The Third Chimpanzee: The Evolution and Future of the Human Animal Page 16

  What about the view that humans lived in a state of ecological balance before the Industrial Revolution, and that only in modern times have we exterminated species and overused our environment? The remaining chapters examine this idea. We will look first at the belief in a golden age when humans supposedly lived in harmony with nature. Then we’ll look more closely at one of the biggest, most dramatic, and most controversial mass extinctions: the disappearance of many large mammals from the Americas, just as humans arrived. Finally, we’ll try to determine how many species we have already driven to extinction, and what that might mean for our own future.

  CHAPTER 14

  THE GOLDEN AGE THAT NEVER WAS

  WHEN EUROPEANS BEGAN TO SETTLE THE Americas, the air and rivers were pure, the landscape was green, and the Great Plains teemed with bison. Today we breathe smog, worry about toxic chemicals in our drinking water, pave over the landscape, and rarely see a large wild animal. Things are sure to get worse as more species go extinct and the pollution of our air and seas continues.

  Two simple reasons go a long way toward explaining our worsening mess. One is that modern technology has far more power to cause havoc than the simple stone axes of the past. The other is that far more people are alive now than ever before. But there may be a third factor: a change in attitudes. Unlike modern city-dwellers, people who live outside industrial economies depend on their local environment for survival, and at least some of them understand and revere it. A New Guinea tribesman once explained to me, “It’s our custom that if a hunter one day kills a pigeon in one direction from the village, he waits a week before hunting for pigeons again, and then goes in the opposite direction.” We’re only beginning to realize that many so-called primitive peoples practice sound conservation policies.

  Environmentalists who are sickened by the damage that industrial societies are doing to the world often look to the past as a Golden Age, when everyone lived like those New Guinea tribesmen, in harmonious balance with the natural world. Until recently, I and many of my environmentalist colleagues shared this nostalgic view. That’s why recent discoveries by archaeologists and paleontologists have come as something of a shock. It’s now clear that preindustrial societies have been exterminating species, destroying habitats, and undermining their own existence for thousands of years.

  If these discoveries are correct, can we use them as case histories to predict our own fate? Can these recent findings explain some mysterious collapses of ancient civilizations, such as those of Easter Island or the Maya?

  New Zealand Minus Moas

  New Zealand is a Pacific Ocean island country east of Australia. When British colonists began settling there in the nineteenth century, they found no native land mammals except bats. They did, though, find the bones and eggshells of large birds. These birds had already become extinct, but the Maori people—Polynesians who had settled New Zealand centuries earlier— called them moa.

  Moas were ostrich-like birds. The largest species were ten feet tall and weighed up to five hundred pounds. Moas fed on twigs and leaves, making them New Zealand’s bird version of plant-eating mammals such as deer and antelope. Other bird species had disappeared before Europeans arrived. Some were big and flightless, including a large duck and an enormous goose. These flightless birds were descended from birds that had flown to New Zealand and then evolved to lose their wings. (They did not need wings because there were no humans or other mammal predators in New Zealand to hunt them.) Other little animals native to New Zealand had also become extinct or almost extinct, including frogs, snails, giant crickets, and strange mouselike bats that rolled up their wings and ran.

  Fossils show that moas had survived on New Zealand for millions of years. Why did they finally become extinct? And when? Were the moas and other native creatures still alive when the ancestors of the Maoris arrived around 1000 AD?

  When I first visited New Zealand, in 1966, people believed that the moas had died out because of a change in the climate. Any that had been alive when the first Maoris showed up must have been on their last legs. The Maoris were believed to be conservationists who could not have exterminated the moas. But three sets of discoveries overturned this idea.

  First, the Ice Age ended in New Zealand around ten thousand years ago. After that, the climate was more favorable to moas. The last moas died full of food and enjoying the best climate they had seen for thousands of years.

