ＤＮＡ解析が解明する現生人類の起源と拡散

Abstract

Modern DNA—maternally inherited mitochondrial DNA and paternally inherited Y-chromosomal DNA in particular—is now routinely used to trace ancient human routes. It appears that genetic data can actually offer a means of better understanding ancient population movements. The DNA patterns of present-day world populations indicate that modern humans emerged from Africa at least 150,000 years ago. These populations dispersed from Africa to most other parts of the world at least 60,000 years ago along the tropical coasts of the Indian Ocean to Southeast Asia and Australasia. Genetic data support a model for the peopling of the New World in which Native American ancestors diverged from the Asian gene pool and experienced a gradual population expansion as they moved into Beringia. After a long period in greater Beringia, these ancestors rapidly spread into the Americas at least 15,000 years ago. Examinations of ancient human bones using molecular genetic techniques provide direct access to genetic information on past populations. The retrieval and analysis of ancient DNA is more difficult than that of modern DNA. However, this technique holds great potential for inferring the origins of the Japanese people. The distribution of mitochondrial DNA haplogroups among the Jomon, Yayoi, and modern Japanese populations suggests that the formation of the Japanese population was not the result of a population expansion. Distinctively different frequencies of mitochondrial DNA haplogroups among Jomon and Yayoi populations indicate significantly different population histories for these groups. However, both populations have contributed to the formation of the modern Japanese population. An eastward population expansion from the Asian Continent during the Yayoi period resulted in the admixture of these people with the indigenous Jomon people and led to the formation of the basic pattern seen in modern Japanese people.