The Rise and Fall of the Third Chimpanzee

by Jared Diamond

  Chapter Eighteen looks more closely at the biggest, most dramatic, and most controversial of these ‘Golden Age mass extinctions’. Around 11,000 years ago most of the large mammals of two entire continents, North America and South America, became extinct. Around the same time appears the first unequivocal evidence for human occupation of the Americas, by the ancestors of American Indians. It was the biggest expansion of human territory since Homo erectus spread out of Africa to colonize Europe and Asia a million years ago. The temporal coincidence between the first Americans and the last big American mammals, the lack of mass extinctions elsewhere in the world at that same time, and proofs that some of the now-extinct beasts were hunted have suggested what is termed the New World blitzkrieg hypothesis. According to this interpretation, as the first wave of human hunters multiplied and spread from Canada to Patagonia, they encountered big animals that had never seen humans before, and they exterminated as they marched. However this theory’s critics are at least as numerous as its backers; Chapter Eighteen will try to make sense of the debate.

  The concluding chapter will seek to put approximate numbers on the count of species that we have already driven into extinction. We shall start with the firmest numbers: the species whose extinctions occurred in modern times and were well documented, and for which the search for survivors has been so thorough as to leave no doubt that there are no survivors. Next come estimates of three less certain numbers: the modern species that have not been seen alive for some time and that became extinct before anyone was aware of it; the modern species that have not even been ‘discovered’ and received a name; and the species that humans exterminated before the rise of modern science. That background will let us appraise the main mechanisms by which we exterminate, and the number of species that we are likely to exterminate within my sons’ lifetime – if we proceed at our current rate.

  SEVENTEEN

  THE GOLDEN AGE THAT NEVER WAS

  We cling to belief in a Rousseau-esque fantasy that the past was a Golden Age of environmentalism, when people lived in harmony with Nature. In reality, human societies, including those of stone-age farmers and possibly of hunter-gatherers as well, have been undermining their own subsistence by exterminating species and damaging environments for thousands of years. We differ from our supposedly conservationist forebears only in our greater numbers, more potent technology for inflicting damage, and access to written histories from which we refuse to learn.

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  Every part of the earth is sacred to my people. Every shining pine needle, every sandy shore, every mist in the dark woods, every clearing and humming insect is holy in the memory and experience of my people… . The white man … is a stranger who comes in the night and takes from the land whatever he needs. The earth is not his brother but his enemy… . Continue to contaminate your bed, and you will one night suffocate in your own waste. [From a letter written in 1855 to President Franklin Pierce, by Chief Seattle of the Duwanish tribe of American Indians.]

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  ENVIRONMENTALISTS SICKENED BY the damage that industrial societies are wreaking on the world often look to the past as a Golden Age. When Europeans began to settle America, the air and rivers were pure, the landscape green, the Great Plains teeming with bison. Today we breathe smog, worry about toxic chemicals in our drinking water, pave over the landscape, and rarely see any large wild animal. Worse is surely to come. By the time that my young sons reach retirement age, half of the world’s species will be extinct, the air radioactive, and the seas polluted with oil.

  Undoubtedly, two simple reasons go a long way towards explaining our worsening mess: modern technology has far more power to cause havoc than did the stone axes of the past, and far more people are alive now than ever before. But a third factor may also have contributed, a change in attitudes. Unlike modern city-dwellers, at least some pre-industrial peoples – like the Duwanish, whose chief I quoted – depend on and revere their local environment. Stories abound of how such peoples are in effect practising conservationists. As 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 are only beginning to realize how sophisticated are the conservationist policies of so-called ‘primitive’ peoples. For instance, well-intentioned foreign experts have made deserts out of large areas of Africa. In those same areas, local herders had thrived for uncounted millennia, by making annual nomadic migrations which ensured that land never became overgrazed.

