution of fossils scientifically. Whenever his work took him down into a mine or along canals, he carefully noted the order of the different layers of rock and collected the fossils from each layer. He eventually established that each stratum, no matter where he came across it in England, contained characteristic kinds of fossils.

Smith did not interpret his findings, but the implication that the present surface of the earth had been formed layer by layer over a very long period of time was unavoidable. This was a brand-new idea. Christian theologians, by counting the successive generations since Adam (as recorded in the Bible) had calculated the maximum age of the earth at about 6,000 years, and no one had ever thought in terms of a longer period. Yet the world described by William Smith was clearly a very ancient one. A revolution in geology was beginning; earth science was becoming the study of time and change, rather than a mere cataloging of types of rocks. As a consequence, the history of the earth became inseparable from the history of living organisms, as revealed in the fossil record.

Although the way to evolutionary theory was being prepared by the revolution in geology, the time was not yet ripe for a parallel revolution in biology. The dominating force in European science in the early 19th century was Baron George Cuvier, a French aristocrat who was the founder of vertebrate paleontology, or the scientific study of the fossil record. An expert in anatomy and zoology, he applied his special knowledge of the way in which animals are constructed to the study of fossil animals, and was able to make brilliant deductions about the form of an entire animal from a few fragments of bone. We think of paleontology and evolution as so closely connected that it is surprising to learn that Cuvier was a staunch and powerful opponent of evolutionary theories. He recognized the fact that many species that once existed no longer did – but he explained their extinction by postulating a series of catastrophes. After each catastrophe, the most recent of which he declared to be Noah’s Flood, new species filled the vacancies. Louis Agassiz, the great Harvard scholar and America’s leading 19th century biologist, was a similarly devout opponent of evolution. He contended that the fossil record revealed 50 to 80 total extinctions of life and an equal number of separate creations.

But the person who most directly influenced Darwin was Charles Lyell, a geologist who was twelve years his senior and whose books Darwin took with him on the Beagle. On the basis of his own observations, Lyell opposed the theory of catastrophes as an explanation for the creation of new species. He believed that the slow, steady and cumulative effect of natural forces had produced continuous change in the course of the earth’s history; and since this process is demonstrably slow, its results being barely visible in a single lifetime, it must have been going on for a very long time. Lyell was not an evolutionist. But what Darwin’s theory needed was the concept of vast amount of time – and it was time that Lyell gave him. The discovery that the earth was very ancient was the snowball that started the whole avalanche.

This, then, was the intellectual climate in which Charles Darwin set sail from England in 1831. As the Beagle moved down the Atlantic coast of South America, through the Straits of Magellan and up the Pacific coast, Darwin traveled the interior. He explored the rich fossil beds of South America, with the theories of Lyell fresh in his mind, and collected specimens of the many new kinds of plant and animal life he encountered. He was impressed most strongly by the constantly changing varieties of organisms he saw. The birds and animals on the west coast were very different from those on the east coast, and even as he moved slowly up the west coast, one species would give way to another.

Most interesting of all to Darwin were the animals and plants that inhabited the small, barren group of islands known as the Galapagos, off the coast of Ecuador. The islands had been named by the Spanish after their most striking inhabitants, the giant tortoises, some of which weight 220 pounds or more. Each of the islands has its own type of tortoise, and sailors who took these tortoises on board and kept them as a convenient source of fresh meat on their sea voyages could readily tell which island any particular tortoise had come from. Then there were groups of finchlike birds, thirteen species in all, that differed from one another in the sizes and shapes of their bodies and beaks, and particularly in the type of food they ate. In fact, though clearly finches, they had many features seen in completely different types of birds on the mainland.

From his knowledge of geology, Darwin knew that these islands, clearly of volcanic origin, were much younger than the mainland. Yet the plants and animals of the islands were different from those of the mainland, and in fact, the plants and animals of different islands of the archipelago differed from one another. Were the living things on each island the product of a separate special creation, Darwin wondered – or was it possible that from an original paucity of birds in the archipelago, one species had been taken and modified for different ends? This problem “continued to haunt him.”

Darwin was a voracious reader. Not long after his return to England, he came across a short but much talked-about sociological treatise by the Reverend Thomas Malthus, which first appeared in 1798. In this book, Malthus warned, as economists have warned frequently since, that the human population was increasing so rapidly that it would soon be impossible to feed all the earth’s inhabitants. Darwin saw that Malthus’s conclusion – that food supply and other factors hold populations in check – is true for all species, not just the human species. For example, Darwin calculated that a single breeding pair of elephants – which are among the slowest breeders of all animals – would, if all their progeny lived and reproduced the normal number of offspring over a normal life pan, produce a standing population of 19 million elephants in 750 years. Yet the average number of elephants remained the same over the years. So, although this single breeding pair could have, in time, produced 19 million elephants, it did, in fact, produce only two. But why these particular two? The process by which the two survivors are, so to speak, “chosen,” Darwin called natural selection.