  Second, bird bones from Maori archaeological sites have been dated. They prove that all known moa species were abundant when the first Maoris stepped ashore. So were many other bird species now known only from fossil bones. Within a few centuries, they were extinct. It would be an incredible coincidence if dozens of species occupied New Zealand for millions of years and then happened to die out just when humans arrived.

  Third, more than a hundred large archaeological sites are known where Maoris cut up large numbers of moas, cooked them in earth ovens, and threw out the remains. They ate the meat, used the skins for clothing, made fishhooks and jewelry from the bones, and blew the contents out of eggs to use the shells for carrying water. The vast number of moa skeletons says that the Maoris were slaughtering these big birds for many generations.

  It is now clear that the Maoris exterminated moas, partly by killing them, partly by robbing their nests of eggs, and probably also by killing some of the forest in which the moas lived. Other bird species were exterminated as well.

  What about New Zealand’s smaller creatures— the crickets, snails, and bats? Deforestation may be part of the reason they went extinct, but the main reason was the other hunter the Maoris accidentally brought with them: rats! Just as moas evolved without humans and had no defenses against them, small creatures that had evolved in a rat-free environment were defenseless against these rodents.

  When the first Maoris landed, they found a New Zealand full of creatures so strange that we would think they were science-fiction fantasies if we did not have their fossilized bones. It was like reaching another planet on which life had evolved. Within a short time, much of New Zealand’s biological community had collapsed. Some of what remained died out in a second collapse following the arrival of Europeans. Today New Zealand has about half the bird species that greeted the Maoris, and many of the survivors are either at risk of extinction or limited to islands with few mammal pests. A few centuries of hunting had ended millions of years of moa history.

  Madagascar’s Vanished Giants

  Polynesians were not the only prehistoric exterminators. Halfway around the world from New Zealand is the world’s fourth-largest island, Madagascar, off the coast of Africa. Its people, the Malagasy, are descended from seafaring Indonesians who crossed the Indian Ocean to trade with East Africa and settled the island between one and two thousand years ago.

  Madagascar is home to many species found nowhere else, including two dozen species of small, monkey-like primates called lemurs. Littering Madagascar’s beaches are eggshells the size of soccer balls, proof of vanished giant birds. The eggs were laid by half a dozen species of extinct flightless birds up to ten feet tall. Similar to ostriches and moas but more massive, these extinct creatures are now called elephant birds. Fossil bones show that Madagascar also once had a number of vanished large mammals and reptiles. Among them were giant tortoises, lemurs as large as gorillas, and a hippopotamus the size of a cow.

  The bones of all these extinct species are known from fossil sites only a few thousand years old. Since they evolved and survived for millions of years before then, it is unlikely that all these extinct animals gave up the ghost just before hungry humans showed up. In fact, the elephant birds may have hung on long enough to become known to Arab traders, giving rise to the giant bird called the roc in the tale of Sindbad the Sailor.

  Certainly some if not all of Madagascar’s vanished giants were exterminated by the activities of the early Malagasy. Unintended actions, though, probably killed more big animals than hunters did. Fires that humans started to kill for
est for pasture would have destroyed the animals’ habitats, as would the grazing of cattle and goats. Dogs and pigs introduced by humans would have preyed on ground-dwelling animals, their young, and their eggs. By the time Portuguese explorers arrived around 1500, Madagascar’s once-abundant elephant birds had been reduced to eggshells covering the beaches, skeletons in the ground, and vague memories of rocs.

  The Easter Island Question

  The so-called Golden Age was tarnished by more than the extermination of species. Early human societies also destroyed habitats. One dramatic example is Easter Island, which lies in the Pacific about 2,300 miles west of the South American nation of Chile.

