ANTHROPOLOGICAL SCIENCE Vol. advpub, 000–000, 2007 Population history of the northern and central Nansei Islands (Ryukyu island arc) based on dental morphological variations: gene flow from North Kyushu to Nansei Islands Yoshitaka MANABE1*, Yoshikazu KITAGAWA1, Joichi OYAMADA1, Kazunari IGAWA1, Katsumoto KATO2, Naohiro KIKUCHI3, Hiromi MARUO3, Shigeru KOBAYASHI3, Atsushi ROKUTANDA1 1Department of Oral Anatomy and Dental Anthropology, Unit of Basic Medical Sciences, Course of Medical and Dental Sciences, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, 852-8588 Japan 2Department of Physical Therapy, Unit of Physical and Occupational Therapy, Course of Health Science, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, 852-8588 Japan 3Division of Anatomy, Kyushu Dental College, Kitakyushu, 803-8580 Japan Received 9 March 2007; accepted 20 July 2007 Abstract This study investigates dental morphological variations among the modern inhabitants of Tanegashima Island and Okinawa Main Island of the Nansei Islands (Ryukyu island arc), which is the southern gateway of the Japanese archipelago. Temporal variations within Tanegashima Island and re- gional variations of the northern half of the Nansei Islands were used to study population history. The late Aeneolithic Yayoi to protohistoric Kofun populations (c. 0–700 AD) of Tanegashima was found to be similar to the native Japanese populations, such as the Neolithic Jomonese (c. 10000–300 BC) and Hokkaido Ainu; however, the modern population of Tanegashima was similar to the migrant Jap- anese populations such as the post-Jomon people (c. 300 BC–present time) of the Japanese main is- lands. Using statistically sufficient materials, this study confirmed that a substantial change had oc- curred from the prehistoric to the modern period in Tanegashima Island. It is suggested that temporal change occurred in Tanegashima over approximately 1000 years after substantial change (c. 300 BC) in the Japanese main islands. The delay in temporal change in Tanegashima indicates that dispersal of migrant populations from northern Kyushu to its southern end occurred at a time remarkably later than the northeastward dispersal of migrant populations to central Honshu Island. Furthermore, the geo- graphical cline extending from North Kyushu to Okinawa Main Island via Tanegashima Island sug- gests southward gene flow from North Kyushu to the central Nansei Islands via the northeast end of the Nansei Islands. Key words: Nansei Islands, Ryukyu-Okinawa, Tanegashima, nonmetric dental traits, population history Introduction Main Island, from Pinza-Abu (c. 26000 BP) (Sakura, 1985) in Miyako Island, and from other sites in the Nansei Islands. The Nansei Islands, otherwise known as the Ryukyu is- Affinities between the Pleistocene humans of the Nansei Is- land arc, belong to Kagoshima and Okinawa prefectures and lands and the Jomonese (c. 12000–2300 BP) of the Japanese comprise a chain of Japanese islands situated in the western main islands can be perceived as one of the grounds support- Pacific Ocean at the eastern limit of the East China Sea. ing the southern origin theory regarding the Jomonese. In These islands extend southwest from Kyushu Island to Tai- addition, it is very important to investigate the southern dis- wan. It is of great importance to elucidate the physical an- persal of migrant populations from North to South Kyushu thropological characteristics on the Nansei Islands in order and the Nansei Islands from the viewpoint of dispersal of the to clarify the population history of the Japanese archipelago migrant populations that entered South Honshu and North and its peripheral regions, because these islands, which are Kyushu after the shift from the Jomon to the Yayoi period. located in the southern end of the Japanese archipelago, con- An investigation of the relationship between the Nansei stitute the southern gateway of gene flow to Japan. islanders (Ryukyu arc islanders) and other populations led to Some Pleistocene human fossil remains have been ex- the ‘Ainu–Ryukyuan common origin theory’. This theory is cavated from Minatogawa (c. 18000 BP) (Suzuki and K. one of the basic components of the now widely accepted Hanihara, 1982; Baba and Narasaki, 1991) in Okinawa ‘dual structure model’ for the population history of the Jap- anese by K. Hanihara (1991). Ever since a physical similari- * Corresponding author. e-mail: [email protected] ty between the Ryukyuan and Ainu populations was indicat- phone: +81-95-849-7626; fax: +81-95-849-7629 ed by von Baelz in 1911, many anthropological studies using Published online 14 November 2007 various methods have been conducted on Nansei islanders. in J-STAGE (www.jstage.jst.go.jp) DOI: 10.1537/ase.070309 The methods used in these studies comprised somatological © 2007 The Anthropological Society of Nippon 1 2 Y. MANABE ET AL. ANTHROPOLOGICAL SCIENCE measurements and observations (Newman and Eng, 1947; 2003a). Suda, 1950; Ikeda and Tagaya, 1980), osteological measure- In the present study, modern inhabitants of Okinawa Main ments and nonmetric traits (Hsu, 1948; Ikeda, 1974; Island, which is centrally located in the Nansei Islands, were Kohhara, 1976; Tagaya and Ikeda, 1976; Yamaguchi, 1982, investigated as a representative population of the Nansei Is- 1992; Mouri, 1986; Dodo, 1992; Pietrusewsky, 1994, 1997, lands. Furthermore, modern inhabitants of Tanegashima— 1999, 2004; Doi et al., 1997; Dodo et al., 1998, 2000; Doi, located at the entrance to the Nansei Islands from the south- 1998, 2003, 2004; Asato and Doi, 1999; Matsushita, 2001; ernmost Kyushu Island in the Japanese main islands—were Nakahashi, 2003), dental measurements and nonmetric studied to estimate the two-way genetic influence between traits (Yamada et al., 1970; K. Hanihara et al., 1974; K. Kyushu Island and the Nansei Islands. We investigated not Hanihara, 1976; Tsuru, 1978; Matayoshi, 1982; Turner, 1987; only the Ainu–Ryukyuan common origin theory based on T. Hanihara, 1989, 1991, 1992; Matsumura, 1995; Manabe the variations in the modern populations of Okinawa Main et al., 1999a, b, 2001, 2003a; Higa, 2003; Haneji, 2007), Island and Tanegashima Island but also the geographical and genetics (e.g. Omoto et al., 1976; Omoto, 1978, 1992; cline that indicates migratory direction. Horai et al., 1996; Omoto and Saitou, 1997; Hatta et al., The materials from the Aeneolithic Yayoi to the protohis- 1999; Tokunaga, 2003). However, the results that were toric Kofun period (0–700 AD) excavated from Tanegashi- obtained using these different methods and materials led to ma constitute a rare collection of materials in that they are diverse opinions, and there was no consensus with regard to available in statistically sufficient quantities among the pre- the anthropological positioning of the Nansei islanders in the historic human remains excavated from the Nansei Islands. Japanese archipelago and East Asia. These materials show dental characteristics that are similar In addition to the differences in the methods used, the lim- to those found in the Neolithic Jomonese (12000–2300 BP) itations involved in the different material gathering tech- of the Japanese main islands (Manabe et al., 2002). The ma- niques were also responsible for the lack of consensus. It is terials from the Yayoi–Kofun skeletal remains and from the crucial to collect data pertaining to each island in order to modern inhabitants of Tanegashima were compared using elucidate the regional variations in the arc-shaped Nansei Is- nonmetric dental traits in order to clarify the temporal lands, which spread over 1300 km, but difficult to collect changes that have occurred from the prehistoric to the mod- statistically sufficient data sets for each island from skeletal ern period in the area that forms the northern entrance to the remains. This is because, except for a few sites, the Nansei Nansei Islands. The period during which the temporal Islands do not yield an adequate amount of excavated skele- change occurred in Tanegashima was compared to the peri- tal materials for research purposes. However, tooth crown od when such changes occurred on the central Japanese morphology, for which samples can be gathered from the main island, with the aim to examine the possible causes that present inhabitants, can be used for collecting statistically underlie the regional differences in the timing of temporal sufficient data for each island. Moreover, to elucidate the changes. Finally, from the results of this study, as well as by population history of the Nansei Islands, it is as important to considering some recent osteological evidence (Doi et al., explain the temporal changes that occurred on each island as 1997; Doi, 1998, 2003, 2004; Dodo et al., 1998, 2000; Asato to reveal the regional variations. However, thus far, no study and Doi, 1999; Matsushita, 2001), we examine the charac- has inspected the temporal changes from the prehistoric to teristics of the prehistoric population of the Nansei Islands, the modern period on any of the Nansei Islands using statis- and discuss the validity of the ‘Jomonese–Ryukyuan com- tically sufficient data. mon origin theory’ from a prehistoric perspective. In order to inspect the temporal changes that have oc- curred from the past to the modern period, it is necessary to Materials and Methods conduct a simultaneous analysis of data from skeletal re- mains and present-day living persons. Tooth crown morpho- We investigated the modern inhabitants of Okinawa Main logical data enable this simultaneous analysis by using the Island (106 males/98 females), which constitutes the geo- same method of data collection for skeletons and living bod- graphical and political center of the Nansei Islands, and ies, while the simultaneous analysis of osteological and so- those of Tanegashima Island (68 males/61 females), which matometrical data is impossible. Nonmetric traits of tooth is located near the northern end of the Nansei Islands, at the crowns were considered in this study because variations in entrance to the Nansei Islands from Kyushu Island these traits in East Asia have been investigated in detail, and (Figure 1, Table 1).