Asimov's New Guide to Science

by Isaac Asimov

  The next year Darwin’s book was finally published. Its full title is On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. We know it simply as The Origin of Species.

  The theory of evolution has been modified and sharpened since Darwin’s time, through knowledge of the mechanism of inheritance, of genes, and of mutations (see chapter 13). It was not until 1930, indeed, that the English statistician and geneticist Ronald Aylmer Fisher succeeded in showing that Mendelian genetics provides the necessary mechanism for evolution by natural selection. Only then did evolutionary theory gain its modern guise.

  Naturally, advances in other branches of science continued to sharpen and focus the Darwinian concept. An understanding of plate tectonics (see chapter 4) explained a great deal concerning the forces that drive evolution and the manner in which similar species appear in widely separated parts of the earth. The ability to analyze proteins and nucleic acids in detail has made it possible to trace molecular evolution and, to judge from the degree of differences among molecules (as I will describe later in the chapter), the degree of relationship among organisms.

  Naturally, in anything so complex as evolutionary development of living organisms over billions of years of time, controversy continues about the details of the mechanism. Thus, in the 1970s, such biologists as Stephen Jay Gould have advanced the notion of punctuated evolution. They do not picture evolutionary development as a slow, more or less evenly and continually moving process. Rather, they feel that there are long periods of relative changelessness interspersed by situations in which comparatively sudden and pronounced changes occur (not overnight, but perhaps over a few hundred thousand years, which is fast on the evolutionary scale).

  Nevertheless, no reputable biologist feels any doubt about the validity of the evolutionary concept. Darwin’s basic point of view has stood firm; and indeed, the evolutionary idea has been extended to every field of science—physical, biological, and social.

  OPPOSITION TO THE THEORY

  The announcement of the Darwinian theory naturally blew up a storm. At first, a number of scientists held out against the notion. The most important of these was the English zoologist Richard Owen, who was the successor of Cuvier as an expert on fossils and their classification. Owen stooped to rather unmanly depths in his fight against Darwinism. He not only urged others into the fray while remaining hidden himself, but even wrote anonymously against the theory and quoted himself as an authority.

  The English naturalist Philip Henry Gosse tried to wriggle out of the dilemma by suggesting that the earth had been created by God complete with fossils to test human faith. To most thinking people, however, the suggestion that God would play juvenile tricks on humankind seemed more blasphemous than anything Darwin had suggested.

  Its counterattacks blunted, opposition within the scientific world gradually subsided and, within the generation, nearly disappeared. The opponents outside science, however, carried on the fight much longer and much more intensively. The Fundamentalists (literal interpreters of the Bible) were outraged by the implication that human beings might be mere descendants from an apelike ancestor. Benjamin Disraeli (later to be prime minister of Great Britain) created an immortal phrase by remarking acidly: “The question now placed before society is this, ‘Is man an ape or an angel?’ I am on the side of the angels.” Churchmen, rallying to the angels’ defense, carried the attack to Darwin.

  Darwin himself was not equipped by temperament to enter violently into the controversy, but he had an able champion in the eminent biologist Thomas Henry Huxley. As “Darwin’s bulldog,” Huxley fought the battle tirelessly in the lecture halls of England. He won his most telling victory in 1860 in a famous debate with Samuel Wilberforce, a bishop of the Anglican Church, a mathematician, and so accomplished and glib a speaker that he was familiarly known as “Soapy Sam.”

  Bishop Wilberforce, after apparently having won the audience, turned at last to his solemn, humorless adversary. As the report of the debate quotes him, Wilberforce “begged to know whether it was through his grandfather or his grandmother that [Huxley] claimed his descent from a monkey.”

  While the audience roared with glee, Huxley whispered to a neighbor, “The Lord hath delivered him into my hands”; then he rose slowly to his feet and answered: “If, then, the question is put to me, would I rather have a miserable ape for a grandfather, or a man highly endowed by nature and possessing great means and influence, and yet who employs those faculties and that influence for the mere purpose of introducing ridicule into a grave scientific discussion—I unhesitatingly affirm my preference for the ape.”

