Key to Martin’s Blitzkrieg theory is that in at least 14 of those sites, Clovis points were found with mammoth or mastodon skeletons, some stuck between their ribs. “If
All these existed, the fossil record shows, but not everyone agrees on what happened to them. One challenge to Paul Martin’s theory questions whether Clovis people were actually the first humans to enter the New World. Among the objectors are Native Americans wary of any suggestion that they immigrated, which would undermine their indigenous status; they denounce the idea that their origins trace to a Bering land bridge as an attack on their faith. Even some archaeologists question whether a Bering ice-free corridor really existed, and suggest that the first Americans actually arrived by water, skirting the ice sheet to continue down the Pacific coast. If boats reached Australia from Asia nearly 40 millennia earlier, why not boats between Asia and America?
Still others point to a handful of archaeological sites that supposedly predate Clovis. Archaeologists who excavated the most famous of these, Monte Verde, in southern Chile, believe that humans may have settled there twice: once 1,000 years prior to Clovis, the other time 30,000 years ago. If so, at that time the Bering Strait would likely not have been dry land, meaning an ocean voyage from some direction was involved. Even the Atlantic has been suggested, by archaeologists who think that Clovis techniques for flaking chert resemble paleolithics that developed in France and Spain 10,000 years earlier.
Questions about the validity of Monte Verde’s radiocarbon dates soon cast doubt over initial claims that it proved early human presence in the Americas. Matters were further muddied when most of the peat bog that had preserved Monte Verde’s poles, stakes, spear points, and knotted grasses was bulldozed before other archaeologists could examine the excavation site.
Even if early humans did somehow find their way to Chile before Clovis, argues Paul Martin, their impact was brief, local, and ecologically negligible, like that of the Vikings who colonized Newfoundland before Columbus. “Where are the abundant tools, artifacts, and cave paintings that their contemporaries left all over Europe? Pre- Clovis Americans wouldn’t have met competing human cultures, like the Vikings did. Only animals. So why didn’t they spread?”
The second, more fundamental controversy about Martin’s Blitzkrieg theory, for years the most accepted explanation for the fate the of the New World’s big animals, asks how a few nomadic bands of hunter-gatherers could annihilate tens of millions of large animals. Fourteen kill sites on an entire continent hardly add up to megafaunal genocide.
Nearly half a century later, the debate Paul Martin ignited remains one of science’s greatest flash points. Careers have been built upon proving or attacking his conclusions, fueling a protracted, not-always-polite war waged by archaeologists, geologists, paleontologists, dendro- and radiochronologists, paleoecologists, and biologists. Nevertheless, nearly all are Martin’s friends, and many are his former students.
The leading alternatives they’ve proposed to his overkill theory involve either climate change or disease, and have inevitably come to be known as “over-chill” and “over-ill.” Over-chill, with the greatest number of adherents, is partly a misnomer, because both overheating and overcooling get blamed. In one argument, a sudden temperature reversal at the end of the Pleistocene, just as glaciers were melting away, plunged the world briefly back into the Ice Age and caught millions of vulnerable animals unaware. Others propose the opposite: that rising Holocene temperatures doomed furry species, because they had adapted over thousands of years to frigid conditions.
Over-ill suggests that arriving humans, or creatures that accompanied them, introduced pathogens that nothing alive in the Americas had ever encountered. It may be possible to prove this by analyzing mammoth tissues that will likely be discovered as glaciers continue to thaw. The premise has a grim analog: Most descendants of whoever were the first Americans died horribly in the century following European contact. Only a tiny fraction lost their lives to the point of a Spanish sword; the rest succumbed to Old World germs for which they had no antibodies: smallpox, measles, typhoid, and whooping cough. In Mexico alone, where an estimated 25 million Meso-Americans lived when the Spaniards first appeared, only 1 million remained 100 years later.
Even if disease mutated from humans to mammoths and the other Pleistocene giants, or passed directly from their dogs or livestock, that would still put the blame on
Ancient European sites show that
Plants, even less mobile than animals, and generally more climatesensitive, also seem to have survived. Among the sloth dung in Rampart and other Grand Canyon caves, Martin and his colleagues encountered ancient pack rat middens layered with thousands of years of vegetation remains. With the possible exception of a single variety of spruce, no species harvested by pack rat or sloth residents of these caves met temperatures extreme enough to spell their extinction.
But the clincher for Martin is the sloths. Within a millennium of the Clovis people’s appearance, every slow, plodding, easy target of a ground sloth was gone—on the continents of North and South America. Yet radiocarbon dates confirm that bones found in caves in Cuba, Haiti, and Puerto Rico belonged to ground sloths still alive 5,000 years later. Their ultimate disappearance coincided with the eventual arrival of humans in the Greater Antilles 8,000 years ago. In the Lesser Antilles, on islands that humans reached even later, like Grenada, the sloth remains are even younger.
“If a change in climate was powerful enough to exterminate ground sloths from Alaska to Patagonia, you’d expect it would also take them out in the West Indies. But that didn’t happen.” This evidence also suggests that the first Americans arrived on the continent on foot, not as seafarers, since it took them five millennia to reach the Caribbean.
On another, far-distant island, is a further hint that, had humans never evolved, Pleistocene megafauna might be around today. During the Ice Age, Wrangel Island, a wedge of rocky tundra in the Arctic Ocean, was connected to Siberia. It was so far north, however, that humans entering Alaska missed it. As warming seas rose in the Holocene, Wrangel was again isolated from the mainland; its population of woolly mammoths, spared but now stranded, was forced to adapt to the limited resources of an island. During the span in which humans went from caves to building great civilizations in Sumer and Peru, Wrangel Island’s mammoths lived on, a dwarf species that lasted 7,000 years longer than mammoths on any continent. They were still alive 4,000 years ago, when Egyptian pharaohs ruled.
More recent still was the extinction of one of the most astonishing of Pleistocene megafauna: the world’s biggest bird, which also lived on an island humans overlooked. New Zealand’s flightless moa, at 600 pounds, weighed twice as much an ostrich and stood nearly a yard taller. The first humans colonized New Zealand about two centuries before Columbus sailed to America. By the time he did, the last of 11 moa species was all but gone.
To Paul Martin, it’s obvious. “Big animals were the easiest to track. Killing them gave humans the most food, and the most prestige.” Within 100 miles of his Tumamoc Hill laboratory, past the Tucson jumble, are three of the 14 known Clovis kill sites. The richest of them, Murray Springs, strewn with Clovis spear points and dead mammoths, was found by two of Martin’s students, Vance Haynes and Peter Mehringer. Its eroded strata, wrote Haynes, resembled “pages in a book that record the last 50,000 years of Earth history.” Those pages contain
