Population evolution in 20th-century Easter Island: Endogamy and admixture

We studied the 20th-century evolution of the Rapanui population of Easter I sland, the most geographically isolated in the world, to analyze the curren t process of admixture. Using parochial birth records, we determined origin of the birth parents based on their surnames. The origin of parents reveal s two stages of population evolution: endogamy, due to the isolation of the island, but with a strong rejection of isonymous marriages; and admixture, beginning in 1965 with the opening of the island to the rest of the world. We used Lasker's coefficient (Lasker's R-i) and the Shannon-Weaver coeffic ient of diversity (H) to characterize both stages, The gene flow evaluated from admixture has increased significantly since 1965. Births from exogamou s unions represented 3.5% of total births from 1937 to 1965, increased to 4 3.2% between 1966 and 1980, and constituted 50.8% of all births between 198 1 and 1996.