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 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. 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
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.
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
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 paleo-botanists 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
