The Rise and Fall of the Third Chimpanzee

by Jared Diamond

  That is not to say that all these Hawaiian birds were hunted out of existence. Although geese probably were indeed exterminated by overhunting, like the moas, small songbirds are more likely to have been eliminated by rats that arrived with the first Hawaiians, or else by destruction of forests that Hawaiians cleared for agriculture. Similar discoveries of extinct birds at archaeological sites of early Polynesians have also been made on Tahiti, Fiji, Tonga, New Caledonia, the Marquesas Islands, Chatham Islands, Cook Islands, Solomon Islands, and Bismarck Archipelago.

  An especially intriguing collision of birds and Polynesians took place on Henderson Island, an extremely remote speck of land lying in the tropical Pacific Ocean 125 miles east of Pitcairn Island, which is in turn famous for its own isolation. (Recall that Pitcairn is so remote that the mutineers who wrested the H.M.S. Bounty from Captain Bligh lived undetected on Pitcairn for eighteen years until the island was rediscovered.) Henderson consists of jungle-covered coral riddled with crevices and totally unsuitable for agriculture. Naturally, the island is now uninhabited and has been ever since Europeans first saw it in 1606. Henderson has often been cited as one of the world’s most pristine habitats, totally unaffected by humans.

  It was therefore a big surprise when Olson and fellow paleontologist David Steadman recently identified bones of two large species of pigeons, one smaller pigeon, and three seabirds that had become extinct on Henderson some time between 500 and 800 years ago. The same six species or close relatives had already been found in archaeological sites on several inhabited Polynesian islands, where it was clear how they could have been exterminated by people. The apparent contradiction of birds also being exterminated by humans on uninhabited, seemingly uninhabitable Henderson was solved by the discovery there of former Polynesian sites with hundreds of cultural artifacts, proving that the island had actually been occupied by Polynesians for several centuries. At those same sites, along with the bones of the six bird species that were exterminated on Henderson, were the bones of other bird species that survived, plus many fish.

  Those early Polynesian colonists of Henderson evidently subsisted mainly on pigeons, seabirds, and fish until they had decimated the bird populations, at which point they had destroyed their food supply and either starved or else abandoned the island. The Pacific contains at least eleven other ‘mystery’ islands, besides Henderson, which were uninhabited on European discovery but showed archaeological evidence of former occupation by Polynesians. Some of these islands had been settled for hundreds of years before their human population finally died out or left. All were small or in other respects marginally suitable for agriculture, leaving human settlers heavily dependent on birds and other animals for food. Given the widespread evidence for over-exploitation of wild animals by early Polynesians, not only Henderson but the other mystery islands as well may represent the graveyards of human populations that ruined their own resource base.

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  Lest I leave the impression that Polynesians were in any way unique as pre-industrial exterminators, let’s now jump nearly halfway around the globe to the world’s fourth largest island, Madagascar, lying in the Indian Ocean off the coast of Africa. When Portuguese explorers arrived around 1500 AD, they found Madagascar already occupied by people now called the Malagasy. On geographic grounds, you might have expected their language to be related to African languages spoken a mere 200 miles to the west, on the coast of Mozambique. Astonishingly, though, it actually proved to belong to a group of languages spoken on the Indonesian island of Borneo, on the opposite side of the Indian Ocean thousands of miles to the northeast. Physically, the Malagasy range in appearance from typical Indonesians to typical blacks of East Africa. These paradoxes are due to the Malagasy having arrived between 1,000 and 2,000 years ago, as a result of Indonesian traders voyaging around the Indian Ocean coastline to India and eventually to East Africa. In Madagascar they proceeded to build a society based on herding cattle and goats and pigs, farming, and fishing, and linked to the East African coast by Muslim traders.