  An aura of mystery has clung to Easter Island ever since it and its Polynesian inhabitants were “discovered” by a Dutch explorer in 1722. There, on one of the world’s most isolated scraps of land, people had carved hundreds of statues out of volcanic rock. The statues weighed up to eightyfive tons and measured as much as thirty-seven feet in height. Without metal or wheels, using no power source except human muscle, the islanders had carried many of these statues to platforms several miles from where the stone was quarried. Other statues had been left unfinished or abandoned, as if the carvers and movers had suddenly walked off their jobs. Many statues were still standing when the Dutch explorer arrived, but by 1840 the islanders had pushed them all over. How were these huge statues made and moved? Why did the islanders stop carving them and eventually topple them over?

  To answer the first question, living Easter Islanders showed twentieth-century researcher Thor Heyerdahl how their ancestors used log rollers to move the statues. The answer to the second question lies in the island’s grim history, revealed by archaeological and paleontological research. When Polynesians settled Easter Island around 400 AD, the island was covered by forest, which the settlers gradually cleared, for timber and to plant gardens. By around 1500 the human population had grown to about 7,000. The islanders had carved about a thousand statues and raised at least 324 of them.

  But the forest had been destroyed so completely that not a single tree survived.

  Carving stopped because the islanders no longer had the logs needed to move and raise the statues. But deforestation also brought starvation. Without trees, the soil eroded, and gardens became less productive. Without trees, the islanders could not build canoes for fishing. Island society collapsed in a holocaust of war and cannibalism, scattering spear points across the land. Rival clans pulled down each other’s statues, and people lived in caves for selfprotection. What had once been a lush island supporting a remarkable civilization became the Easter Island of today: a barren grassland littered with fallen statues, supporting less than a third of its former population.

  Enormous statues gaze out over the wastes of Easter Island, where a oncethriving culture collapsed after the islanders cut down the forests.

  “MYSTERY ISLANDS” OF THE PACIFIC

  HENDERSON ISLAND IS AN EXTREMELY REMOTE speck of land in the tropical Pacific Ocean. Made of jungle-covered coral, riddled with crevices, it is totally unsuited for agriculture. It has been uninhabited ever since Europeans first saw it in 1606. That’s why it was a big surprise when paleontologists identified the bones of three species of pigeons and three species of seabirds that had gone extinct on Henderson between five hundred and eight hundred years ago. Fossils of the same six species, or their close relatives, had already been found on islands inhabited by Polynesians, where it was clear how they could have been exterminated by people. But how could they have gone extinct on uninhabited Henderson?

  The mystery was solved by the discovery of archaeological sites on Henderson, proving that Polynesians had lived there for several hundred years before Europeans ever saw the island. These islanders lived on pigeons, seabirds, and fish, until they wiped out the bird populations. With their food supply destroyed or greatly reduced, they either starved to death or abandoned the island. The Pacific contains at least eleven other “mystery islands” besides Henderson. These islands were found uninhabited by Europeans, but archaeological evidence shows that Polynesians had formerly lived there—sometimes for several centuries. All these islands were small or poorly suited to farming. Their inhabitants depended on birds and other animals for food.

  We know that early Polynesians overused and exterminated birds and wild animals in Hawaii and other islands where they lived for long periods. If they did the same thing on the small “mystery islands,” these specks in the ocean may represent the graveyards of human populations that destroyed their own resource base.

  Islands and Continents

  Polynesia and Madagascar are examples of the waves of extinction that probably washed over all large islands after the first human settlers arrived. Islands where life evolved without humans used to have unique species of big animals that modern zoologists never saw alive. Mediterranean islands such as Crete and Cyprus had pygmy hippos and giant tortoises, dwarf elephants and dwarf deer. The West Indies lost ground sloths, a bear-sized rodent, and owls of several sizes: normal, giant, colossal, and titanic. Small creatures such as lizards, frogs, snails, and birds disappeared, too—thousands of species lost, when you add up all the islands in the oceans.

  Paleontologist Storrs Olson has called these island extinctions “one of the swiftest and most profound biological catastrophes in the history of the world.” We won’t be sure that humans were responsible for all of it until the bones of the last animals and the remains of the first people have been dated more exactly for every island, as has already been done for Polynesia and Madagascar.

