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Consanguinity of human populations can but does not have to be associated with increased fertility. A recent study involving communities of Northeast Brazil revealed increased levels of endogamy.Data from 20 451 interviewed couples and their 74 289 children were analysed.The present study aimed to compare fertility between consanguineous and unrelated couples of these communities.Consanguineous and unrelated couples of the 39 communities had an average of 4.3 (SD = 0.9) and 3.5 (SD = 0.8) children (p 0.0001), respectively. Average offspring number of consanguineous couples varied from 3.9 (SD = 1.1) to 5.6 (SD = 3.4) for couples related at the level of third cousins and double first cousin/uncle-niece, respectively (p 0.005). The correlation coefficient between Human Development Index and fertility was -0.38 (p = 0.0179) and -0.23 (p = 0.17) for unrelated and related couples, respectively.Results indicated an overall positive association between consanguinity and fertility. Fertility tended to be increased, for closely related couples, compared to those related more distantly.

Using a family reconstitution study the biology of the plague in Penrith, Cumbria in 1597/8 is described in detail; it was an explosive epidemic that spread rapidly within families and 606 individuals died of the plague, some 40% of the population. The age-specific mortality corresponded with the calculated age structure of the population and infection appeared to be random. The sex ratio of victims was 1.37 females to 1 male. The plague spread from the northeast via Richmond and then exploded in the Eden valley, appearing almost simultaneously in Penrith, Kendal and Carlisle. The details of the epidemics and the location and the climate of these widely separated small market towns show that bubonic plague was not the causative agent, and the possibility that anthrax was responsible for the drastic mortality is briefly considered. The population rapidly built up after the plague, largely by immigration and not by increased fertility, and steady-state conditions were re-established within 5 years and continued for 150 years. This severe mortality crisis of the plague had a profound effect on the population at Penrith, triggering long wavelength oscillations in both baptisms and burials in this population living under marginal conditions and maintained in steady-state by density-dependent factors.

SummaryThe demographic correlates of modernization were studied in a municipio of the Guatemalan highlands using, as indicators of modernization, the introduction of chemical fertilizers and of a religious revitalization movement, Accion Catolica. Records, taken from interviews, of 340 women divided into declines (decennial groups) within ten-year birth cohorts extending from before 1925 to 1954, were checked for representativeness against the birth registries for the entire municipio for the years 1965–69.A steady decrease in the age of marriage of successive cohorts, based on probits, from 17·4 to 14·2 years, occurred, and the age at first birth declined from 20·9 to 15·9 years. There has also been a steady increase in the mean number of livebirths so that, e.g., the 10–19 year decline of the youngest cohort has more than doubled the number of live births of the same decline among the oldest cohort. Pre-school mortality of children has fallen drastically which, combined with increased fertility, has res...