The culture identified with the Japanese was not brought to the islands of Japan until about 300 B.C. It was brought by a people called the Yayoi from the Korean peninsula. It included rice cultivation and the use of steel for tools and weapons. There were aborigines in the islands at the time of the Yayoi migration. They had a hunting and gathering culture but they did make pottery and they are known by the name for the pottery, Jomon. The Jomon people were in the Japanese islands as far back as 30,000 B.C.

The people of Japan could derive genetically from either the Yayoi or the Jomon or a combination. Under one scenario the Yayoi largely replaced the Jomon. Under an alternate scenario the Yayoi brought the culture which was assimulated by the Jomon and the genes of the Yayoi are lost in the ocean of Jomon genes. In between these scenarios is the one in which the Japanese people are a mixture of the Yayoi and the Jomon. To the outside world the answer to which of these scenarios occurred is only mildly interesting, but to the Japanese themselves the answer is psychologically quite important.

At this point it must be noted that there has survived in Japan a people and culture of a hunting-and-gathering society called the Ainu. Whether the Ainu are the survivors of the Jomon people or not is a question still to be decided. Now the Ainu survive only on the northern island of Hokkaido but a few centuries ago they were an important element of the population of the main island of Honshu. The Ainu differ from the Japanese in that they have lighter skin and more body hairy. They were frequently referred to as the hairy Ainu.

To settle the question genetic researchers have been studying the presence of a particular gene on the Y-chromosome called the Y Alu polymorphic element (YAP). It developed in relatively recent history and so not all males have this gene. Michael Hammer at the University of Arizona at Tucson and Satoshi Horai of the National Institute of Genetics in Japan studied the occurrence of the YAP gene in populations in Asia. They found that the YAP gene does not occur among men from Korea or Taiwan. It occurs among Japanese men and then only with a special regional distribution. The YAP gene only occurs in Japan among the Ainu, the northern part of Japan and the southern part of Japan. In the central part of Japan the YAP gene does not occur. This suggests that the YAP gene developed among the Jomon and was passed on to the Yayoi only were there was racial mixing.

Hammer and Horai studied the distribution of another gene on the Y-chromosome. In this second case males in Korea possess this gene and it is more commonly found in the central part of Japan. The conclusion from the study is that there was a mixing of the Yayoi and Jomon in the extreme south (Okinawa) and the extreme north but none in the central area of Japan.

Masatoshi Nei of Pennsylvania State University investigated the occurrence of this other gene among males in Asia. He found a small occurrence among Mongolians but a 50 percent occurrence among Tibetan males. This suggests that the gene developed in north Asia and was carried by the ancestors of the Japanese and Koreans to the Korean peninsula and by the ancestors of the Tibetans from north Asia to the Tibetan plateau. This was perhaps the first evidence that the Tibetans were the descendants of migrants from north Asia.

The evidence appears to indicate that the Japanese are largely the descendants of the Yahoi with some mixture with the Jomon in the far north and the far south.