  Huxley’s smashing return apparently not only crushed Wilberforce but also put the Fundamentalists on the defensive. In fact, so clear was the victory of the Darwinian viewpoint that, when Darwin died in 1882, he was buried, with widespread veneration, in Westminster Abbey, where lie England’s greats. In addition, the town of Darwin in northern Australia was named in his honor.

  Another powerful proponent of evolutionary ideas was the English philosopher Herbert Spencer, who popularized the phrase survival of the fittest and the word evolution—a word Darwin himself rarely used. Spencer tried to apply the theory of evolution to the development of human societies (he is considered the founder of the science of sociology). His arguments were invalid, however, for the biological changes involved in evolution are in no way similar to social changes; and, contrary to his intention, they were later misused to support war and racism.

  In the United States, a dramatic battle against evolution took place in 1925; it ended with the anti-evolutionists winning the battle and losing the war.

  The Tennessee legislature had passed a law forbidding teachers in publicly supported schools of the state from teaching that humans had evolved from lower forms of life. To challenge the law’s constitutionality, scientists and educators persuaded a young high-school biology teacher named John Thomas Scopes to tell his class about Darwinism. Scopes was thereupon charged with violating the law and brought to trial in Dayton, Tennessee, where he taught. The world gave fascinated attention to his trial.

  The local population and the judge were solidly on the side of anti-evolution. William Jennings Bryan, the famous orator, three times unsuccessful candidate for the Presidency, and outstanding Fundamentalist, served as one of the prosecuting attorneys. Scopes had as his defenders the noted criminal lawyer Clarence Darrow and associated attorneys.

  The trial was for the most part disappointing, for the judge refused to allow the defense to place scientists on the stand to testify to the evidence behind the Darwinian theory, and restricted testimony to the question whether Scopes had or had not discussed evolution. But the issues nevertheless emerged in the courtroom when Bryan, over the protests of his fellow prosecutors, volunteered to submit to cross-examination on the Fundamentalist position. Darrow promptly showed that Bryan was ignorant of modern developments in science and had only a stereotyped Sunday-school acquaintance with religion and the Bible.

  Scopes was found guilty and fined one hundred dollars. (The conviction was later reversed on technical grounds by the Tennessee Supreme Court.) But the Fundamentalist position (and the State of Tennessee) had stood in so ridiculous a light in the eyes of the educated world that the anti-evolutionists were forced on the defensive and retired into the background for half a century.

  But the forces of darkness and ignorance are never permanently defeated; and in the 1970s, the anti-evolutionists returned for a new and even more insidious stand against the scientific view of the universe. They abandoned their earlier (at least forthright) stand on the literal words of the Bible, which had been totally discredited, and pretended to scientific respectability. They spoke vaguely of a “Creator” and were careful not to use the words of the Bible. They then argued that evolutionary theory was full of flaws and could not be true and that, therefore, creationism was true.

  To demonstrate that evolutiona
ry theory was not true, they did not hesitate to misquote, distort, take out of context, and in other ways violate the biblical injunction against false witness. And even so they proclaimed their own view as true only by default and never, at any time, have presented rational evidence in favor of their creationism, which they solemnly (but ridiculously) call “scientific creationism.”

  Their demand is that their foolish viewpoint be given “equal time” in the schools, and that any teacher or school textbook that discusses evolution should also discuss “scientific creationism.” At this writing, they have won no battles in the courts of the land; but their spokesmen, backed by earnest churchgoers who know no science, and to whom everything outside the Bible is a misty fog of ignorance, bully school boards, libraries, and legislators into censorship and suppression of science.

  The results may be sad indeed, for the creationist view that the earth is only a few thousand years old, as is the entire universe—that life was created suddenly with all its species distinct from the start—makes utter nonsense out of astronomy, physics, geology, chemistry, and biology and could create a generation of American youngsters whose minds are shrouded in the darkness of night.

