The Third Chimpanzee: The Evolution and Future of the Human Animal Read online

  This view of ancient environmental destruction is supported by both ancient writings and modern archaeology. One example is Petra, a “lost city” carved in rock—and known to movie fans because part of Indiana Jones and the Last Crusade was filmed there.

  Petra was clearly a wealthy and powerful city. It flourished for hundreds of years as a trade center and was well known in Roman times. How did it support itself in a bleak desert landscape, and why was it abandoned and forgotten? Paleobotanists studying pollen and other preserved plant materials have learned that Petra once stood in a woodland. As in Chaco Canyon, residents gathered firewood and cut timber. They also grazed goats, which ate small trees. Pollen grains from 900 AD show that by that time two-thirds of the trees had disappeared. Even shrubs and grasses had declined. The ravaged land surrounding Petra could no longer support a major city.

  Petra is just one of many ancient cities around the world that stand today as monuments to states that destroyed their means of survival. Whole civilizations, such as the Maya of Central America and the Harappan culture of India and Pakistan, may have collapsed because their growing populations overwhelmed their environments. History books often dwell on kings and barbarian invasions, but in the long run, deforestation and erosion may have done more to shape the course of human history.

  ANSWERS IN MIDDENS

  BY STUDYING CENTURIES-OLD PLANT REMAINS, paleobotanists gained a picture of the changing types of plants that grew around Chaco Canyon and Petra over long periods of time. This is how we know that forested areas changed to shrubland, then desert. But how did the scientists get ahold of centuries-old pollen and plant fibers? They relied on small plant-eating animals that gather vegetation and store it in underground shelters called middens.

  Little rodents called pack rats were the midden builders of Chaco Canyon. Although each pack rat midden is usually abandoned after fifty or a hundred years of use, bits of vegetation stored by generations of pack rats remain behind. In dry desert conditions, those bits of plant material remain well preserved for centuries. Scientists can use radiocarbon techniques to date each midden, which is like a time capsule, preserving samples of the local vegetation from the time the midden was in use.

  Petra, an ancient city in the country of Jordan.

  Petra never had pack rats, but it does have middens. Rabbit-size mammals called hyraxes live in the Middle East. Like pack rats, hyraxes store their food (plant materials) in underground middens. Old hyrax middens at Petra contained samples of up to a hundred different plant species. These samples told scientists what type of habitat existed when each midden was being used by animals that lived at the same time as ancient civilizations. Animal middens turned out to be a valuable source of information about the history of both habitats and humans.

  Environmentalism Past and Future

  The supposed golden age of environmentalism looks more and more like a myth. But we do know that some modern people who live outside industrial society practice good conservation. We also know that not all species have been exterminated, and not all habitats have been destroyed, so the golden age couldn’t have been all dark.

  Small, long-established societies where everyone is more or less equal tend to evolve conservationist practices. They’ve had plenty of time to get to know their local environment and to see how it’s in their best interest to take care of it. Damage is more likely to occur when people suddenly colonize an unfamiliar environment, as the Maoris and the Easter Islanders did, or when they advance along a frontier, which lets them simply move on to a new environment when they’ve destroyed the one behind them.

  Damage also occurs when people acquire a new technology with destructive powers they haven’t had time to understand—this is happening now in New Guinea, where pigeon populations are being devastated by shotguns. Damage is also likely in big centralized states where power is concentrated in the hands of rulers who are out of touch with their environment. Finally, some species and habitats are more vulnerable to damage than others. Flightless birds with no fear of humans were easy prey. Dry, fragile environments such as the American Southwest and the Mediterranean Sea region were easily degraded.

  What practical lessons can we learn from knowing how earlier people wiped out species and ruined resources? Government planners might be guided by the past. The American Southwest has more than one hundred thousand acres of pinyon-juniper woodland that we are using more and more for firewood. Unfortunately, the U.S. Forest Service has little information to help it decide how much wood can be taken without destroying the woodland. Yet the Anasazi already tried the experiment, and it failed. Woodland still hasn’t recovered in Chaco Canyon after more than eight hundred years. Paying archaeologists to determine how much firewood the Anasazi consumed would be cheaper than making the same mistake and ruining a hundred thousand acres of woodland, as we may now be doing.

  It’s always been hard for humans to know the rate at which they can harvest biological resources for a long time without using them up. By the time the signs of decline are clear enough to convince everyone, it may be too late to save the species or habitat in question. The Maoris who consumed New Zealand’s moas and the Anasazi who killed off pinyon-juniper woodland were not guilty of moral failure. Instead, they failed to solve a really difficult ecological problem.

  There are two big differences between us and those involved in the tragic ecological failures of the past. We have scientific knowledge that they lacked, and we have the means to communicate and share what we know. We can read all about the ecological disasters of the past. Yet we continue to hunt whales and clear tropical rain forest as if no one had ever hunted moas or cleared pinyon-juniper woodland. If the past was a golden age of ignorance, the present is an iron age of willful blindness.

