MOSCOW, RUSSIA—Paleontologist Pavel Nikolskiy and archaeologist Vladimir Pitulko of the Russian Academy of Sciences think that people who lived in Siberia between 33,500 and 31,500 years ago hunted mammoths every few years, when they needed their ivory tusks for tool making. The bones of at least 31 mammoths that had been hunted over a period of 2,000 years have been uncovered at the Yana archaeological site. Stone spear points found in some of the bones suggest that hunters attacked their large prey from behind.