  As interesting as Madagascar’s people are the wild animals that it has – and those that it lacks. Living in enormous abundance on the nearby African mainland are many species of large and conspicuous beasts that run on the ground and are active by day – the antelopes, ostriches, zebras, baboons, and lions that draw modern tourists to East Africa. None of these animals, and no animals remotely equivalent to them, have occurred on Madagascar in modern times. They were kept out by the 200 miles of sea separating Madagascar from Africa, just as the sea also kept Australia’s marsupials from reaching New Zealand. Instead, Madagascar supports two dozen species of small, monkey-like primates called lemurs, weighing only up to twenty pounds and mostly active at night and living in trees. Various species of rodents, bats, insectivores, and relatives of mongooses also occur, yet the largest still only weighs about twenty-five pounds.

  However, littering Madagascar’s beaches are proofs of vanished giant birds, in the form of countless eggshells of the size of a soccer ball. Eventually, bones turned up not only of the birds that laid those eggs, but also of a remarkable suite of vanished large mammals and reptiles. The egg-makers were half-a-dozen species of flightless birds up to 10 feet tall and weighing up to 1,000 pounds, like moas and ostriches but more massively built and hence now termed elephant birds. The reptiles were two species of giant land tortoises with shells about a yard long, and formerly very common, as indicated by the abundance of their bones. More diverse than either of these large birds or reptiles were a dozen species of lemurs up to the size of a gorilla, and all larger than or at least as large as the largest surviving lemur species. To judge from the small size of the eye orbits in their skulls, all or most of the extinct lemurs were probably diurnal rather than nocturnal. Some of them evidently lived on the ground like baboons, while others climbed in trees like orangutans and koala bears.

  As if all this were not enough, Madagascar also yielded the bones of an extinct ‘pygmy’ hippopotamus (‘only’ the size of a cow), an aardvark, and a big mongoose-related carnivore built like a short-legged puma. Taken together, these extinct large animals formerly gave Madagascar the functional equivalents of the surviving large beasts for which tourists still flock to African game parks – just as did New Zealand’s moas and other strange birds. The tortoises, elephant birds, and pygmy hippo would have been the herbivores replacing antelope and zebras; the lemurs would have replaced the baboons and great apes; and the mongoose-related carnivore made do for a leopard or scaled-down lion.

  What happened to all these big extinct mammals, reptiles, and birds? We can be confident that at least some of them were alive to delight the eyes of the first arriving Malagasy, who used elephant bird eggshells as water containers and discarded butchered bones of the pygmy hippo and some of the other species in their rubbish heaps. In addition, the bones of all the other extinct species are known from fossil sites only a few thousand years old. Since they must have evolved and survived for millions of years until then, it is unlikely that all those animals had the foresight to give up the ghost just in those last few moments before hungry humans showed up. In fact, a few may still have been holding out in remote parts of Madagascar when Europeans arrived, since the seventeenth-century French governor Flacourt was given descriptions of an animal suggestive of the gorilla-sized lemur. The elephant birds may have survived long enough to have become known to Arab traders in the Indian Ocean, and to have given rise to the account of the rok (a giant bird) in the tale of Sinbad the Sailor.

  Certainly some and probably all of Madagascar’s vanished giants were somehow exterminated by the activities of the early Malagasy. It is not hard to understand why the elephant birds became extinct, since their eggshells made such convenient two-gallon jerrycans. While the Malagasy were herders and fisherman rather than big-game hunters, the other big animals would have been easy prey, since they had never seen humans before. Probably, like New Zealand’s moas, they were as tame as Antarctic penguins
and other creatures that evolved in the absence of humans. A hungry Malagasy could have walked up to one of those tame beasts, clubbed it, and enjoyed a quick barbecue. That is presumably why the easy-to-see, easy-to-catch lemurs big enough to be worth the effort of butchering them – the large, diurnal, terrestrial species – all became extinct, while the small, nocturnal, tree-living ones all survived.

