LONDON Climate change drove woolly mammoths to the edge of extinction and then humans finished them off, according to a Spanish study on Tuesday that adds to the debate over the demise of the Ice Age behemoths.
Using climate models and fossil remains, the researchers determined that warming temperatures had so shrunk the mammoths' habitat that when humans entered their territory about 6,000 years ago the species were already hanging by a thread.
"The collapse of the climatic niche of the mammoth caused a significant drop in their population size, making woolly mammoths more vulnerable to the increasing hunting pressure from human populations," the researchers wrote in the journal PLoS Biology.
There has been a spirited debate among scientists about what drove animals like the woolly mammoth into extinction, noted David Nogues-Bravo, a researcher at Museo Nacional Ciencias Naturales in Spain, who led the study.
Some argue that climate change was to blame while others promote the "blitzkrieg" or "overkill" theory proposed by University of Arizona scientist Paul Martin in 1967 that humans armed with primitive weapons devastated populations of animals that never previously had encountered people.
Untangling the two causes of extinction to determine which played the bigger role has proved tricky, with many studies looking to back one theory or the other, Nogues-Bravo said.
His team's approach was to compare a climate model with fossil remains collected from different points in time between 6,000 years ago and 126,000 years ago to analyze the individual role humans and the environment played.
This showed that warming climate had pushed the animals that thrived in cold dry tundra to the brink of extinction when humans pushed into their habitat mainly restricted to Arctic Siberia by 6,000 years ago.
The researchers estimated that based on the mammoth population at the time, humans would only have had to kill one animal each every three years to push the species to extinction.
"Our analyses suggest that the humans applied the coup de grace and that size of the suitable climatic area available in the mid-Holocene was too small to host populations able to withstand increased human hunting pressure," the researchers wrote.
(Reporting by Michael Kahn; Editing by Will Dunham)