Asian human-origin theory gets new teeth.

Asian human-origin theory gets new teeth

An analysis of prehistoric and modern human teeth from around the world suggests anatomically modern humans arose in southeast Asia, not in Africa as a number of researchers have proposed.

The study indicates modern humans originated from only one geographically distinct population sometime between 50,000 and 100,000 years ago, says anthropologist Christy G. Turner II of Arizona State University in Tempe, who presented his data last week at the Circum-Pacific Prehistory Conference in Seattle. Since then, he contends, two large population clusters -- easily recognizable by their dental features -- have evolved. One cluster consists mainly of northeast Asians and residents of the Americas; the other encompasses Europeans, Africans, native Australians and southeast Asians. This "great web of humanity" apparently originated in southeast Asia, Turner says.

His findings contradict several studies of genetic material in modern populations, which indicate Europeans and Asians are linked together while Africans stand apart and probably formed the founding group of anatomically modern humans. The fossil record also holds suggestions that modern humans originated in Africa or the Middle East (SN: 2/27/88, p.138).

Turner's analysis of teeth in human populations involved more than 20 years of research. He based it on the measurement of "secondary traits," such as the number of bumps on the molar biting surface and the number of roots a tooth possesses. Primary traits, such as the number and types of teeth, remain stable across human populations. The frequencies of secondary traits provide a glimpse of population history and movement, Turner asserts, because they differ markedly between groups but are relatively stable over time within a group. They also remain largely unaffected by environmental factors such as climate, he says. In his view, secondary dental traits are most likely shaped by random genetic changes as small populations expand into new territories.

Turner's new study uses measurements of 28 secondary dental traits of more than 12,000 individuals from around the world. Most of the dental specimens come from archaeological collections, but Turner also included teeth from modern populations.

A statistical analysis and comparison of dental measurements for the 83 geographic populations in the sample shows that the southeast Asian dental pattern displays the least-specialized features of any group and provides the closest match of any single group to average dental measurements of all other world populations. Divergence from the average measurements of other populations increases with geographic distance from southeast Asia, Turner notes. If the evolution of secondary traits is largely influenced by random genetic change as colonies migrate to new areas, he theorizes, the region with the least divergence from other populations -- southeast Asia -- is where the colonists originated.

Turner says the dental data also suggest that most Native Americans are closely related to one another and originated in northeast Asia; Polynesians and Micronesians are more like southeast Asians than like native Australians and Melanesians; and native Australians most closely resemble Africans.

Dental analysis of population movements is still in its infancy, but Turner and two colleagues in an earlier study proposed the New World was probably settled by three waves of migrants from northeast Asia. Their analysis, described in the December 1986 CURRENT ANTHROPOLOGY, combined studies of variation in language, genetics and dental patterns, as well as archaeological finds. But the roots of east Asian populations prior to the appearance of modern humans remain unclear, Turner says.