Prehistory and Quaternary Research are comprehensive, interdisciplinary sciences that study specific time periods. It is extremely important for prehistory to cooperate with Quaternary research because one of its major tasks is to understand the ancient environment that served as the stage for human lives. On the other hand, the Quaternary period, formerly called the Anthropogene, today basically refers to the same period of time as when the Homo genus evolved. An increasing number of animal and plant remains are being excavated at archaeological sites from the Holocene, and environmental archaeology research on this period, which actively uses the analyses of various natural sciences while aiming to elucidate human activities and the ancient environment that served as their stage, is flourishing. On the other hand, it is also necessary to make clear the influence upon human activities of environmental events. When doing so, first it is necessary to examine the temporal relationship between human activities and environmental events. Chronology, connecting them, plays a major role in this.

This paper compiles archaeobotanical size data of soybean, azuki, and Echinochloa (barnyard grass) and discusses the process of morphological domestication (seed enlargement) of these three plants during the Jomon period. The archaeobotanical records of soybean and azuki increased from 6000 to 4000 years ago in the Chubu and western Kanto regions (Moroiso-Katsusaka Pottery grope), and the records include seeds larger than modern wild species. This trend was linked with the population growth in this region, and morphological domestication probably started from this period. However, small seeds have also been seen in this stage ; gathering of wild species by the people probably still continued, or large seed species were not fixed. Large seed species disappeared in the Chubu region 4000 years ago ; however, the large seeds can be seen in Kyushu and western Japan. Probably the large seed species were fixed from this stage, and cultivation of these large species at least had started in this period. In the case of Echinochloa (barnyard grass), the seed size temporally enlarged 6000 years ago in the northern Tohoku, and 4500 years ago in the southern Hokkaido region (Ento pottery group). This seed enlargement was also linked with population growth in each period and region. There are some possibilities that morphological domestication temporally occurred in these periods ; however, large seeds were not seen until the 10th century. Since the small seeds of Echinochloa were not seen after the 10^th century, it seems that the large seed species have been fixed since this period.