  EVIDENCE FOR THE THEORY

  One of the arguments of the creationists is that no one has ever seen the forces of evolution at work. That would seem the most nearly irrefutable of their arguments, and yet it, too, is wrong.

  In fact, if any confirmation of Darwinism were needed, it has turned up in examples of natural selection that have taken place before our eyes (now that we know what to watch for). A notable example occurred in Darwin’s native land.

  In England, it seems, the peppered moth exists in two varieties, a light and a dark. In Darwin’s time, the white variety was predominant because it was less prominently visible against the light lichen-covered bark of the trees it frequented. It was saved by this protective coloration, more often than were the clearly visible, dark variety, from those animals that would feed on it. As England grew more industrialized, however, soot killed the lichen cover and blackened the tree bark. It was then the dark variety that was less visible against the bark and was protected. Therefore, the dark variety became predominant—through the action of natural selection.

  In 1952, the British Parliament passed laws designed to clean the air. The quantity of soot declined, the trees regained some of their light lichen covering, and at once the percentage of the light variety of moth began to increase. All this change is quite predictable by evolutionary theory, and it is the mark of a successful theory that it not only explains the present but can predict the future.

  The Course of Evolution

  A study of the fossil record has enabled paleontologists to divide the history of the earth into a series of eras. These were roughed out and named by various nineteenth-century British geologists, including Lyell himself, Adam Sedgwick, and Roderick Impey Murchison. Those named eras start some 600 million years ago with the first unmistakable fossils (when all the phyla except Chordata were already established). The first fossils do not, of course, represent the first life. For the most part, it is only the hard portions of a creature that fossilize, so the clear fossil record contains only animals that possessed shells or bones. Even the simplest and oldest of these creatures are already far advanced and must have a long evolutionary background. One evidence of that assumption is that, in 1965, fossil remains of small clamlike creatures were discovered and seem to be about 720 million years old.

  Paleontologists can now do far better. It stands to reason that simple one-celled life must extend much farther back in time than anything with a shell; and indeed, signs of blue-green algae and of bacteria have been found in rocks that were 1 billion years old and more. In 1965, the American paleontologist Elso Sterrenberg Barghoorn discovered minute bacteriumlike objects (microfossils) in rocks over 3 billion years old. They are so small, their structure must be studied by electron microscope.

  It would seem then that chemical evolution, moving toward the origin of life, began almost as soon as the earth took on its present shape some 4.6 billion years ago. Within a billion years, chemical evolution had reached the stage where systems complicated enough to be called living had formed. At this time, Earth’s atmosphere was still reducing and contained no significant quantity of oxygen (see chapter 5). The earliest forms of life must therefore have been adapted to this situation, and their descendants survive today.

  In 1970, Carl R. Woese began to study in detail certain bacteria that exist only under circumstances where free oxygen is absent. Some of these reduce carbon dioxide to methane and are therefore called methanogens (“methane producers”). Other bacteria engage in other reactions that yield energy and support life but do not involve oxygen. Woese lumps them together as archaeobacteria (“old bacteria”) and suggests that it might be well to consider them a separate kingdom of life.

  Once life was established, however, the nature of the atmosphere began to change—very slowly, at first. About two and a half billion years ago, blue-green algae may have already been in existence, and the process of photosynthesis began the slow change from a nitrogen-carbon-dioxide atmosphere into a nitrogen-oxygen atmosphere. By about a billion years ago, eukaryotes may have been well established, and the one-celled life of the seas must have been quite diversified and included distinctly animal protozoa, which would then have been the most complicated forms of life in existence—monarchs of the world.

  For 2 billion years after blue-green algae came into existence, the oxygen content must have been very slowly increasing. As the most recent billion years of Earth’s history began to unfold, the oxygen concentration may have been 1 percent or 2 percent of the atmosphere, enough to supply a rich source of energy for animal cells beyond anything that had earlier existed. Evolutionary change spurted in the direction of increased complication; and by 600 million years ago, there could begin the rich fossil record of elaborate organisms.

