No Turning Back: The Life and Death of Animal Speciesby Richard Ellis
Nearly every species that has lived on earth is extinct. The last of thedinosaurs was wiped out after a Mount Everest-sized meteorite slammedinto the earth 65 million years ago. The great flying and marine reptiles areno more. Before humans crossed the Bering Land Bridge some 15,000 yearsago, North America was populated by mastodons, mammoths, saber-toothedtigers,
Nearly every species that has lived on earth is extinct. The last of thedinosaurs was wiped out after a Mount Everest-sized meteorite slammedinto the earth 65 million years ago. The great flying and marine reptiles areno more. Before humans crossed the Bering Land Bridge some 15,000 yearsago, North America was populated by mastodons, mammoths, saber-toothedtigers, and cave bears. They too are MIA. The passenger pigeon, once themost numerous bird in North America, is gone forever.
In No Turning Back, renowned naturalist Richard Ellis explores the lifeand death of animal species, immortalizing creatures that were driven toextinction thousands of years ago and those more recently. He documentsthose that were brought back from the brink, and most surprisingly, he revealsanimals not known to exist until the twentieth century an antidoteto extinction.
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No Turning Back
The Life and Death of Animal Species
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. 25455). 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 ivorybilled 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 dif- ficult 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 everybodyscientists 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. No Turning Back
The Life and Death of Animal Species. Copyright © by Richard Ellis. Reprinted by permission of HarperCollins Publishers, Inc. All rights reserved. Available now wherever books are sold.
Meet the Author
Richard Ellis is recognized as one of America's foremost writers and painters on marine natural history. Among his many books are The Book of Sharks, The Book of Whales, Dolphins and Porpoises, The Search for the Giant Squid, Great White Shark, Imagining Atlantis, and The Empty Ocean. He lives in New York City.
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