  However, unintended by-products of Malagasy activities probably killed more big animals than did hunting. Fires lit to clear forest for pasture and to stimulate growth of new grass each year would have destroyed habitats on which the beasts depended. Grazing cattle and goats also transformed habitats, as well as competing directly with grazing tortoises and elephant birds for food. Introduced dogs and pigs would have preyed on ground-dwelling animals, their young, and their eggs. By the time that the Portuguese arrived, Madagascar’s once-abundant elephant birds had all been reduced to eggshells covering the beaches, skeletons in the ground, and vague memories of roks.

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  Madagascar and Polynesia merely provide well-documented examples of the extinction waves that probably unfolded on all large oceanic islands colonized by people before the European expansion of the last 500 years. Like New Zealand and Madagascar, all such islands where life had evolved in the absence of humans used to have unique species of big animals that modern zoologists never saw alive. Mediterranean islands like Crete and Cyprus had pygmy hippos and giant tortoises (just as did Madagascar), as well as dwarf elephants and dwarf deer. The West Indies lost monkeys, ground sloths, a bear-sized rodent, and owls of several sizes: normal, giant, colossal, and titanic. It seems likely that these big birds, mammals, and tortoises too somehow succumbed to the first Mediterranean peoples or American Indians to reach their islands. Nor were birds the only victims. Mammals, lizards, frogs, snails, and even large insects disappeared as well, comprising thousands of species when one adds up all oceanic islands. Olson describes these insular extinctions as ‘one of the swiftest and most profound biological catastrophes in the history of the world’. However, we will not be sure that humans were responsible until the bones of the last animals and the remains of the first people have been dated more exactly for other islands, as has already been done for Polynesia and Madagascar.

  In addition to these pre-industrial extermination waves on islands, other species may have fallen victim to extermination waves on continents, in the more distant past. About 11,000 years ago, around the probable time that the first ancestors of American Indians reached the New World, most large species of mammals became extinct throughout all of North and South America. The disappearances involved species as varied as lions, horses, giant armadillos, mammoths, and saber-toothed cats. A long-standing debate has raged over whether these big mammals were done in by Indian hunters, or whether they just happened to succumb to climate changes around the same time. I shall explain in the next chapter why I personally think that hunters did it. However, it is much harder to pinpoint dates and causes of events that happened around 11,000 years ago than it is for recent events, like the collision of the Maoris and the moa within the past thousand years. Similarly, within the past 50,000 years Australia lost most of its big mammal species and was colonized by the ancestors of today’s Aboriginal Australians, but we are still uncertain whether the second event caused the first. Therefore, although it is now reasonably certain that the first pre-industrial peoples to reach islands wrought havoc among island species, the jury is still out on the question of whether this also happened on continents.

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  From all this evidence that the Golden Age was tarnished by exterminations of species, let’s now turn to evidence for destruction of habitats. Three dramatic examples involve famous archaeological puzzles: the giant stone statues of Easter Island, the abandoned pueblos of the American Southwest, and the ruins of Petra.

  An aura of mystery has clung to Easter Island ever since it and its Polynesian inhabitants were ‘discovered’ by the Dutch explorer Jakob Roggeveen in 1722. Lying in the Pacific Ocean 2,300 miles west of Chile, Easter surpasses even Henderson as one of the world’s most isolated scraps of land. Hundreds of statues, weighing up to eighty-five tons and up to 37 feet tall, were carved from volcanic quarries, somehow transported several miles, and raised to an upright position on platforms, by people without metal or wheels and with no power source other than human muscle. Even more statues remain unfinished in the quarries, or lie finished but abandoned between the quarries and platforms. The scene today is as if the carvers and movers had suddenly walked off the job, leaving an eerily silent landscape.

  When Roggeveen arrived, many statues were still standing, though new ones were no longer being carved. By 1840 all the erected statues had been deliberately toppled by the Easter Islanders themselves. How were such huge statues transported and erected, why were they eventually toppled, and why had carving ceased?

