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SummaryNatural selection and genetic drift are two evolutionary mechanisms that can be analysed in human populations using their fertility and mortality patterns, and their reproductive size and isolation, respectively. This paper analyses the models of natural selection and genetic drift in Bayárcal, south-east Spain, and compares them with the observed models in the rest of the Alpujarran region. Demographic data were obtained from a sample of 77 families (48.45% of the population, with 547 inhabitants). The genetic drift and natural selection action was evaluated with the Coefficient of Breeding Isolation (CBI of Lasker and Kaplan) and Crow's index, respectively. The CBI (23.23/12.61) suggests that genetic drift is near to acting, and Crow's index (I=0.58) is slightly higher than that observed in the rest of La Alpujarra. Although the reproductive isolation of Bayárcal is not effective enough for genetic drift to act, it is near when marital migrants inside the Bayárcal valley are considered as a native population. The natural selection pattern is not different from that of the rest of La Alpujarra, but it tends towards the model of developing communities, where the demographic transition has not yet begun. [ABSTRACT FROM AUTHOR]

This paper assesses the reproductive and abortion patterns of women living in Plaza de la Revolución, a municipality of Havana, Cuba, by studying the factors influencing birth and abortion rates. Socio-demographic data and female reproductive histories were collected in a survey of 1200 post-menopausal women living in the municipality. Average ages at menarche and at menopause were 12.71 and 48.39 years, respectively, thus yielding a potential long reproductive period of 35.68 years, indicating high fertility. Although the mean pregnancy rate was 3.81 pregnancies per woman, the live birth rate at time of delivery was only 1.89 due to the high rate of abortions: 40% of all pregnancies were voluntarily interrupted. Among the biological and socio-cultural variables that were found to influence the rate of live births were those related marriage pattern, especially age at first union. Demographic variables such as pregnancy order, maternal age and marital status were the main determinants of the abortion pattern, with abortion being used as a method of birth control in order to obtain the desired family size, and most women (75.2%) using contraceptives.