Natural selection, according to Darwin, was a process analogous to the type of selection exercised by breeders of horses, cattle or dogs. In the case of artificial selection, we humans chose individual specimens of plants of animals for breeding on the basis of characteristics that seem to us desirable. In the case of natural selection, the environment takes the place of human choice. As individuals with certain hereditary characteristics survive and reproduce, and individuals with other hereditary characteristics are eliminated, the population will slowly change. If some horses were faster than others, for example, those would be more likely to survive, and their progeny, in turn, might be faster, and so on.

According to Darwin’s theory, these variations among individuals of a species, which occur in every natural population, are wholly a matter of chance. They are not produced by the environment, not by a creative force, not by the unconscious striving of the organism. In themselves, they have no goal or direction, It is the operation of natural selection over a series of generations that gives direction to evolution. A variation that gives an animal a slight advantage makes that animal more likely to leave surviving offspring. Thus, a giraffe, say, with a slightly longer neck has an advantage in feeding, and so is likely to leave more offspring than a giraffe with a shorter neck. If the longer neck is an inherited trait, some of these offspring will also have long necks, and if the long-necked animals in this generation have an advantage, the next generation will include more long-necked animals – and so on, until, finally the population of short-necked giraffes will have become a population of longer-necked ones, thought there will still be variations.

The extraordinary thing about Darwin’s formulation was not so much his espousal of evolution — which was an idea that had at least crossed other scientific minds before his – but rather, the crucial role he gave to chance variation as the great triggering mechanism of the evolutionary process – the thread that links together all the diverse phenomena of the living world. Species arise, he said, when differences between individuals within a group are gradually converted into differences between groups as the groups become separated in space and time.

It was a truly revolutionary concert that, in one fell swoop, brought biology out of the Middle Ages – out of the realm of theology and into the realm of science.

It also profoundly influenced our way of thinking about ourselves. With the possible exception of the storm that raged about Copernicus and Galileo, no revolution of scientific thought has had as much effect on human thought as this one. The major reason is, of course, that evolution is in flat contradiction to the lateral, fundamentalist interpretation of the Bible. The new astronomy had made it clear that the earth is not the center of the universe or even our own solar system. With Darwin, the new biology required acceptance of the proposition that, like all other organisms, we too are not created for any special purpose or as part of any universal design but instead rose in the course of the earth’s long history from earlier and more primitive forms.

The heretical dimensions of this proposition may explain why almost three decades elapsed between Darwin’s voyage on the Beagle and his publication of the Origin of the Species.

Two years after his return to England, he read the essay by Malthus, and in 1842 he wrote a preliminary sketch of his theory, which he revised in a 230-page manuscript in 1844. There is little doubt that he realized the magnitude of his accomplishment. On completing the revision, he wrote a formal letter to his wife requesting her, in the event of his death, to publish it – but then, with the manuscript and letter in safe-keeping, he turned to other work, including a four-volume treatise on the natural history of barnacles. For more than twenty years after his return from his voyage, Darwin mentioned his ideas on evolution only in his private notebooks and in letters to a few scientific colleagues.

In 1850, urged on by his friends Charles Lyell and botanist Joseph Hooker, Darwin set to work slowly preparing a manuscript for publication. In 1858, some ten chapters later, he received a bombshell in the form of a letter from another English naturalist, Alfred Russell Wallace, who was working in the Malay Peninsula and had corresponded with Darwin on several previous occasions. Wallace presented a theory of evolution that almost exactly paralleled Darwin’s own. Tossing in bed one night with a fever, Wallace had had a sudden flash of insight. “I saw at once,” he recollected, “that the ever-present variability of all living things would furnish the material from which, by the mere weeding out of those less adapted to the actual conditions, the fittest alone would continue the race.” Within two days, Wallace’s 20-page manuscript was completed and in the mail.

When Darwin received Wallace’s letter, he turned to his friends for advice, and Lyell and Hooker, taking matters into their own hands, presented the theory of Darwin and Wallace at a scientific meeting just one month later. Their presentation received little attention at the time, but for Darwin the floodgates were opened. He finished his long treatise in another few months, and the book was finally published. The first printing of 1,250 copies sold out the same day.

