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No Turning Back
The Extinction Scenario
By Richard Ellis
OPEN ROAD INTEGRATED MEDIACopyright © 2004 Richard Ellis
All rights reserved.
Extinction (Sort of) Explained
Standard textbooks on evolutionary biology and paleontology hardly mention extinction. Much is said about the origin of species and the evolution of species once they are formed, but discussions of extinction are usually limited to casual references and the enigma of the great mass extinctions. On causes of extinction we are apt to read, "Species become extinct when population sizes drop to zero," or "Species die out if they are unable to adapt to changing conditions." These statements are true, of course, but are virtually devoid of content.
—David Raup, 1991
Everybody knows what extinction is. The dictionary defines it as "the act of extinguishing, or, the fact of becoming extinguished or extinct." (Extinguish is in turn defined as "to put out a fire, a light, or to bring an end to.") More to our point, Thain and Hickman's Penguin Dictionary of Biology (1996) defines extinction as "Termination of a genealogical lineage. Used most frequently in the context of a species, but applicable also to populations and to taxa higher than species." Thus the fundamental precept of extinction is self-evident: a species (or population, genus, or family) is extinct when its last member has died.
Yet extinction theory is greatly complicated by a number of factors, among them the inability of biologists and paleontologists to agree on exactly what a species is. "Alarmingly," noted Purvis, Jones, and Mace (2000), "there are over 20 species concepts now in common use." For living animals, we recognize as separate species those that are morphologically similar but cannot interbreed. The same criterion obviously cannot be applied to fossils, so paleontologists have to make use of anatomical differences and similarities—when there is enough fossil material to make a determination.
In recent times, however, with the introduction of DNA analysis, what was long believed to be a single species can now be fragmented into two or more. Killer whales, the most widely distributed of all cetaceans, found from southern polar waters to the Arctic and many places in between, were once thought to be a single worldwide species—Orcinus orca. New observations and analyses have shown that there may be an Antarctic species that is quite different from its northern counterparts in coloration and behavior; it has been provisionally named O. glacialis. Where there were once believed to be six species of balaenopterid whales (blue, fin, sei, Bryde's, and two species of minke), two more were added as of 2003 (see pp. 254-55). The two distinct species of elephant—African and Asian—have been subdivided into three with the recent addition of the genetically distinct Bornean elephant; there may actually be as many as six different subspecies. The gorilla may indeed be not one (Gorilla gorilla) but two closely related species. In a New Scientist article dated November 22, 2003, Bob Holmes and Jeff Hecht wrote, "A new trend is to delineate species as evolutionarily separate lineages, including separated populations that are evolving in divergent ways. This has already happened for albatrosses. There are 13 recognized species, but the IUCN lists 21 threatened lineages." On the other hand, it has recently been shown that the animal known as the red wolf, which was once awarded the species name of Canis rufus, is not a separate species at all, but a hybrid of the gray wolf and the coyote.
Even if we are able to plug in an acceptable definition of a species, however, identifying the moment that it became extinct is much more problematic. For example, rumored sightings of such animals as the ivory-billed woodpecker and the Tasmanian tiger continue to circulate, and while these animals are generally considered extinct, it is impossible to state unequivocally that a few stragglers may not be found in their often inaccessible habitats. The 1938 discovery of the coelacanth, thought to have been extinct for 75 million years, is the paradigmatic case of a rediscovered "lost" animal, and the unexpected appearance of the previously unknown megamouth shark in Hawaiian waters in 1975 indicates how difficult it is to make categorical statements about existence or nonexistence. If it is so difficult with modern animals, imagine how hard it is to decide from fossil evidence alone that a particular species became extinct at a particular moment. There are no more trilobites, pterosaurs, or ichthyosaurs, but when did the last one die?
Extinction is one of the most powerful forces on earth, and one of the most enigmatic. It affects every species that has ever lived, and has eliminated most of them. In time, it will eliminate us too. Despite its tremendous importance, however, nobody is quite sure what it is or how it works. We know that there have been countless numbers of living things that have walked, run, crawled, flown, swam, or just remained stationary over the past 3 billion years, and that the great majority of them are gone; but beyond that, we know very little. The fossil record not only supports the all-encompassing theory of evolution, demonstrating conclusively that life changes over time, but it is also our primary evidence for extinction. Because so many creatures are no longer viable, extinction can be clearly read in the fossil record, although the actual evidence of evolution—"change over time"—is only infrequently revealed.
