Secular trends in the relationship between surnames in a population: Study of a border town

The study of surnames in a territory over time is an opportunity to obtain knowledge of the evolution of allelic frequencies. Geographic and cultural factors influence the renovation of surnames and reflect accelerations or delays in the gene flow. Political borders may also condition the genetic structure of a population. Using isonymy, this paper studies the evolution (from 1750 to 2006) of the frequencies of surnames and the components of inbreeding in Olivenza, a border town whose sovereignty was transferred from Portugal to Spain in 1801. After the change in dominion the number of Portuguese surnames fell sharply and the expected values for a population so close to Portugal recovered only after a long period of time. The results indicate that although the border has made population movement more difficult, and has therefore had an impact on the rate of gene exchange, a certain gene flow with Portugal persisted.