Why Darwin’s long delay? His own writings, voluminous thought they were, shed little light on this question. But perhaps his background does. When Darwin embarked on the Beagle, he was a devout Christian who did not doubt the literal truth of the Bible and did not believe in evolution any more than did the other English scientists he had met and whose books he had read. When he achieved his Malthusian insight a few years later, he was still in his 20s. He held no professional position, but he had acquired the admiration of his colleagues for his work aboard the Beagle. He was not about to compromise a promising career by promulgating a heresy that he might be unable to prove to their satisfaction. Perhaps more important, his wife, to whom he was deeply devoted, was extremely religious. In short, it seems reasonable to suppose that Darwin, as has been the case with others, found the implications of his theory difficult to confront.

Nor it is any wonder that he shrank from those implications for so long. Once the earth and its living inhabitants are seen as products of historical change, the theological philosophy embodied in the great chain of being ceases to make sense; the fullness of the world becomes not an eternal manifestation of God’s bountiful creativity but an illusion. For most of the world’s history, the vast majority of species on earth today did not exist and considerably less than one per cent of those that did exist do so today. If evolution has occurred, and if it has proceeded from the entirely natural causes Darwin envisioned, then the adaptations of organisms to their environment, the intricate construction of the bird’s wing and the orchid’s flower are evidence not of divine design but of the struggle for existence.

Moreover, and this may be the deepest implication of all, Darwin brought to biology, as his predecessors had brought to astronomy and geology, what has been termed the sufficiency of efficient causes. No longer was there any reason to look for final causes and goals. To the questions “What purpose does this species serve? Why did God make tapeworms?” the answer is, “To no purpose.” Tapeworms were not put here to serve a purpose, nor were plants, not plants, nor people. They came into existence not by design but by the action of utterly impersonal natural laws.

This was an exceedingly hard pill for most people to swallow – and it still is. The fact that the earth is not the center of the universe, though once considered heresy, is now accepted by the vast majority of mankind. The fact that man is descended of apes is not. Almost uniquely among the great scientific formulations of history, Darwinian theory remains a subject of bitter controversy more than a century after his death – not among biologists, who accept it with virtual unanimity, but among ordinary people who cannot bring themselves to face the possibility of a world that operates without a grand, divinely guided design.

Indeed, the hullabaloo over Darwinism is currently more intense – at least in the United States – than it has been since the 1920s when Clarence Darrow and William Jennings Bryan battled the issue in Dayton, Tennessee, at the celebrated Scopes trial. Leading the attack today are the so-called Creationists, who are mostly spokesmen for fundamentalist religious groups – but their popular support is wide and deep. In a recent Gallup Poll of cross-section Americans, nearly half of the respondents agreed with the statement: “God created men pretty much in his present form at one time within the past 10,000 years.” Thirty-eight per cent of the respondents agreed with an alternative statement: “Man has developed over millions of years from less advanced forms of life, but God guided this process, including man’s creation.” A mere nine per cent accepted a third choice – that man had developed from less advanced forms of life without diving intervention. Another public poll, published in Christian Century several years ago, similarly reported that approximately half the adults in America continue to believe that “God created Adam and Eve to start the human race.”

Armed with this kind of public support, the Creationists in recent years have been zeroing in on the public school system, particularly in the South and Southwest – not with the demand that the teaching of evolution be banned (which was the issue in the Scopes trial) but with the seemingly less dogmatic demand that Creationist doctrines should be given equal time with Darwinian theory in all science classrooms. They have been remarkably successful in this endeavor. In Dallas, Atlanta, and Chicago, not to mention countless smaller cities, school committees have yielded to the equal-time pressure. And perhaps more disturbing, national textbook publishers – whose profits depend on producing books that will be marketable in every part of the nation – have been soft-pedaling Darwinism in their biology texts or specifically including Creationism as an alternative and co-equal doctrine.

“Where will we be,” asks Stephen Jay Gould, the eminent Harvard biologist, “if any pressure group can win, by legislative fiat, the ordered inclusion of its favorite doctrine into school curricula?” It’s a good question. One is reminded of Lyndon Johnson’s story about the earnest young pedagogue who, in the depths of depression, applied for an opening as a science teacher in a backwater town in Texas. Confronting the local school board at his interview, he was asked by the grim-visaged chairman: “Do you teach that the earth is flat or that the earth is round?” The young man looked from face to face without seeing a hint of enlightenment. “Well,” he said, “I can teach it either way.”

The notion that one can teach the great unifying theory of modern biology “either way” is no less absurd.

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