No abstract

We propose that consanguineous marriages arise adaptively in response to high parasite prevalence and function to maintain coadapted gene complexes and associated local adaptation that defend against local pathogens. Therefore, a greater prevalence of inbreeding by consanguineous marriage is expected in geographical regions that historically have had high levels of disease-causing parasites. Eventually such marriages may, under the contemporary high movement of people with modern transportation, jeopardize the immunity of those who practice inbreeding as this leads to an increased susceptibility to novel pathogens. Therefore, a greater frequency of inbreeding is expected to predict higher levels of contemporary mortality and morbidity from infectious diseases. This parasite model of human inbreeding was supported by an analysis involving 72 countries worldwide. We found that historically high levels of pathogen prevalence were related positively to the proportion of consanguineous marriages, and that a higher prevalence of such marriages was associated with higher contemporary mortality and morbidity due to pathogens. Our study addresses plausible alternative explanations. The results suggest that consanguineous marriage is an adaptive consequence of historical pathogen ecologies, but is maladaptive in contemporary disease ecologies.

Little is known about current attitudes towards cousin marriages. Using data from a rural population in the Mexican state of Oaxaca, the present research examined how life history was related to attitudes towards cousin marriages in various ethnic groups. Participants were 205 parents from three ethnic groups. i.e., Mestizos (people of mixed descent, n = 103), indigenous Mixtecs (n = 65), and Blacks (n = 35). Nearly all men in this study were farm workers or fishermen. Participants reported more negative than positive attitudes towards cousin marriage, and women reported more negative attitudes than did men. The main objection against marrying a cousin was that it is wrong for religious reasons, whereas the risk of genetic defects was considered relatively unimportant. Cousin marriage was not considered to contribute to the quality and unity of marriage and the family. The three ethnic groups did not differ in their attitude towards cousin marriages. However, a slower life history was related to a more negative attitude towards cousin marriages, especially among Blacks, less so among Mixtecs, and not at all among Mestizos. In addition, and independent of the effect of life history, with increasing levels of parental control over mate choice, the attitude towards cousin marriage was more positive, but among men the attitude was more negative the more religious they were. The results are discussed in the context of theorizing on life history theory and the benefits and costs of cousin marriages.

The purpose of this study is to examine variance in the practice and acceptance of cousin marriage in select areas of the world. This study uses Murdock's Standard Cross Cultural Sample (SCCS). The SCCS includes 186 societies ranging from contemporary hunter and gatherers to early historic states to contemporary industrial people. It is hypothesized that cousin marriages are more likely to occur in small, isolated communities, and in communities that experience high rates of pathogen prevalence. That is, the variance in the practice of cousin marriage may reflect functional responses to various local ecological and environmental pressures. The results demonstrate that geographic isolation and pathogen prevalence are both independent and significant positive predictors of whether or not a society practices cousin marriage. These findings suggest that consanguineous marriage may be an adaptive solution to the problem of mate selection, depending on the environment in which one lives. Consequently, the biological advantages may lead to and/or become an individual preference, which is then reinforced by the local culture. We contend that although social and cultural explanations are of obvious importance, they can only provide partial explanations, and much can be gained from incorporating an evolutionary perspective.

Men are generally more distressed by a partner's sexual infidelity whereas women are generally more distressed by a partner's emotional infidelity. The importance of the identity of the interloper, however, has been neglected. We explored the influence of relational proximity (i.e., the degree of genetic relatedness) on distress about infidelity. In Study 1, participants were most distressed when the imagined infidelity occurred between their current mate and close kin. In Study 2, relational proximity mattered more than the type of sexual behavior, the likelihood of contracting a sexually transmitted disease, and the likelihood of the infidelity leading to a damaged reputation. Together, the results indicate that identity matters, especially if the interloper is someone with whom we have familial bonds.