February 5

Climate changes could have spelled demise of mammoths

New research focused on the Northeast, including Maine, challenges the notion that it was the arrival of hungry humans that led to the extinction of massive mammals.

By Michael Balter
Science

(Continued from page 1)

The new work bolsters the views of many researchers that “the arguments and evidence are stronger for environmental and climatic explanations,” says Lisa Nagaoka, a zooarchaeologist at the University of North Texas, Denton. By the time humans arrived, she says, the “tipping point” toward megafaunal extinctions may already have been reached.

And although these events occurred thousands of years ago, Lyman says that they have important implications today. Recently, a number of conservationists have begun advocating the “rewilding” of North America by reintroducing species such as elephants – which are closely related to extinct animals like mastodons and mammoths – and African lions, which are related to the extinct American lion.

This idea has received increasing attention in both the scientific literature and the popular media. For example, rewilding proponents advocate introducing elephants and Bactrian camels – which are now close to extinction in the Gobi Desert – onto the continent, with the idea that they would eat woody plants and weeds that threaten grasslands in the western United States, and that a new habitat would help protect them from extinction. But some researchers have argued that these proposals are based on faulty ecological logic and could end up hurting ecosystems rather than helping them, as well as threatening existing species.

And Lyman says that the strategy is based in large part on the ethical argument that because humans killed off relatives of these animals, they bear responsibility for now saving them and restoring their habitats. “The overkill hypothesis is a very weak foundation for rewilding.”

Meanwhile, advocates of the overkill hypothesis remain unconvinced by the new study. “The authors have engaged in an exercise in data analysis that neither proves nor disproves overkill,” says Gary Haynes, an archaeologist at the University of Nevada, Reno. Humans may have come into the northeast earlier than the radiocarbon database indicates, but their remains may not yet have been found, he says. Todd Surovell, an archaeologist at the University of Wyoming in Laramie, insists that the new study is entirely consistent with the view that humans dealt the final blow to the great beasts of North America: “The fundamental question is whether these animals would have suffered extinction if humans had not arrived.”

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