LIVERPOOL, England, Sept. 21 (UPI) -- Climatic fluctuations drove key milestones in human evolution from the emergence of an early ancestor to the appearance of stone tools, British researchers say.
Scientists at the University of Liverpool reconstructed likely responses of human ancestors to the climate of the past 5 million years and found key evolutionary events coincided with periods of high variability in recorded temperatures, a university release said Wednesday.
Following the onset of high climatic variability around 2.7 million years ago a number of new species appear in the fossil record, researchers said.
"The first stone tools appear at around 2.6 million years ago, and doubtless assisted some of these species in responding to the rapidly changing climatic conditions," Liverpool researcher Matt Grove said. "The study confirmed that a major human adaptive radiation -- a pattern whereby the number of coexisting species increases rapidly before crashing again to near previous levels -- coincided with an extended period of climatic fluctuation."
However, he said, most of those species eventually disappeared.
"By 1.5 million years ago we are left with a single human ancestor -- Homo erectus. The key to the survival of Homo erectus appears to be its behavioral flexibility -- it is the most geographically widespread species of the period, and endures for over one and a half million years," Grove said.
"Homo erectus appears to have been a generalist, able to deal with many climatic and environmental contingencies."