Consanguineous marriages and endemic malaria: Can inbreeding increase population fitness?

Department of Internal Medicine, Faculty of Medicine and Health Sciences, UAE University, PO Box 17666, Al Ain, Abu Dhabi, UAE.
Malaria Journal (Impact Factor: 3.11). 02/2008; 7(1):150. DOI: 10.1186/1475-2875-7-150
Source: PubMed


The practice of consanguineous marriages is widespread in countries with endemic malaria. In these regions, consanguinity increases the prevalence of alpha+-thalassemia, which is protective against malaria. However, it also causes an excessive mortality amongst the offspring due to an increase in homozygosis of recessive lethal alleles. The aim of this study was to explore the overall effects of inbreeding on the fitness of a population infested with malaria.
In a stochastic computer model of population growth, the sizes of inbred and outbred populations were compared. The model has been previously validated producing results for inbred populations that have agreed with analytical predictions. Survival likelihoods for different alpha+-thalassemia genotypes were obtained from the odds of severe forms of disease from a field study. Survivals were further estimated for different values of mortality from malaria.
Inbreeding increases the frequency of alpha+-thalassemia allele and the loss of life due to homozygosis of recessive lethal alleles; both are proportional to the coefficient of inbreeding and the frequency of alleles in population. Inbreeding-mediated decrease in mortality from malaria (produced via enhanced alpha+-thalassemia frequency) mitigates inbreeding-related increases in fatality (produced via increased homozygosity of recessive lethals). When the death rate due to malaria is high, the net effect of inbreeding is a reduction in the overall mortality of the population.
Consanguineous marriages may increase the overall fitness of populations with endemic malaria.

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Available from: Srdjan Denic
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    • "Several theoretical, animal and human studies have shown that, given the right conditions, inbreeding may sometimes increase relative fitness (Theodorou & Couvet, 2006;Denic et al., 2008;Helgason et al., 2008). For example, in theory, inbreeding accelerates selection of recessive beneficial alleles, increases the frequency of protective genotypes (such as alpha-thalassaemia, which is common in the study population), and increases survival in a given environment (such as during the time of heavy malaria infestation, which was endemic in UAE until one generation ago) (Denic et al., 2008). Finally, the inter-generational reversal of relative fertility of inbred and outbred families observed here might explain in part the conflicting results of fertility studies in consanguineous societies living under different environmental conditions (Bittles et al., 2002). "
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    ABSTRACT: Human consanguinity is often attributed to poverty, lack of education and social insecurity. Nevertheless, kin unions continue to be arranged in socioeconomically transformed societies. This study examined the structure of families and marriages in the rich tribal society of the United Arab Emirates, which has had a high gross domestic product for the last two generations and currently has one of the highest in the world. The respondents were 217 national medical students whose families are proportionally distributed to the population of the country emirates. The rate of parental consanguinity (defined as a union of any two cousins) was 36%. The social status and mean size of consanguineous and non-consanguineous families were not significantly different. In non-consanguineous families, polygamy was more common and the number of half-siblings per family was higher. The extended families were on average 7% larger among non-consanguineous families. In contrast, for the extended families of the participants’ grandparents, non-consanguineous families were smaller than their consanguineous counterparts. Participants from consanguineous families indicated that marriage of either a son or daughter was more difficult to arrange than did participants from non-consanguineous families. Though consanguineous parents had their offspring marry consanguineously more often than non-consanguineous parents, the numbers of married offspring in the two groups of families were not different. Consanguineous parents have more difficulty than non-consanguineous parents in finding spouses for themselves and for their offspring, and they arranged kin marriages for their children more often.
    Full-text · Article · Jan 2016 · Journal of Biosocial Science
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    • "inbreeding may accelerate the selection of protective genotypes against infections such as malaria (Caballero and Hill 1992; Denic et al. 2008). Additionally, consanguinity could further enhance the odds of survival for the family by providing better intra-family support and thereby protection against other causes of mortality (e.g. "
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    ABSTRACT: Despite being associated with multiple genetic problems, consanguineous marriages continue to remain extremely prevalent worldwide. Studying the variation of kin preferences in diverse inbred societies may provide some answers to this paradox. To find the reasons for specific kin choice in different geographical areas of the world. We used a set of sociobiological rules (kin altruism, sexuality and inbreeding avoidance) and ecological constraints (e.g. tribal warfare, food availability) that influence human behaviour. The cumulative help that the extended family can provide to a nuclear family was calculated using the coefficient of relatedness between kin in different types of consanguineous families. The maximum potential support for kin markedly varied between different types of consanguineous marriages. Overall, members of consanguineous families received up to two-and-half times more support than members of non-consanguineous families. In various inbred cultures, preference for a specific type of kin was determined by prevailing ecological limitations and sociobiological factors interacting in a complex manner. In different inbred populations, the ideal kin for a consanguineous marriage is the one who can provide the most altruistic support; however, this choice is influenced by biological rules of behaviour and ecological constraints.
    Full-text · Article · Mar 2010 · Annals of Human Biology
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    • "The cost-benefit ratio of inbreeding < 1.0 would encourage the practice of consanguinity. Transmission of consanguineous marriages, at least in the families that carry the allele, would result in a small gain in fitness, which in the long run would be compounded into a significant size advantage in an inbred population (Denic et al., 2008). "
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    ABSTRACT: Consanguineous unions are important because they are very common, accounting for approximately 10% of all marriages in the world. This prevalence is significantly higher than commonly perceived. Consanguinity is often associated with higher frequencies of congenital malformations and increased mortality among the offspring of such marriages. However, the harmful consequences of inbreeding may have been overestimated because the inherent taboos against consanguinity tend to bias the assessment of its genetic dangers. Inbreeding increases the speed of selection of many recessive and codominant alleles. Notably, among such alleles are α+-thalassemia, hemoglobin C, and Duffy antigen negative red blood cells, which protect against the death from malarial parasites. α+-Thalassemia, the most common monogenic condition in humans, is conspicuously superimposed on both geographic distributions of P. falciparum and high rates of consanguinity in populations, which suggests a causal link. Computer simulation studies have shown that in regions where malaria is prevalent, inbred populations with α+-thalassemia grow faster than outbred populations. Whether this faster growth compensates the excess of deaths in consanguineous populations due to harmful recessives remains to be determined. Nonetheless, it is possible that in these regions, consanguinity was genetically beneficial and evolved as a survival strategy – to counter high population mortality from malaria and perhaps other infectious diseases. In general,multiple social benefits are thought to be the reason for the persistence of high levels of consanguinity in populations. However, the social benefit theory does not explain why non-consanguineous societies, despite the same benefits, do not practice consanguinity. Furthermore, results of computer simulation of the genetic benefits of consanguinity fits into the historical conditions which existed during the agrarian revolution, when multiple epidemic infections emerged in rapidly enlarging populations. Besides malaria, this theory of genetic benefits is also applicable to many other infectious diseases like tuberculosis and HIV, the protection being due to the codominant MCP-1 and recessive CCR5Δ32 alleles, respectively. This article is an attempt to give a rational and objective view of consanguinity integrating different aspects from human genetics, history, psychology, anthropology and clinical medicine.
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