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: 3.49). 02/2008; 7:150. DOI: 10.1186/1475-2875-7-150
Source: PubMed

ABSTRACT 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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    ABSTRACT: Historically, medical concerns about the deleterious effects of closely inbred marriages have focused on the risk posed by recessive Mendelian disease, with much less attention to developmental instability. We studied the effects of inbreeding (first-cousin marriage) on growth and fluctuating asymmetry of 200 full-term infants (101 inbred and 99 outbred) whose parents were of similar socioeconomic status in Sivas Province, Turkey. In addition to differences in their mean inbreeding coefficients (f = 1/16 for first cousins and f < 1/1,024 for unrelated parents), the consanguineous parents were less well educated (3 years, on average for both husbands and wives). We measured weight, height, head circumference, and chest circumference of the newborns, as well as four bilateral traits (ear width, ear length, and second and fourth digit lengths). After taking education into account, none of the measures of size (weight, height, head circumference, and chest circumference) and fluctuating asymmetry differed between the inbred and outbred groups. Male children of well-educated parents, however, were larger and had less fluctuating asymmetry. Female children of well-educated parents weighed more than those of less well-educated parents, but were otherwise indistinguishable for height, head circumference, chest circumference, and fluctuating asymmetry. We conclude that inbreeding depression causes neither an increase in fluctuating asymmetry of full-term newborns, nor a decrease in body size. Unmeasured variables correlated with education appear to have an effect on fluctuating asymmetry and size of male children and only a weak effect on size (weight) of female children. Am J Phys Anthropol 153:45-51, 2014. © 2013 Wiley Periodicals, Inc.
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    ABSTRACT: Whenever biologically unrelated mates become scarce, consanguineous marriages become a potential option for procreation. Despite the genetic harms caused by inbreeding, kin unions still produce more viable offspring than the alternative: remaining single. We present a family that, due to loss of its high social status, was unable to find unrelated mates for their children. The solution was a marriage arranged between first cousins, which produced five children with genetic disorders. By the time these defective children became adults, the social status of the family improved. Thus, for their four unfit daughters, the parents could arrange marriages with healthy and biologically unrelated men. These unions produced four healthy children. We analyze the interaction of mate choice, sexuality, inbreeding avoidance, altruism and parental investment to establish that close-kin marriages are an adaptive response to a shortage of unrelated mates.
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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.
    Advances in Sociology Research, Edited by Jared A. Jaworski, 01/2009: chapter On Differing Aspects and Perception of Consanguineous Marriages; Nova Science Publishers, Inc.., ISBN: 978-1-60741-879-5