This is the VOA Special English SCIENCE REPORT.
Scientists have long debated what caused many kinds of large animals in North America and Australia to disappear. Two new studies blame ancient humans for the disappearance. They say human hunters on both continents may have killed the animals for food. Science magazine reported the findings.
Thirteen-thousand years ago, North America was home to many large mammals. They included woolly mammoths, several kinds of horses, camels and oxen. However, these and many other animals died out soon after. More than seventy percent of the continent’s large mammals were affected.
John Alroy of the University of California at Santa Barbara led one of the studies. He developed a computer program to study the effect of human hunters on forty-one kinds of large mammals.
Mister Alroy based his study on evidence that humans first arrived in North America about thirteen-thousand years ago. He examined how a group of about one-hundred humans could grow in number over a period of one-thousand-two-hundred years. Mister Alroy estimated such things as reproduction rates and the amount of food humans need to survive. He found that it was possible for the small group of humans to expand to about three-hundred-thousand members during the period.
Mister Alroy said ancient humans could have killed off many kinds of large animals native to North America. He said the animals that disappeared had low rates of reproduction. This would have prevented them from recovering from the attacks by humans.
Science magazine also reported the findings of a study by Australian, French and American scientists. They studied fossil remains from twenty-eight areas across Australia and Papua New Guinea. The scientists said the fossils show that large animals in the area disappeared about forty-six-thousand years ago. That is a few thousand years after humans arrived.
More than thirty years ago, Paul Martin of the University of Arizona described how the disappearance of large animals was linked with human expansion. He says the two studies support his position. Mister Martin adds that local climate may have influenced the disappearance of some animals.
This VOA Special English SCIENCE REPORT was written by George Grow.