  Standing more than twelve feet tall, this Columbian mammoth skeleton may be the largest in the world. Until it became extinct around 10,000 years ago, this species roamed the plains of North America—and was hunted by the early human inhabitants of the continent, who used spears to bring down mammoths and other big game.

  CHAPTER 15

  BLITZKRIEG AND THANKSGIVING IN THE NEW WORLD

  THE UNITED STATES DEVOTES TWO NATIONAL holidays, Columbus Day and Thanksgiving, to celebrating the European “discovery” of America. No holidays celebrate the much earlier discovery of the Americas by the ancestors of the Indians. Yet archaeology suggests that, for sheer drama, the earlier discovery dwarfs the adventures of Christopher Columbus and the Pilgrims of Plymouth Rock. Within perhaps no more than a thousand years, Indians found a way through an Arctic ice sheet and swept all the way to Patagonia, at the southern tip of South America. At the end of that time they had populated two productive and unexplored continents.

  The Indians’ march southward was the greatest expansion of our species’ range in the history of Homo sapiens. Nothing like it can ever happen again. It was marked by another drama: a mass extinction. When the first hunters arrived, they found the Americas teeming with big mammals that are now extinct: elephant-like mammoths and mastodons, three-ton ground sloths, beavers the size of bears, and sabertoothed cats, plus lions, cheetahs, camels, horses, and more.

  What happened when humans met these beasts? Archaeologists and paleontologists disagree. The interpretation that makes the most sense to me is a “blitzkrieg”—a lightningfast assault in which the animals were quickly exterminated by humans, perhaps in just ten years at any given site. If that view is correct, it would have been the quickest and most severe extinction of big animals since the dinosaurs disappeared. It would also have been the first of many blitzkriegs that marred our mythical golden age of environmental innocence.

  The Greatest Expansion in Human History

  The confrontation between animals and the first people in the Americas was the last act in a long epic of human expansion. Spreading out of their center of origins in Africa, humans expanded into Asia and Europe, and then from Asia to Australia. This left North and South America as the
last habitable continents without people. So how and when did people get to the Americas?

  From Canada to the southern tip of South America, Indians look more like one another than the inhabitants of any other continent. They must have arrived here too recently to have evolved much genetic diversity. At the same time, American Indians resemble certain East Asian peoples. The evidence from both archaeology and genetics proves that Native Americans originated from Asia. The easiest route from Asia to America is across the Bering Strait, a narrow strip of water that separates Siberia and Alaska. Between twenty-five thousand and ten thousand years ago, during the Ice Age, sea levels were lower all over the world because so much water was locked up in ice. At that time, Siberia was linked to Alaska by a land bridge that is now under the Bering Strait.

  Colonizing the Americas needed more than a land bridge. It also needed people to be living at the Asian end of the land bridge, in Siberia. Because of its harsh climate, the Siberian Arctic was not colonized until late in human history. But by twenty thousand years ago, mammoth hunters were living there, leaving stone tools and other traces of their presence. And stone tools similar to those of the Siberian hunters have been found in Alaska, dating from around twelve thousand years ago.

  Once they had reached present-day Alaska, the Ice Age hunters found themselves separated from what is now the United States by another barrier. A broad ice cap stretched across Canada. Then, around twelve thousand years ago, a narrow, ice-free corridor opened up just east of the Rocky Mountains. We know that hunters soon moved south through that ice-free corridor, because their stone tools have turned up in archaeological sites south of the ice cap. At that point the hunters met America’s great beasts, and the drama began.

  Archaeologists call these pioneering ancestral Indians the Clovis people because their stone tools were first recognized at a site near Clovis, New Mexico. Since then, Clovis tools or ones similar to them have been found throughout North America. These tools are much like the ones used by earlier eastern European and Siberian hunters, but with the addition of grooves on both sides of the stone spear points. These grooves made it easier to tie the stone points to sticks, but we don’t know whether the hunters threw their weapons or stabbed with them. Somehow, though, the hunters drove the points into big mammals hard enough to penetrate bone. Scientists have dug up mammoth and bison skeletons with Clovis points inside them.

  The Clovis people spread quickly. The known sites in the United States were occupied for just a few centuries, just before eleven thousand years ago. Then Clovis points were replaced by smaller, more finely made tools called Folsom points. (These were discovered near Folsom, New Mexico.) These points are found with bison bones but never with mammoth bones.

  Why did hunters switch from the Clovis spear points to the smaller Folsom points? Maybe they no longer needed the big points, because the biggest game animals were gone. There were no mammoths left. Camels, horses, giant ground sloths, and other big mammals had disappeared as well. Both North and South America lost large numbers of big mammal species at the same time.

  As the human population has grown since 1800 (measured on the right), the number of species becoming extinct has steadily increased (shown on the left). The parallel lines raise the question: How many of these modern extinctions have humans caused?

  Many paleontologists blame the extinctions on climate and habitat change at the end of the Ice Age. Yet the end of the Ice Age brought more habitat for animals, not less, as melting ice opened up areas of forest and grassland. Anyway, the big American mammals had already survived the ends of at least twenty-two earlier ice ages. In addition, both warmth-loving and cold-loving species went extinct, which should not have been the case if the cause was climate change.

