摘要：In this work, twinning and illegitimacy rates are analyzed in a rural community from the Basque Country (Lanciego, Rioja Alavesa, Spain) based on 13 298 parish records (baptism certificates). The period examined in our study spans about two centuries (1800-1990). The estimate of the dizygotic twinning rate (per 1000 livebirths) using the Weinberg method ( d = 6,02) falls within the rank reported for Spanish rural populations (4,25-8,68), while the monozygotic twinning rate calculated for Lanciego ( m = 3,38) is above the variation rank referred in previous studies (0,57-2,49). However, global twinning rate (for the whole study period) was 9,48, a figure that is practically equal to the Spanish mean (9,50). On the other hand, the global illegitimacy rate in Lanciego (1,13%) was markedly lower than observed in other Spanish rural communities, where values above 10% have been reported. From this finding it can be deduced that births out of marriage do not seem to have a relevant selective role in the study population.