  The earliest rocks with elaborate fossils are said to belong to the Cambrian age; and the entire 4-billion-year history of our planet that preceded it has been, until recently, dismissed as the pre-Cambrian age. Now that the traces of life have unmistakably been found in it, the more appropriate name Cryptozoic eon (Greek for “hidden life”) is used, while the last 600 million years make up the Phanerozoic eon (“visible life”).

  The Cryptozoic eon is even divided into two sections: the earlier Archeozoic era (“ancient life”), to which the first traces of unicellular life belong; and the later Proterozoic era (“early life”).

  The division between the Cryptozoic eon and the Phanerozoic eon is extraordinarily sharp. At one moment in time, so to speak, there are no fossils at all above the microscopic level; and at the next, there are elaborate organisms of a dozen different basic types. Such a sharp division is called an unconformity, and an unconformity leads invariably to speculations about possible catastrophes. It seems there should have been a more gradual appearance of fossils, and what may have happened is that geological events of some extremely harsh variety wiped out the earlier record.

  ERAS AND AGES

  The broad divisions of the Phanerozoic eon are the Paleozoic era (“ancient life”), the Mesozoic (“middle life”), and the Cenozoic (“new life”). According to modern methods of geological dating, the Paleozoic era covered a span of perhaps 350 million years; the Mesozoic, 150 million years; and the Cenozoic, the last 50 million years of the earth’s history.

  Each era is in turn subdivided into ages. The Paleozoic begins, as I have stated, with the Cambrian age (named for a location in Wales—actually an ancient tribe that occupied it—where these strata were first uncovered). During the Cambrian period shellfish were the most elaborate form of life. This was the era of the trilobites, primitive arthropods of which the modern horseshoe crab is the closest living relative. The horseshoe crab, because it has survived with few evolutionary changes for 200 million years, is an example of what is sometimes rather dramatically called
a living fossil.

  The next age is the Ordovician (named for another Welsh tribe). This was the age, between 450 million and 500 million years ago, when the chordates made their first appearance in the form of graptolites, small animals living in colonies and now extinct. They are possibly related to the balanoglossus, which, like the graptolites, belongs to the hemichordata, the most primitive subphylum of the chordate phylum.

  Then came the Silurian (named for still another Welsh tribe) and the Devonian (from Devonshire). The Devonian age, between 350 million and 400 million years ago, witnessed the rise of fish to dominance in the ocean, a position they still hold. In that age, however, came also the colonization of the dry land by life forms. It is hard to realize, but true, that during five-sixths or more of its history, life was confined to the waters, and the land remained dead and barren. Considering the difficulties represented by the lack of water, by extremes of temperature, by the full force of gravity unmitigated by the buoyancy of water, it must be understood that the spread to land of life forms that evolved to meet the conditions of the ocean was the greatest single victory won by life over the inanimate environment.

  The move toward the land probably began when competition for food in the crowded sea drove some organisms into shallow tidal waters, until then unoccupied because the bottom was exposed for hours at a time at low tide.

  As more and more species crowded into the tidewaters, relief from competition could be attained only by moving farther and farther up the shore, until eventually some mutant organisms were able to establish themselves on dry land.

  The first life forms to manage the transition were plants. This took place about 400 million years ago. The pioneers belonged to a now extinct plant group called psilopsids—the first multicellular plants. (The name comes from the Greek word for “bare,” because the stems were bare of leaves, a sign of the primitive nature of these plants.) More complex plants developed; and by 350 million years ago, the land was covered with forest. Once plant life had begun to grow on dry land, animal life could follow suit. Within a few million years, the land was occupied by arthropods, molluscs, and worms. All these first land animals were small, because heavier animals, without an internal skeleton, would have collapsed under the force of gravity. (In the ocean, of course, buoyancy largely negated gravity, which was not therefore a factor. Even today the largest animals live in the sea.) The first land creatures to gain much mobility were the insects; thanks to their development of wings, they were able to counteract the force of gravity, which held other animals to a slow crawl.