Until the nineteenth century, almost everybody—scientists included—accepted the traditional Christian view that the Bible was to be taken literally, and that God had made the sun, the moon, the earth, and the oceans. He also made all the mammals, birds, alligators, snakes, fishes, and insects, but his crowning achievement was "to make man in our own image, after our likeness; and let them have dominion over the fish of the sea, and over the fowl of the air, and over cattle, and over every creeping thing that creepeth upon the earth." Even Aristotle believed that the animals had been divinely arranged in a ladder, with humans confidently perched on the top rung, the epitome of life.
In the sixteenth century, there were only about 150 kinds of mammals known to Europeans, approximately the same number of birds, and perhaps thirty kinds of snakes. For the first edition of his Systema Naturae, published in 1735, Carolus Linnaeus, a Swedish botanist, categorized all the known creatures and plants into an arrangement in which every living thing was given a binomial name, corresponding to its genus and species. (He tried the same system with minerals, but it didn't work as well.) Linnaeus was born in 1707, so by the time he had developed his classification, he was able to include some newly discovered beasts; but he still firmly believed that all known species were unchanging creations of God, who had chosen to arrange things so that Man resided at the top of the pyramid. He is reputed to have said, "God created, but Linnaeus classified."
As human horizons widened, animals that Linnaeus never knew of began to appear. In North America, there were raccoons, pronghorns, grizzly bears, and mountain lions; South America had weird and wonderful monkeys, sloths, anteaters, llamas, and armadillos; and there was an entire continent in the southern sea populated by the strangest fauna of all: kangaroos, wallabies, wombats, koalas, and platypuses—mammals that raised their young in a pouch. The "dark continent" of Africa had giraffes, lions, zebras, baboons, chimpanzees, and gorillas, not one of which was mentioned in the Biblical story of the Great Flood. Whales and dolphins had been known to humans ever since they demonstrated their unfortunate inclination to beach themselves. Two thousand years ago, Aristotle wrote that "It is not known for what reason they run themselves aground on dry land; at all events, it is said that they do so at times, and for no obvious reason." Until whalers and other seafarers took to the sea, the only cetaceans that could be known were those that washed ashore.
True, Europeans had seen strange fossils since ancient Greece, which suggested that there were some life-forms that were no longer with us, but for European and American minds, this meant only that the Flood described in the Bible must have wiped out those species that Noah didn't load onto the Ark. (How the fishes, whales, and dolphins managed to board the Ark was never explained; maybe they swam along in its wake.)
Fossils—the word comes from the Latin fossilis, meaning "dug up"—originally referred to any natural object that was pulled out of the ground. The discovery of the first fossils has not been recorded, but Adrienne Mayor has written a book, The First Fossil Hunters, in which she suggests that when ancient Greeks, Romans, Persians, and Chinese found fossilized material they simply incorporated it into their mythology; one example is the ancestral giraffe (Samotherium) skull that appears almost intact on a black-figured vase that is believed to show Heracles fighting a legendary monster. To the ancients, extinction was not an issue; Mayor says they seamlessly placed the beasts represented by skulls of long-gone mammals and even dinosaurs into their legends and myths.
When fossilized shark teeth were first discovered on land, long before any were brought up from the oceans' depths, their origin was a complete enigma. Pliny, the great Roman student of nature, believed that they had fallen from the sky during eclipses of the moon. They were later thought to be the tongues of serpents that St. Paul had turned to stone while he was visiting the island of Malta; in consequence they acquired the name glossopetrae ("tongue stones"). They were believed to have magical properties, especially as counteragents to the bites of poisonous snakes; to that end they were often worn as talismans.