  The nostalgic outlook shared until recently by most of my environmentalist colleagues and myself is part of a human tendency to view the past as a Golden Age in many other respects. A famous exponent of this outlook was the eighteenth-century French philosopher Jean–Jacques Rousseau, whose Discourse on the Origin of Inequality traced our degeneration from the Golden Age to the human misery that Rousseau saw around him. When eighteenth-century European explorers encountered pre-industrial peoples like Polynesians and American Indians, those peoples became idealized in European salons as ‘noble savages’ living in a continued Golden Age, untouched by such curses of civilization as religious intolerance, political tyranny, and social inequality.

  Even now, the days of classical Greece and Rome are widely considered to be the Golden Age of western civilization. Ironically, the Greeks and Romans also saw themselves as degenerates from a past Golden Age. I can still recite half-consciously those lines of the Roman poet Ovid that I memorized in tenth-grade Latin, ‘Aurea prima sata est aetas, quae vindice nullo …’ (‘First came the Golden Age, when men were honest and righteous of their own free will …’) Ovid went on to contrast those virtues with the rampant treachery and warfare of his own times. I have no doubt that any humans still alive in the radioactive soup of the Twenty-second Century will write equally nostalgically about our own era, which will then seem untroubled by comparison.

  Given this widespread belief in a Golden Age, some recent discoveries by archaeologists and paleontologists have come as a shock. It is now clear that pre-industrial societies have been exterminating species, destroying habitats, and undermining their own existence for thousands of years. Some of the best documented examples involve Polynesians and American Indians, the very peoples most often cited as exemplars of environmentalism. Needless to say, this revisionist view is hotly contested, not only in the halls of academia but also among lay people in Hawaii, New Zealand, and other areas with large Polynesian or Indian minorities. Are the new ‘discoveries’ just one more piece of racist pseudo-science by which white settlers seek to justify dispossessing indigenous peoples? How could the discoveries be reconciled with all the evidence for conservationist practices by modern pre-industrial peoples? If the discoveries were true, could we use them as case histories to help us predict the fate that our own environmental policies may bring upon us? Could the recent findings explain some otherwise mysterious collapses of ancient civilizations, like those of Easter Island or the Maya Indians?

  Before we can answer these controversial questions, we need to understand the new evidence belying the assumed past Golden Age of environmentalism. Let’s first consider evidence for past waves of exterminations, then evidence for past destruction of habitats.

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  When British colonists began to settle New Zealand in the 1800s, they found no native land mammals except bats. That was not surprising, for New Zealand is a remote island lying much too far from the continents for flightless mammals to reach. However, the colonists’ ploughs uncovered instead the bones and eggshells of large birds that were then already extinct but that the Maori (the earlier Polynesian settlers of New Zealand) remembered by the name moa. From complete skeletons, some of them evidently recent and still retaining skin and feathers, we have a good idea how moas must have looked alive: they were ostrich-like birds comprising a dozen species, and ranging from little ones ‘only’ 3 feet high and forty pounds in weight
up to giants of 500 pounds and 10 feet tall. Their food habits can be inferred from preserved gizzards containing twigs and leaves of dozens of plant species, showing them to have been herbivores. They thus used to be New Zealand’s equivalents of big mammalian herbivores like deer and antelope.

  While the moas are New Zealand’s most famous extinct birds, many others have been described from fossil bones, totalling at least twenty-eight species that disappeared before Europeans arrived. Quite a few besides the moas were big and flightless, including a big duck, a giant coot, and an enormous goose. These flightless birds were descended from normal birds that had flown to New Zealand and that had then evolved to lose their expensive wing muscles in a land free of mammalian predators. Others of the vanished birds, such as a pelican, a swan, a giant raven, and a colossal eagle, were perfectly capable of flight.

  Weighing up to thirty pounds, the eagle was by far the biggest and most powerful bird of prey in the world when it was alive. It dwarfed even the largest hawk now in existence, tropical America’s harpy eagle. The New Zealand eagle would have been the sole predator capable of attacking adult moas. Although some moas were nearly twenty times heavier than the eagle, it still could have killed them by taking advantage of the moas’ erect two-legged posture, crippling them with an attack on the long legs, then killing them with an attack on the head and long neck, and finally remaining for many days to consume the carcass, just as lions take their time at consuming a giraffe. The eagle’s habits may explain the many headless moa skeletons that have been found.

