Incidence of ecological factors on the evolution of infant mortality in a Mediterranean population (La Alpujarra, SE Spain)

A study using demographic data of genetic drift and natural selection in an isolated Mediterranean community: Bayárcal (La Alpujarra, south-east Spain)

Natural 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.

Seventy-three nuclear DNA polymorphisms in a Spanish population and a comparison with ten other populations

An anthropologically well-defined Spanish sample from La Alpujarra (SE Spain) was analyzed for 73 nuclear DNA polymorphisms. The population was chosen on the basis of available information on its history and demographic characteristics making it suitable for comparisons with data from North African populations. The Moslem invasion in this area was longer than anywhere in the Iberian Peninsula (more than nine centuries). The markers analyzed have been studied previously in 10 human populations from different continents. The Alpujarrenian population was checked for these markers and it is the one with the highest number of chromosomes analyzed. Two new alleles were sized and heterozygosity levels were very similar to other European populations. Genetic distances closely matched geographical relationships both with neighbor joining tree and principal component analysis. Allele distributions revealed specific associations with some populations. This work reveals the importance of these markers for evolutionary studies of human populations.

Inbreeding incidence on biological fitness in an isolated mediterranean population: La Alta Alpujarra Oriental (southeastern Spain)

The incidence of parental inbreeding on biological fitness was analysed in a sample of the Alpujarrenian population. Fitness was estimated as the fertility and offspring viability from conception to reproductive age. The analysed sample represents about 45% of the population from the Alta Alpujarra Oriental in southeastern Spain, and includes 847 families and 2916 pregnancies. The results showed slightly higher reproduction in consanguineous marriages, but the differences observed were not statistically significant. Higher pregnancy numbers are usually interpreted as stemming from greater immunological compatibility of the mother and foetus and may also reflect the significantly higher early foetal viability in this population. According to other authors, the great number of births observed in Alpujarrenian consanguineous marriages is, in part, a reproductive compensation for increased perinatal and neonatal mortality found as a possible negative result of homozygous combinations of deleterious alleles.

Reproductive pattern in a rural Mediterranean population: La Alpujarra, Spain

The reproductive pattern of a sample of nuclear families from La Alpujarra (Andalusia, Spain) is analysed. The origin of the wife or consanguinity of the couple does not influence fertility. Variability in number of pregnancies is most closely associated with marriage duration followed by the wife's year of birth. Differences in the number of births are explained more by the number of pregnancies than by the number of miscarriages. The number of survivors to the first birthday is dependent on the number of births and to a lower extent on infant mortality. Data from incomplete families show that reproductive performance of the wife below the age of 45 cannot be accepted as a reliable estimate of complete reproduction.