In 1565, the Swiss zoologist Konrad Gesner wrote On Fossil Objects, a little book that included everything from gemstones and crystals to ammonites, belemnites, and sharks' teeth. However, Gesner hardly differentiated the fossils from one another, and did not concern himself with what had happened to the animals who originally occupied his "organic" fossils. Robert Hooke (1635-1703), the British architect who helped rebuild London after the Great Fire of 1666, who described the shadow made on Saturn by the planet's rings, and who made a map of the moon's craters, has been described as "London's Leonardo" (Bennett et al. 2003), because like the more famous Italian polymath, he understood and described certain phenomena long before anyone else. Like Leonardo da Vinci, he was an instrument maker; he specialized in clockwork mechanics, devising the spiral spring in watches. However, Hooke is not as well known as Leonardo or his own contemporary Isaac Newton, because, as Richard Stone (2003) wrote, "set against the brilliance of Isaac Newton, Hooke has tended to shine like a 60-watt lightbulb." It did not help Hooke's reputation that Newton "denied many of Hooke's contributions and tried to obliterate them from history." Recently, with new books being published on Hooke's substantial accomplishments, and symposia convened to discuss his contributions, his reputation is on the ascendant. Hooke believed, wrote Stone, "that the biblical flood could not be taken literally." He also wrote, "There have been many other Species of Creatures in former Ages of which we can find none at present"; in other words, he recognized the concept of extinction long before anyone else.
In 1695, John Woodward (1665-1728), a teacher of physics at Gresham College in London, published his Essay Toward the Natural History of the Earth: and Terrestrial Bodies, especially Minerals: as also of the Seas, Rivers and Springs. With an Account of the Universal Deluge: and of the Effects that it had upon the Earth. Woodward espoused the idea that Noah's Flood had not only changed the face of the earth, it had created fossils as well. For some of Woodward's contemporaries, including the Danish naturalist Nicolaus Steno, fossils showed that momentous changes had taken place over time, with mountains thrown up and land conveyed from one place to another. For Woodward, the fossils demonstrated that the planet had been completely reconfigured by the Flood. "The Terraqueous Globe," he wrote, "is to this Day nearly in the same Condition that the Universal Deluge left it; being also likely to continue so till the Time of its final Ruin and Dissolution, preserved to the same End for which 'twas first formed."
Woodward believed that the floodwaters had receded with such violence that great mountains and valleys were raised up or gouged out; what we now know as fossils were actually organisms forced into the stone by the violence of the waters. Among his supporters was Baron Gottfried von Leibniz (1646-1716), better known as a mathematician and philosopher. Leibniz believed in the Flood, but recognized that so much water could not have come from rain alone. He proposed that the water had been contained in hollows within the earth, and squeezed out to flood the planet. But it was a Swiss physician named Johann Jacob Scheuchzer (1672-1733) who would become the most prominent advocate of the deluge theory; in 1708, he wrote Piscium querelae et vindiciae ("Complaints and Justifications of the Fishes"), in which he argued—through the voice of a Latin-speaking fish—that fossils are the remains of various sea creatures that had been carried to the mountains by the Flood.
Except perhaps to Robert Hooke, the origin of fossils was a complete mystery to everyone during the seventeenth and eighteenth centuries, but there was no shortage of explanations for the mysterious appearance of various animal forms in places where their presence could not be easily explained, such as fishes on mountaintops. The Victorian naturalist Philip Gosse maintained that fossils were strewn around by God as part of the spontaneous creation of a complete world; evidence of a history that had never really occurred. A God who could make something as intricate as a man would have no trouble with a few stony bones that resembled a fish. Others believed that it was just coincidence that the fossils resembled living animal and plant forms; they had never actually been alive. Almost everybody, however, subscribed to the idea that when Noah's Flood submerged the earth, all the animals were brought aboard the ark, and it was their descendants—and only their descendants—that populated the earth. To have believed otherwise would have been sacrilegious.
However, this dogmatic view of the Gospel truth was beginning to change. In The Map That Changed the World (2001), Simon Winchester wrote:
In addition it had not escaped the notice of some collectors that many of the figured stones they found represented animals and plants that did not seem currently to exist. This suggested, in other words, that if indeed the stones were relics, they were relics of living creatures that were no longer around and had since become extinct. Since extinction was an impossible, unthinkable event in any divinely created cosmos, then this notion too was invalid, inappropriate, and wholly wrong.
In other words, it was difficult enough to understand how unknown animals could somehow be turned to stone, or why seashells might appear on mountaintops, but it was nearly impossible for early philosophers to comprehend that God's mercy might include the whimsical elimination of some of his creations from the face of the earth. The very concept of extinction presented an almost undecipherable conundrum.
Excerpted from No Turning Back by Richard Ellis. Copyright © 2004 Richard Ellis. Excerpted by permission of OPEN ROAD INTEGRATED MEDIA.
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