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JUNE 8, 2001

Research published in today's issue of Science provides a potentially controversial answer to a question that has been on the minds of scientists and Indian scholars alike.

Who -- or what -- killed off the big animals in the Americas?

Scientists have been debating the issue every since Paul Martin of the University of Arizona in the 1960s proposed his "overkill" theory. That is, humans eager for meat hunted the large animals, also known as megafauna, to death.

Not everyone has bought into the explanation, though. Climate change, disease, and alterations to habitat have been suggested as alternatives to over-hunting, since the phenomenon occurred elsewhere in the world, namely Australia.

And noted Indian author Vine DeLoria too has wondered how seemingly small groups of Indians could have caused the extinction of 73 percent of the large, plant-eating animals within 1,200 years of arriving in the Americas. These Indians must have been very busy, very productive, and very brave, he wrote in "Red Earth, White Lies," to attack animals that weighed as much as a ton while virtually ignoring more easily hunted species like bison, elk, and moose.

But according to John Alroy of the University of California, Santa Barbara, the answer to the debated question is indeed "who." As the author of a study on the extinction of large animals, he attributes the death of such species as woolly mammoths, camels, and the saber-toothed tiger to ancestors of today's American Indians.

In his study, Alroy considered two questions: whether the human population could have grown fast enough and whether humans could have hunted enough to drive the animals into extinction. He developed a computer simulation of human encroachment in an attempt to answer the questions.

The results of the simulation, not surprisingly, lead to his conclusion of human over-kill. Assuming a number of different scenarios of settlement and hunting, Alroy concludes that humans unleashed an "ecological catastrophe" on the animals without even knowing it.

"Human population growth and hunting almost invariably leads to a major mass extinction," he writes.

After the reported arrival of humans in the Americas about 13,000 years ago, almost all of the megafauna species died within 1,000 to 1,200 years. Alroy says his simulation correctly predicts the extinction or survival of 32 out of 41 species.

But Alroy also admits there are some problems that his simulation cannot resolve. As pointed out by others, elk, bison, and moose survived the Indian "invasion" unscathed.

At least when it comes to bison, Alroy has an explanation. Lower populations where bison were plentiful -- the northern Plains -- could have prevented their extinction, he suggests.

Two scientists from the American Museum of Natural History in New York City are criticizing Alroy's computer study as short-sighted. If humans did hunt these species to death, why did their activities stop about 10,000 years ago, questions Ross MacPhee. Alroy's model does not explain why or how these hunters apparently became eco-conscious, says MacPhee.

Yet MacPhee and fellow biologist Alex Greenwood don't let Indians off the hook. Instead, they say early humans introduced a "hyperdisease" which caused the animals to die out.

A companion study also published today looks at the extinction of megafauna in the Australias. Within 10,000 years of human arrival in Australia and West Papua New Guinea, 55 species went extinct.

In a written commentary, Leigh Dayton of Science writes that the studies -- if confirmed -- prove that "humans are guilty of two counts of serial mass murder, 35,000 years apart, and rival suspects such as climate change are off the hook."

Recommended Reading:
Red Earth, White Lies (Vine DeLoria 1997)

Relevant Links:
Science - http://www.sciencemag.org
Pleistocene Extinctions, the Death of an Ecosystem - http://www.well.com/user/elin/extinct.htm
Prehistoric Animals - http://dir.yahoo.com/Science/Earth_Sciences/Paleontology/
Prehistoric_Animals/Pleistocene_Megafauna/