Related Work

Nakahashi and Iizuka (1998, 2008) have provided insights into the initial size of the immigrant population and which group played a formative role in establishing Yayoi agrarian culture, based on their discriminant analysis of human bone material.

They have indicated that people bearing similar traits to those of the immigrants accounted for approximately 80 % of the total population during the middle Yayoi period. Furthermore, they applied a mathematical equation model to propose features of ancient population dynamics up to the middle of the Yayoi period. Considering the differences in the population growth rates of the native Jomon people (0.1 % per annum) and immigrants (1.3 % per annum), they suggested that even a small number of immigrants could account for the large majority that prevailed a few hundred years later. That is, in contrast to conventional studies, these studies have demonstrated the possibility that even a small initial immigrant population could explain why anthropological investigations of the morphology of human bones have revealed differences during the Yayoi and Jomon periods. Kataoka and Iizuka (2006) have also estimated the population growth rate based on the inhabitants of excavated houses, determined by house plans, site locations, and settlement composition. They have suggested that only immigrants could account for the large majority that prevailed a few hundred years later. Therefore, only the immigrants could have played a key role in establishing the Yayoi agrarian culture.

These studies (Nakahashi and Iizuka 1998, 2008; Kataoka and Iizuka 2006) are remarkable in that they have adopted a quantitative approach, using mathematical models, to present objective results. However, a few unresolved issues remain. First, these studies are premised on a model that partially segregates native Jomon people and immigrants.

Even assuming the composition of a mixed group of Jomon people and immigrants, a small sized mixed group population has been estimated with a low ratio of native Jomon people within the group. This assumption would be unreasonable if there was no barrier prohibiting marriage and inter-group contact, and if mating was possible between Jomon people and immigrants. That is, the effects of random mating between these groups have been ignored. Second, these studies have assumed that genetic traits and the food production system were not separated. Therefore, they did not consider the diffusion of the food production system. The fertility rate of a population depends on its food production system (Bentley et al. 1993). Thus, it is possible that the population growth rate also depended on a subsistence culture. These studies are, therefore, unable to address the fundamental question of who played a formative role in the establishment of the agrarian culture.

Additionally, the immigrant sex ratio remains an important unresolved factor. As previously mentioned, one leading hypothesis postulates that the immigrants were primarily male (Kaneseki 1976), based on the assumption that pottery and stone tools were primarily produced by females (Tsude 1982), and on the evident characteristics of pottery and stone tools that retained the Jomon style at the onset of the Yayoi period. This implies that, if native Jomon females produced pottery, then male immigrants mated with native Jomon females. Nakahashi and lizuka (1998, 2008) have calculated that the majority of females in the mixed group population comprising native Jomon people and immigrants were Jomon females. However, these studies originally assumed the existence of a small mixed group. Thus, they were unable to estimate the sex ratio of the totality of immigrants. Furthermore, this hypothesis is inconsistent with studies that show that the haplotype frequency of the maternal mitochondrial DNA (mtDNA) of Jomon people differs significantly from that of people of the Yayoi period because of the genetic influence of Chinese-Koreans (Shinoda 2006).

We, therefore, posit that the low ratio of immigrant females made it difficult to change the frequency of mtDNA between Jomon people and people of the Yayoi period. That is, at the beginning of the Yayoi period, the argument that pottery and stone tools retained the characteristics of Jomon style is inconsistent with the significant changes that occurred in the haplotype frequency of mtDNA between populations of the Jomon and Yayoi periods. Therefore, the problem of the immigrant sex ratio cannot be resolved through the application of a conventional static model.

In this study, we propose an alternative view of Japanese history using agent-based modeling techniques instead of using the mathematical model developed by Nakahashi and Iizuka (1998, 2008). In formulating this model, based on the reviewed literature, we assumed the following four points: (1) A large number of native Jomon people and a small number of Chinese-Korean immigrants coexisted in the Northern Kyushu region. (2) During the 300 years that followed immigration, people bearing immigrant traits accounted for 80 % of the total population. (3) The model incorporates both random mating and random diffusion of the agrarian culture. (4) We further examined the immigrant sex ratio by adding the pottery style and mtDNA inheritance. We used these assumptions and agent-based simulation (ABS) to examine the issue of who played a formative role in establishing Yayoi agrarian culture.

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Source: Barcelo Juan A., Del Castillo Florencia (eds.). Simulating Prehistoric and Ancient Worlds. Springer,2016. — 410 p.. 2016

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