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The Japanese Roots (Part III)
Jared Diamond
11/9/2004

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JAPANESE CULTURE UNDERWENT FAR MORE RADICAL CHANGE in the 700 years of the Yayoi era than in the ten millennia of Jomon times. The contrast between Jomon stability (or conservatism) and radical Yayoi change is the most striking feature of Japanese history. Obviously, something momentous happened at 400 B.C. What was it? Were the ancestors of the modem Japanese the Jomon people, the Yayoi people, or a combination? Japan's population increased by an astonishing factor of 70 during Yayoi times: What caused that change? A passionate debate has raged around three alternative hypotheses.

One theory is that Jomon hunter-gatherers themselves gradually evolved into the modern Japanese. Because they had already been living a settled existence in villages for thousands of years, they may have been preadapted to accepting agriculture. At the Yayoi transition, perhaps nothing more happened than that jomon society received cold-resistant rice seeds and information about paddy irrigation from Korea, enabling it to produce more food and increase its numbers. This theory appeals to many modem Japanese because it minimizes the unwelcome contribution of Korean genes to the Japanese gene pool while portraying the Japanese people as uniquely Japanese for at least the past 12,000 years.

A second theory, unappealing to those Japanese who prefer the first theory, argues instead that the Yayoi transition represents a massive influx of immigrants from Korea, carrying Korean farming practices, culture, and genes. Kyushu would have seemed a paradise to Korean rice farmers, because it is warmer and swampier than Korea and hence a better place to grow rice. According to one estimate, Yayoi Japan received several million immigrants from Korea, utterly overwhelming the genetic contribution of Jomon people (thought to have numbered around 75,000 just before the Yayoi transition). If so, modern Japanese are descendants of Korean immigrants who developed a modified culture of their own over the last 2,000 years.

The last theory accepts the evidence for immigration from Korea but denies that it was massive. Instead, highly productive agriculture may have enabled a modest number of immigrant rice farmers to reproduce much faster than Jomon hunter-gatherers and eventually to outnumber them. Like the second theory, this theory considers modem Japanese to be slightly modified Koreans but dispenses with the need for large-scale immigration.

By comparison with similar transitions elsewhere in the world, the second or third theory seems to me more plausible than the first theory. Y, Over the last 12,000 years, agriculture arose at not more than nine places on Earth, including China and the Fertile Crescent. Twelve thousand years ago, everybody alive was a hunter-gatherer; now almost all of us are farmers or fed by farmers. Farming spread from those few sites of origin mainly because farmers outbred hunters, developed more potent technology, and then killed the hunters or drove them off lands suitable for agriculture. In modern times European farmers thereby replaced native Californian hunters, aboriginal Australians, and the San people of South Africa. Farmers who used stone tools similarly replaced hunters prehistorically throughout Europe, Southeast Asia, and Indonesia. Korean farmers of 400 B.C. would have enjoyed a much larger advantage over Jomon hunters because the Koreans already possessed iron tools and a highly developed form of intensive agriculture.

Which of the three theories is correct for Japan? The only direct way to answer this question is to compare Jomon and Yayoi skeletons and genes with those of modem Japanese and Ainu. Measurements have now been made of many skeletons. In addition, within the last three years molecular geneticists have begun to extract DNA from ancient human skeletons and compare the genes of Japan's ancient and modern populations. Jomon and Yayoi skeletons, researchers find, are on the average readily distinguishable. Jomon people tended to be shorter, with relatively longer forearms and lower legs, more wide-set eyes, shorter and wider faces, and much more pronounced facial topography, with strikingly raised browridges, noses, and nose bridges. Yayoi people averaged an inch or two taller, with close-set eyes, high and narrow faces, and flat browridges and noses. Some skeletons of the Yayoi period were still Jomon-like in appearance, but that is to be expected by almost any theory of the Jomon-Yayoi transition. By the time of the kofun period, all Japanese skeletons except those of the Ainu form a homogeneous group, resembling modern Japanese and Koreans.

In all these respects, Jomon skulls differ from those of modern Japanese and are most similar to those of modern Ainu, while Yayoi skulls most resemble those of modern Japanese. Similarly, geneticists attempting to calculate the relative contributions of Korean-like Yayoi genes and Ainu-like Jomon genes to the modem Japanese gene pool have concluded that the Yayoi contribution was generally dominant. Thus, immigrants from Korea really did make a big contribution to the modern Japanese, though we cannot yet say whether that was because of massive immigration or else modest immigration amplified by a high rate of population increase. Genetic studies of the past three years have also at last resolved the controversy about the origins of the Ainu: they are the descendants of Japan's ancient Jomon inhabitants, mixed with Korean genes of Yayoi colonists and of the modern Japanese.

Given the overwhelming advantage that rice agriculture gave Korean farmers, one has to wonder why the farmers achieved victory over Jomon hunters so suddenly, after making little headway in Japan for thousands of years. What finally tipped the balance and triggered the Yayoi transition was probably a combination of four developments: the farmers began raising rice in irrigated fields instead of in less productive dry fields; they developed rice strains that would grow well in a cool climate; their population expanded in Korea, putting pressure on Koreans to emigrate; and they invented iron tools that allowed them to mass-produce the wooden shovels, hoes, and other tools needed for rice-paddy agriculture. That iron and intensive farming reached Japan simultaneously is unlikely to have been a coincidence.

Source: Discover, June 1998 Vol. 19

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