  Paul Martin of the University of Arizona described the outcome of hunter-meetsmammals as a blitzkrieg. In his view, the first hunters to emerge from the ice-free corridor thrived and multiplied because they found an abundance of big-game animals that had no fear of humans and were easy to hunt. When game was killed off in one area, the hunters and their offspring fanned out into new areas and killed the mammal populations there. By the time the hunters had reached southern South America, most big mammal species of the Americas had been exterminated.

  First in the Americas

  Martin’s blitzkrieg theory has drawn vigorous criticism. Doubters ask: Could a small band of hunters passing through the ice-free corridor breed fast enough to populate two continents in a thousand years? Could they cover the eight thousand miles to southern South America in that time? Were Clovis hunters really the first people in the Americas? And could they have killed millions of big animals so efficiently that not a single individual of many species survived?

  In modern times, when colonists have settled an uninhabited island, their population has grown as rapidly as 3.4 percent a year. This growth rate—four children per couple, and a new generation every twenty years—would multiply 100 hunters into 10 million in only 340 years. To reach the tip of South America in 1,000 years, humans would have had to expand southward an average distance of 8 miles a year, an easy task. Some migrations of Africa’s Zulu people in the nineteenth century are known to have covered 3,000 miles in 50 years.

  As for whether the Clovis people were the first humans to spread south of the Canadian ice sheet, that’s a harder question. It’s also extremely controversial among archaeologists. Dozens of sites have been believed by a few researchers to contain evidence of human remains earlier than the Clovis people, but none of these supposed pre-Clovis sites is accepted without question by the whole scientific community.

  In contrast, the evidence for the Clovis culture is undeniable, found in many places, and widely accepted. At site after site, archaeologists find a layer of Clovis tools with the bones of large extinct species. Above the Clovis layer is a younger layer of Folsom tools, but no bones of large mammals except bison. Below the Clovis layer lie thousands of years’ worth of fossils of large extinct mammals, but no human tools or remains. It makes good sense to me that the Clovis people were the first Americans.

  MEADOWCROFT AND MONTEVERDE: UNANSWERED QUESTIONS

  SOME ARCHAEOLOGISTS CLAIM TO HAVE FOUND evidence of human presence in the Americas before the time of the Clovis people. Almost all these claims raise questions about whether the material used for radiocarbon dating was mixed with older material, whether the dated material was actually found with human remains, or whether tools supposedly made by humans are really just naturally shaped rocks.

  The two most nearly convincing of the claimed “pre-Clovis” sites are Meadowcroft Rockshelter in Pennsylvania, dated to about sixteen thousand years ago, and Monte Verde in Chile, South America, dated to at least thirteen thousand years ago. Monte Verde has many types of wellpreserved human artifacts, but the radiocarbon dating of these artifacts is open to question. At Meadowcroft there has been debate about whether the radiocarbon dates are accurate, especially because plant and animal species from the site are not thought to have lived there until much more recently than sixteen thousand years ago. Until questions about Monte Verde and Meadowcroft can be answered with more certainty, the Clovis people should be considered the oldest definitely known inhabitants of the Americas.

  Exterminating the Mammoths

  Another hotly debated argument about the blitzkrieg theory concerns the overhunting and extermination of big mammals. It seems hard to imagine Stone Age hunters killing mammoths at all, much less hunting them to extinction. Yet we know that Stone Age hunters who lived in what is now Ukraine, south of Russia, regularly killed mammoths—and built their houses out of neatly stacked mammoth bones. Picture a band of early American hunters spearing a terrified mammoth ambushed in a narrow streambed. Such hunts must have taken place many times.

  Remember that the big mammals of the Americas had probably never seen humans before the Clovis hunters. Animals that evolved without humans around are surprisingly tame and unafraid. When I visited New Guinea’s isolated F
oja Mountains, which have no human population, I found the large tree kangaroos so tame that I could approach within a few yards of them. Probably the big mammals of the Americas were killed off before they could evolve a fear of humans.

  Could Clovis hunters have killed mammoths fast enough to exterminate them? Modern elephants are slow breeders that take about twenty years to reproduce their numbers. Prehistoric mammoths probably bred slowly, too. Few other large animal species breed fast enough to reproduce their numbers in less than three years. It could have taken Clovis hunters only a few years to kill off the large mammals in a given area and then move on to the next area.

  The Clovis hunters probably killed often, too. A mammoth might have 2,500 pounds of meat, but to use all that meat would mean preserving it by drying it. Would you go to the work of drying a ton of mammoth meat when you could just go kill another mammoth? Hunters probably used only part of the meat from each kill, along with other desirable parts such as skins and tusks.

  We are all too familiar with the blitzkriegs by which modern European and American hunters nearly wiped out bison, whales, seals, and many other large animals. We also know that similar blitzkriegs occurred on oceanic islands when earlier hunters reached unoccupied lands. How could it have been different when the Clovis hunters entered an unoccupied New World?

  Cattle graze where forest was recently cleared for pastureland in the Amazon rain forest. Around the world, livestock grazing is a major contributor to deforestation and habitat loss.