  Up to this point I have discussed New Zealand’s big extinct animals. But fossil-hunters have also discovered the bones of small scampering animals of the size of mice and rats. Scampering or crawling on the ground were at least three species of flightless or weak-flying songbirds, several frogs, giant snails, many giant cricket-like insects up to double the weight of a mouse, and strange mouse-like bats that rolled up their wings and ran. Some of these little animals were completely extinct by the time that Europeans arrived. Others still survived on small offshore islands near New Zealand, but their fossil bones show that they were formerly abundant on the New Zealand mainland. Collectively, all these now-extinct species that had evolved in isolation on New Zealand would have provided New Zealand with the ecological equivalents of the continents’ flightless mammals that had never arrived: moas instead of deer, flightless geese and coot instead of rabbits, big crickets and little songbirds and bats instead of mice, and colossal eagles instead of leopards.

  Fossils and biochemical evidence indicate that the moas’ ancestors had reached New Zealand millions of years ago. When and why, after surviving for so long, did the moas finally become extinct? What disaster could have struck so many species as different as crickets, eagles, ducks, and moas? Specifically, were all these strange creatures still alive when the ancestors of the Maoris arrived around 1000 AD?

  At the time that I first visited New Zealand in 1966, the received wisdom was that moas had died out because of a change in climate, and that any moa species surviving to greet the Maoris were on their figurative last legs. New Zealanders took it as dogma that Maoris were conservationists and did not exterminate the moas. There is still no doubt that Maoris, like other Polynesians, used stone tools, lived mainly by farming and fishing, and lacked the destructive power of modern industrial societies. At most, it was assumed, Maoris might have given the coup de grace to populations already on the verge of extinction. However, three sets of discoveries have demolished this conviction.

  Firstly, much of New Zealand was covered with glaciers or cold tundra during the last Ice Age ending about 10,000 years ago. Since then, the New Zealand climate has become much more favourable, with warmer temperatures and the spread of magnificent forests. The last moas died with their gizzards full of food, and enjoying the best climate that they had seen for tens of thousands of years.

  Secondly, radiocarbon-dated bird bones from dated Maori archaeological sites prove that all known moa species were still present in abundance when the first Maoris stepped ashore. So were the extinct goose, duck, swan, eagle, and other birds now known only from fossil bones. Within a few centuries, the moas and most of those other birds were extinct. It would have been an incredible coincidence if every individual of dozens of species that had occupied New Zealand for millions of years chose the precise geological moment of human arrival as the occasion to drop dead in synchrony.

  Finally, more than a hundred large archaeological sites are known – some of them covering dozens of acres – where Maoris cut up prodigious numbers of moas, cooked them in earth ovens, and discarded the remains. They ate the meat, used the skins for clothing, fashioned bones into fishhooks and jewellery, and blew out the eggs for use as water containers. During the Nineteenth Century moa bones were carted away from these sites by the wagonload. The number of moa skeletons in known Maori moa-hunter sites is estimated to be between 100,000 and 500,000, about ten times the number of moas likely to have been alive in New Zealand at any instant. Maoris must have been slaughtering moas for many generations.

  Hence it is now clear that Maoris exterminated moas, at least partly by killing them, partly by robbing their nests of eggs, and probably partly as well by clearing some of the forests in which moas lived. Anyone who has hiked in New Zealand’s rugged mountains will initially be incredulous at this thought. Just picture those travel posters of New Zealand’s fiordland, with its steep-walled gorges 10,000 feet deep, its 400 inches of annual rainfall, and its cold winters. Even today, full-time professional hunters armed with telescopic rifles and operating from helicopters cannot control the numbers of deer in those mountains. How could the few thousand Maoris living on New Zealand’s South Island and Stewart Island, armed only with stone axes and clubs and operating on foot, have hunted down the last moas?

