Humans in eastern Asia show ancient roots.

A new analysis of stone tools in northeastern China's Nihewan Basin indicates that human ancestors lived there about 1.36 million years ago, making it the oldest confirmed occupation site in eastern Asia.

Homo erectus groups that entered northeastern Asia from more southerly locales learned to handle the region's intermittent periods of drought and intense cold that characterized the Stone Age, concludes a team led by geologist Rixiang X. Zhu of the Chinese Academy of Sciences in Beijing. Zhu and his colleagues describe their findings in the Sept. 27 NATURE.

"The spread of stone-tool makers to northern China implies that early human populations in eastern Asia were able to adapt to diverse climatic settings," says anthropologist and study coauthor Richard Potts of the Smithsonian Institution in Washington, D.C.

Potts theorizes that global fluctuations in climate and landscape favored the evolution of animals adept at surviving in shifting environments (SN: 7/12/97, p. 26).

The new results derive from an analysis of ancient polar reversals--in which the planet's south and north poles exchange magnetic traits. The magnetic orientations of minerals at two northeastern Chinese sites reflect such reversals. One of these sites, Xiaochangliang, had previously yielded more than 3,000 stone artifacts.

The researchers view their age estimate with confidence, since the sites contain nearly identical soil-layer sequences as well as corresponding signatures of the same polar reversals. Sediment bearing stone tools was deposited between the polar reversals that occurred 1.77 million and 1.07 million years ago. The artifacts' position in the layers enabled the scientists to zero in on a final age estimate of 1.36 million years.

Climatic changes spurred population movements of either H. erectus or Homo ergaster from western to eastern Asia, Potts theorizes (SN: 5/13/00, p. 308). An H. erectus site at Lantian, about 560 miles southwest of Xiaochangliang, had already been dated to 1.15 million years ago.

Zhu's team provides solid evidence for the oldest known human occupation in eastern Asia, comments anthropologist F. Clark Howell of the University of California, Berkeley. "Penetration into eastern Asia occurred substantially earlier than anything we know about in Europe," Howell says.