Feb. 25, 2003 Archaeologists have uncovered another piece of evidence that seems to exonerate some of the earliest humans in North America of charges of exterminating 35 genera of Pleistocene epoch mammals.
The Clovis people, who roamed large portions of North America 10,800 to 11,500 years ago and left behind highly distinctive and deadly fluted spear points, have been implicated in the exterminations by some scientists.
Now researchers from the University of Washington and Southern Methodist University who examined evidence from all suggested Clovis-age killing sites conclude that there is no proof that people played a significant role in causing the extinction of Pleistocene mammals in the New World. Climate change, not humans, was the culprit.
"Of the 76 localities with asserted associations between people and now-extinct Pleistocene mammals, we found only 14 (12 for mammoth, two for mastodon) with secure evidence linking the two in a way suggestive of predation," write Donald Grayson of the UW and David Meltzer of SMU in the current issue of the Journal of World Prehistory. "This result provides little support for the assertion that big-game hunting was a significant element in Clovis-age subsistence strategies. This is not to say that such hunting never occurred: we have clear evidence that proboscideans (mammoths and mastodons) were taken by Clovis groups. It just did not occur very often."
To locate Clovis-age sites that suggested hunting of now-extinct mammals Grayson and Meltzer used FAUNMAP, an electronic database that documents the distribution of mammals in North America during the last 40,000 years. The search excluded areas above the North American ice sheet and sites that were pre- and post-Clovis because it is the Clovis people who have been targeted by proponents of the so-called "overkill" hypothesis.
This search turned up 75 locations in the United States and one in Canada that Grayson and Meltzer evaluated. Forty-seven of the sites did not exhibit minimally acceptable evidence showing an association between artifacts and extinct mammals. Most of these sites were rejected because they were not sufficiently described or documented.
"In many cases there is no published material, and when something is not published we are not able to weigh evidence of a human connection," said Grayson. "In other cases there was just an anecdotal suggestion of artifacts or remains, or there were very sketchy drawings."
Of the remaining 29 sites only 14 survived closer study. To determine this, the researchers looked for settings in which artifacts and animal remains were so closely associated that there was little doubt that their relationship was not accidental. In addition, Grayson and Meltzer searched published evidence for signs of human hunting and butchering and processing. This included cases where projectile points were found among bones or where there was solid evidence of human-caused bone breakage or cut marks.
Mammoth and mastodon bones were the most commonly found remains at the 14 confirmed predation sites, but horse, camel and bison bones also were identified. However, Grayson said there was no evidence that the two horse bones and one camel bone, all from extinct genera, came from animals that had been hunted by humans. There was quite a bit of evidence of human predation of bison, but this genus did not become extinct.
The survey produced no evidence that humans hunted the 33 other genera of extinct animals, which also include sloths, tapirs, bears and sabertooth cats. In fact, only 15 genera can be shown to have survived beyond 12,000 years ago and into Clovis times, said Grayson.
"There is absolutely no evidence that Clovis people were involved with 33 of the extinct genera. Where's the spear point sticking out of a camel or a ground sloth? If you can kill a mammoth you can kill a lumbering ground sloth. Clovis people absolutely did not chase these now-extinct animals relentlessly across the North American landscape," he said.
"The bottom line is that we need to stop wasting our time looking at people as the cause of these extinctions. We suspect the extinctions were driven by climate change. We need to know what aspects of climate change were involved. We have to tackle this species by species, one at a time, and look at the interaction of each species with the climate and vegetation on the ground."
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