  The first of those questions was answered when living Easter Islanders showed Thor Heyerdahl how their ancestors had used logs as rollers to transport the statues and then as levers to erect them. The other questions were solved by subsequent archaeological and paleontological studies that revealed Easter’s gruesome history. When Polynesians settled Easter around 400 AD, the island was covered by forest that they gradually proceeded to clear, in order to plant gardens and to obtain logs for canoes and for erecting statues. By around 1500 AD the human population had built up to about 7,000 (over 150 per square mile), about a thousand statues had been carved, and at least 324 of those statues had been erected. But – the forest had been destroyed so thoroughly that not a single tree survived.

  An immediate result of this self-inflicted ecological disaster was that the islanders no longer had the logs needed to transport and erect statues, so that carving ceased. But deforestation also had two indirect consequences that brought starvation. These were soil erosion, causing lower crop yields, plus lack of timber to build canoes, resulting in less protein available from fishing. As a result, the population was now greater than Easter could support, and island society collapsed in a holocaust of internecine warfare and cannibalism. A warrior class took over; spear-points manufactured in huge quantities came to litter the landscape; the defeated were eaten or enslaved; rival clans pulled down each other’s statues; and people took to living in caves for self-protection. What had once been a lush island supporting one of the world’s most remarkable civilizations deteriorated into the Easter Island of today: a barren grassland littered with fallen statues, and supporting less than one-third of its former population.

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  Our second case study of pre-industrial habitat destruction involves the collapse of one of the most advanced Indian civilizations of North America. When Spanish explorers reached the US Southwest, they found gigantic multi-storey dwellings (pueblos) standing uninhabited in the middle of treeless desert. For example, the 650-room dwelling at Chaco Canyon National Monument in New Mexico was five stories high, 670 feet long, and 315 feet wide, making it the largest building ever erected in North America until topped by steel skyscrapers in the late Nineteenth Century. Navajo Indians in the region knew of the vanished builders only as ‘Anasazi’, meaning ‘the Ancient Ones’.

  Archaeologists subsequently established that construction of the Chaco pueblos began shortly after 900 AD, and that occupation ceased in the Twelfth Century. Why did the Anasazi erect a city in a barren wasteland, of all unpromising places? Where did they obtain their firewood, or the 16-foot-long wooden beams (200,000 of them!), that supported the roofs? Why did they then abandon the city that they had built at such enormous effort?

  The conventional view, analogous to the claim that Madagascar’s elephant birds and New Zealand’s moas died out from natural changes in climate, attributes the abandonment of Chaco Canyon to a drought. However, a different interpretation emerges from the work of paleobotanists Julio Betancourt, Thomas Van Devender, and their colleagues, who used an ingenious technique to decipher changes in Chaco vegetation
through time. Their method relied on the little rodents called packrats, which gather plants and other materials into shelters (‘middens’) that they eventually abandon after fifty or a hundred years but that remain well preserved under desert conditions. The plants can be identified centuries later, and the midden can be dated by radiocarbon techniques. Thus, each midden is virtually a time capsule of the local vegetation.

  By this method, Betancourt and Van Devender were able to reconstruct the following course of events. At the time that the Chaco pueblos were erected, they were not surrounded by barren desert but by pinyon and juniper woodland, with ponderosa pine forests nearby. This discovery at once solves the mystery of where the firewood and timber came from, and disposes of the apparent paradox of an advanced civilization rising from barren desert. As occupation continued at Chaco, however, the woodland and forest were cleared until the environment became the treeless wasteland that it remains today. The Indians were then having to go over ten miles to get firewood, and over twenty-five miles to get pine logs. When the pine forests had been felled, they built an elaborate road system to haul spruce and fir logs from mountain slopes over fifty miles away, relying on nothing more than their own muscle power. In addition, the Anasazi had solved the problems of agriculture in a dry environment by building irrigation systems to concentrate available water into valley bottoms. As deforestation caused progressively increasing erosion and water runoff, and as irrigation channels gradually dug gullies into the ground, the water table may finally have dropped below the level of the Anasazi fields, making irrigation without pumps impossible. Thus, while drought may have made some contribution to the Anasazi abandonment of Chaco Canyon, a self-inflicted ecological disaster was also a major factor.