25,000 years ago, during the Wurm glaciation, the climate of the northern hemisphere of Earth turned bitterly cold. Massive amounts of seawater turned to ice, dropping sea levels world wide. The conversion of sea water to ice exposed the floor of the Bering Sea that lies between Siberia and Alaska. 11,000 years later, hunter-gatherers living in northeast Asia followed the ice-age megafauna across the Bering Land Bridge into northwestern North America.
Physical anthropologists, studying the dental morphology of Native American populations, discovered that crown and root traits of those populations are shared by only one other group, Asians of northern Chinese descent. This similarity of dental features is called Sinodonty, (Chinese-like teeth). Further, geneticists found that a particular type of protein found in the blood serum of both North and South American Amerinds, called a Gm allotype, is also shared with northern Asians. Based on this finding, scientists calculated that the Amerind populations of the Americas seperated from the northern Chinese some 14,000 to 15,000 years ago.