  But there would have been a crucial difference between deer and moas. Deers have been selected for tens of thousands of generations to flee from human hunters, while moas had never seen humans until Maoris arrived. Like the naive animals of the Galapagos Islands today, moas were probably tame enough for a hunter to walk up to one and club it. Unlike deer, moas may have had such low reproductive rates that a few hunters visiting a valley only once every couple of years could kill moas faster than they could breed. That is precisely what is happening today to New Guinea’s largest surviving native mammal, a tree kangaroo in the remote Bewani Mountains. In areas settled by people, tree kangaroos are nocturnal, incredibly shy, live in trees, and are far harder to hunt than moas would have been. Despite all that, and despite the very low human population of the Bewanis, the cumulative effects of occasional hunting parties – literally one visit per valley per several years – have sufficed to bring this kangaroo to the verge of extinction. Having seen it happen to tree kangaroos, I now have no difficulty understanding how it happened to moas.

  Not only moas, but also all of New Zealand’s other extinct bird species, were still alive when Maoris landed. Most were gone a few centuries later. The larger ones – the swan and pelican, the flightless goose and coot – were surely hunted for food. The giant eagle, however, may have been killed by Maoris in self-defence. What do you think happened when that eagle, specialized at crippling and killing two-legged prey between three and ten feet tall, saw its first six-foot-tall Maoris? Even today, Manchurian eagles trained for hunting occasionally kill their human handlers, but the Manchurian birds were mere dwarfs beside New Zealand’s giant, which was pre-adapted to become a man-killer.

  Surely, though, neither self-defence nor hunting for food explains the rapid disappearance of New Zealand’s peculiar crickets, snails, wrens, and bats. Why were so many of those species exterminated, either throughout their range or else everywhere except on some offshore islands?

  Deforestation may be part of the answer, but the major reason was the other hunters that Maoris intentionally or accidentally brought with them – rats! Just as moas that evolved in the absence of humans were defenceless
against humans, so, too, small insular animals that evolved in the absence of rats were defenceless against rats. We know that the rat species spread by Europeans played a major role in modern exterminations of many bird species on Hawaii and other previously rat-free oceanic islands. For example, when rats finally reached Big South Cape Island off New Zealand in 1962, they exterminated or decimated the populations of eight bird species and a bat within three years. That is why so many New Zealand species are restricted today to rat-free islands, the sole places where they could survive when the tide of rats accompanying the Maoris swept over the New Zealand mainland.

  When the Maoris landed, they found an intact New Zealand biota of creatures so strange that we would dismiss them as science-fiction fantasies if we did not have their fossilized bones to convince us of their former existence. The scene was as close as we will ever get to what we might see if we could reach another fertile planet on which life had evolved. Within a short time, much of that community had collapsed in a biological holocaust, and some of the remaining community collapsed in a second holocaust following the arrival of Europeans. The end result is that New Zealand today has about half of the bird species that greeted the Maoris, and many of the survivors are either now at risk of extinction or else confined to islands with few introduced mammalian pests. A few centuries of hunting had sufficed to end millions of years of moa history.

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  Not only on New Zealand but on all other remote Pacific islands where archaeologists have looked recently in Polynesia, bones of many now-extinct bird species have been found at sites of the first settlers, proving there that the bird extinctions and human colonizations were somehow related. From all the main islands of Hawaii, paleontologists Storrs Olson and Helen James of the Smithsonian Institution have identified fossil bird species which disappeared during the Polynesian settlement that began around 500 AD. The fossils include not only small honey-creepers related to species still present but also bizarre flightless geese and ibises with no living close relatives at all. While Hawaii is notorious for its bird extinctions following European settlement, this earlier extinction wave had been unknown until Olson and James began publishing their discoveries in 1982. The known extinctions of Hawaiian birds before Captain Cook’s arrival now total the incredible number of at least fifty species, nearly one-tenth of the number of bird species breeding on mainland North America.