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...structure present-day Rapanui and how has evolved, we must consider its history, geographic isolation, and, above all, the events that have had important demographic consequences.
Archeological evidence indicates that initial settlement of the island was by Polynesians, who had previously colonized Fiji, Tonga, and Samoa in the central South Pacific. Various studies have attempted to determine the date of these first settlers on Rapanui. Smith (1961) obtained a radiocarbon date of A.D. 400, but subsequent radiocarbon dating of sites on the island strongly suggests that settlement before A.D. 800 was unlikely (Martinsson-Wallin and Crockford 2002). More recently, Hunt and Lipo (2006), on the basis of radiocarbon analysis of stratigraphic layers at Anakena, concluded that the island was colonized about A.D. 1200. This recent date fits well with evidence of colonization elsewhere in the southeastern Pacific (Spriggs and Anderson 1993; Anderson and Sinoto 2002; Wilmshurst and Higham 2004).
The origin of the first settlers on Rapanui has been studied using molecular genetic approaches (Hill and Serjeantson 1989; Hagelberg and Clegg 1993; Hagelberg et al. 1994; Lum et al. 1994; Redd et al. 1995). Some investigators hypothesize that there was a single migration event (Bahn and Flenley 1992; Drusini 1994), whereas others suggest that there were waves of migration (Metraux 1941, 1957; Heyerdahl and Ferdon 1961; Englert and Cruz-Coke 1981). A more complex settlement model for the Pacific has also been proposed, with some investigators suggesting that exploration was rapid, purposeful, and systematically undertaken (Irwin 1992; Matisoo-Smith et al. 1998). The material culture, monumental architecture, language, and customs of Rapanui suggest that the original settlers came from either the Marquesas or the Mangareva Islands (Martinsson-Wallin and Crockford 2002). Admixture of the native Rapanui population with Amerindians at the time of initial settlement has been suggested by Heyerdahl (1958) and also hypothesized by Gill et al. (1997) on the basis of cranial morphology.
Hurles et al. (2003) suggested that native American Y chromosomes were introduced to the island before the 20th century, most likely from five members of a Peruvian slave ship that arrived on the island immediately before the population crash of 1864, after which only 20 adult males are thought to have survived (Green 2000). The crew's genetic contribution may have been amplified in subsequent generations because of their greater resistance to an epidemic of either dysentery or smallpox that devastated the Polynesian population.
The size of the Rapanui population has always been determined by ecological and historical events. Easter Islanders reached their zenith, of about 10,000 individuals, in the 17th century, and this number exceeded the island's carrying capacity (Hernandez et al. 2000). Consequently, resources became scarce and the once lush palm forests were destroyed. Hernandez et al. (2000) suggested that overpopulation was the cause of island deforestation and the social conflict that led to a period of decadence, destruction of the statues, and a massive population decrease.
In 1862-1863 pirates enslaved a large number of Rapanui inhabitants to collect guano on the coast of Peru. Some survivors were repatriated in 1864, but they brought with them diseases such as tuberculosis and smallpox, and these illnesses had catastrophic effects on the mortality of the population. Rapanui reached its minimum size (111 individuals) in 1877 (Hernandez et al. 2000).
The political annexation of Easter Island by Chile in 1888 marked a new period of population recuperation and stabilized contact with foreigners. In 1893 the island became a sheep and cattle ranch under a concession given by the Chilean government, and this led to an influx of foreigners. The Rapanui native inhabitants were deprived of their rights and forbidden to leave the island under the excuse of leprosy control. Between 1914 and 1915, 50 German marines and some English prisoners were stranded on the island. Drapkin (1935), through an analysis of ABO blood groups, reported that the impact of these foreigners was noticeable. Demographic data showed that until 1965 the Rapanui were strongly endogamous, but after 1965 they were exposed to the modern world with resulting increased exogamy (Hernandez et al. 2000).
Polymorphisms on the nonrecombining segment of the human Y chromosome (NRPY) have been used extensively to infer migration events on both a global and a regional scale (Hurles et al. 2003; Hammer et al. 1998; Underhill et al. 2000; Kayser et al. 2001). The NRPY is uniparentally transmitted and escapes recombination; thus variation arises only by the sequential accumulation of new mutations along radiating paternal lineages. Recently, a substantial number of studies have used...
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