Magazine article Science News

Jomon Genes: Using DNA, Researchers Probe the Genetic Origins of Modern Japanese

Magazine article Science News

Jomon Genes: Using DNA, Researchers Probe the Genetic Origins of Modern Japanese

Article excerpt

Japan is generally considered one of the most modern, forward-looking countries in the world. Yet the Japanese also have an intense fascination with their islands' past, particularly the history and continuing influence of two peoples known as the Jomon and the Yayoi.

The Jomon, the original inhabitants of Japan, are thought to have migrated from the Asian mainland at a time when the two regions were physically connected. When sea levels began to rise about 12,000 years ago, the Japanese archipelago became separate from continental Asia, and the Jomon were left to spread across the islands. Hunters, fishers, and foragers, the Jomon were also the world's first known potters. Indeed, their name-Japanese for cord marks-stems from the ropelike impressions found in their clay pottery.

Scholars agree that the Jomon period of Japan's history ran from at least 10,000 years ago to about 250 B.C. At that point, the Yayoi, apparently traveling in ships from the Korean peninsula, arrived at the islands. The Yayoi culture, marked by weaving, metalworking, and, most important, the farming of rice, soon supplanted that of the Jomon.

During the last century, anthropologists have fiercely debated whether the Jomon or the Yayoi were the true ancestors of the modern Japanese. For most of this debate's history, scientists have addressed the issue by comparing Asian languages, analyzing archaeological ruins, and measuring dental or other skeletal remains.

Over the last few years, another kind of evidence has begun to have an impact on the debate. By studying the genes of modern Japanese and of other Asians, and even the ancient DNA in the fossilized bones of the Jomon and the Yayoi, investigators hope to put together a genetic history of Japan. Researchers have recently examined, for example, the Y chromosomes of people throughout Asia.

In conjunction with other historical evidence, the new work suggests that the Jomon did not originate in Southeast Asia, as one long-standing theory has it, but farther north. The research also sheds light on the extent to which the Jomon and the Yayoi have influenced the genetic makeup of modern Japanese.

"Our data clearly show that both Yayoi and Jomon genes have made a contribution to the contemporary gene pool," says Michael F. Hammer, who presented the Y chromosome research in October 1996 at the American Society of Human Genetics meeting in San Francisco.

Three theories have dominated the debate about the origin of the modern Japanese people. The replacement theory argues that the invading Yayoi wiped out the Jomon both culturally and genetically. Proponents of this option contend that the only remaining descendants of the Jomon are the Ainu in Hokkaido, the northernmost of the Japanese islands, and some inhabitants of Japan's southernmost islands. Among the physical features that make the Ainu distinct from most Japanese are lighter skin and more body hair.

"The Jomon are the obvious ancestors of the Ainu but not of modern Japanese," says C. Loring Brace, an anthropologist at the University in Michigan in Ann Arbor.

The transformation hypothesis holds that the Yayoi culture did supplant the Jomon culture but that the Yayoi did not come to Japan in large enough numbers to influence significantly the Jomon gene pool.

"Genetically, there's not much difference between the Jomon people and the current Japanese," asserts Masatoshi Nei, a population geneticist at Pennsylvania State University in State College and one of the strongest supporters of the transformation model.

The final theory offers a compromise. Usually referred to as the hybridization, or dual structure, model, it suggests that both the Yayoi and the Jomon have contributed significantly to the genes of most living Japanese.

Hammer, a researcher at the University of Arizona in Tucson, and Satoshi Horai, who works at the National Institute of Genetics in Mishima, Japan, addressed these theories with their study of the Y chromosome. …

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