  The continents may have seen their own extinction waves, but in the more distant past. About eleven thousand years ago, around the likely time that the first ancestors of the American Indians reached the Americas, most large mammals became extinct throughout North and South America. Debate has raged over whether these species were done in by Indian hunters or just happened to perish by climate change around the same time. In the next chapter, I’ll explain why I think hunters did it. But it is much harder to pinpoint dates and causes for events that happened around eleven thousand years ago than it is for recent events, such as the moaversus- Maori collision within the past thousand years. Within the past fifty thousand years, for example, Australia was colonized by the ancestors of today’s Aborigines and lost most of its species of big animals. We do not yet know if the arrival of humans caused the extinctions.

  We can be fairly sure that the first people to reach islands created disaster for island species. The jury is still out, though, on the question of whether this also happened on continents.

  Anasazi Apocalypse

  Our second case of habitat destruction before the modern industrial era involves one of the most advanced Indian civilizations in North America. When Spanish explorers reached what is today the U.S. Southwest, they found gigantic multistory dwellings called pueblos standing empty in the middle of treeless desert. One of them, the 650-room pueblo at Chaco Culture National Historical Park in New Mexico, was five stories high, 670 feet long, and 315 feet wide. It was the largest structure ever built in North America until the steel skyscrapers of the late nineteenth century. The Navajo who lived in the area knew of the vanished builders only as Anasazi, meaning “the Ancient Ones.”

  The building of the Chaco pueblos started soon after 900 AD. Sometime in the twelfth century, just two hundred years later, people stopped living in them. Why did the Anasazi erect a city in a barren wasteland? Where did they get their firewood and the two hundred thousand wooden beams that supported their roofs? And why did they abandon the city?

  The usual view was that the Anasazi abandoned Chaco Canyon because of a drought. A different story, though, is told by the plants of Chaco, and how they changed over time. Paleobotanists are scientists who study plant remains from the past. When they examined plant remains from around Chaco, they learned that when the pueblos were built, they were not surrounded by desert. Instead, they stood in the middle of a woodland of short pinyon
and juniper trees, with a forest of taller ponderosa pine trees nearby. This was the source of the Anasazi firewood and timber.

  As people continued to live at Chaco, however, the woodland and forest were cleared until the environment became the treeless wasteland it remains today. People had to go at least ten miles for firewood, and much farther to find timber big enough for building. They made an elaborate road system to haul spruce and fir logs from mountains more than fifty miles away, using only their own muscle power.

  The deforestation around the pueblos caused increasing soil erosion and water runoff. The irrigation channels that the Anasazi dug to bring water to their fields carved out deeper and deeper gullies, until, at last, the groundwater may have dropped below the level of the fields, making it impossible to channel water into them. Without irrigation, the Anasazi couldn’t grow crops. Drought may have contributed to the Anasazi abandonment of Chaco Canyon, but a selfinflicted ecological disaster was another factor.

  Ecological Collapse in the Cradle of Civilization

  Another ecological collapse—this time around the city of Petra, in the Middle Eastern kingdom of Jordan—sheds light on why the power center of ancient civilization kept shifting. Many crucial developments in human culture arose in the Middle East, including agriculture, animal domestication, writing, imperial states, and battle chariots. With the overthrow of Persia (now Iran) by Alexander the Great, the center of power in the ancient world shifted from the Middle East to Greece. Later it shifted again, to Rome, and later again, to western and northern Europe. Why did each powerful region or state eventually lose its position at the center?

  One good theory is that each ancient center of civilization in turn ruined its resource base. The Middle East and the lands around the Mediterranean Sea were not always the dry, barren, overused landscape that appears today. In ancient times much of the area was a lush mosaic of wooded hills and fertile valleys. Human populations cut forests, cleared steep slopes for farming, overgrazed too many livestock, and planted crops too close together for the soil to recover. The result each time was soil erosion, flooding, crop failure, and the collapse of local human society.