It is also notable in its own right that in parts of Southern Italy in the late 20th century, more than 50% of marriages were to a cousin.
Norms of nepotism and favoritism create corruption, subverting and disrupting impartial institutions and hampering economic development. However, the presence and strength of such norms varies widely within and between countries, and the literature has suggested that this variation is driven, in part, by ethnic fractionalization, with mixed results.
We provide evidence for an overlooked -- but deep-rooted -- source of variation in corruption: sub-ethnic fractionalization, driven by mating patterns. The theory of kin selection provides a straightforward justification for norms of nepotism and favoritism among relatives; more subtly, it also implies that the returns to such norms may be influenced by mating practices.
Specifically, in societies with high levels of sub-ethnic fractionalization, where endogamous (and consanguineous) mating within kin-group, clan and tribe increases the local relatedness of individuals, the relative returns to norms of nepotism and favoritism are high. In societies with exogamous marriage practices, the relative returns to norms of impartial cooperation with non-relatives and strangers are increased.
Using cross-country and within-country regression analyses and a cross-country lab experiment, we provide evidence for this account. Our cross-country analyses show that corruption levels are robustly associated with consanguineous marriage rates, even when controlling for previously studied deep determinants of comparative development. Our within-country analysis exploits variation in consanguinity across Italian provinces and identifies the same pattern. Lab experiments in two countries with different mating patterns provide evidence for our proposed mechanism from subjects who interacted with kin, co-ethnics and strangers in a stylized corruption game.Mahsa Akbai, et al., "Kinship, Fractionalization and Corruption" (October 3, 2016).
[G]eography- and culture-driven population division are the most common sources of sub-ethnic fractionalization. The influence of geography on population division should be obvious; as populations migrated around the world historically, they became isolated from one another due to vast distances and geographic barriers such as mountains, deserts and oceans that were only recently broken down by transportation technologies. Due to isolation, some groups accumulated relatively high local relatedness.
However, our focus will be on culture-driven population division, in particular on the role of cultural preferences for and prohibitions of certain mating practices, which, when permitted, favor sub-ethnic fractionalization and thereby raise the relative returns to norms of favoritism and corruption. One mating practice that directly increases local relatedness and encourages sub-ethnic fractionalization is a preference for consanguineous marriage, most prominently among cousins. In a cross-cultural ethnographic tabulation due to Murdock (1967) and Gray (1998), a total of 476 out of 1024 societies for which we have data either permitted or favored first and/or second cousin marriage, and estimates suggest that roughly 10% of marriages around the world today are consanguineous (Bittles, 2012).
While the negative health effects of consanguinity are well-known (e.g. increased risk of autosomal-recessive disorders), some believe that there are countervailing positive effects as well (Jaber et al., 1998). In a small sample, genomic estimates of the “inbreeding coefficient”, which measures “the proportion of a genome that is ‘autozygous’ - homozygous for alleles inherited identically by descent from a common ancestor,” are correlated as expected with consanguineous marriage rates (r = 0.349, p-value = 0.04, N = 26). The correlation would likely be higher except that the genomic measures also capture background (so-called “cryptic”) inbreeding.
The wide diversity in attitudes towards consanguinity in human societies partially originates in religious beliefs due to the common jurisdiction of religious institutions over marriage. . . . Of particular note are the fact that the Catholic Church has placed restrictions on cousin marriage since at least 500AD (sometimes extending these bans out to sixth cousins) and the fact that a persistent preference for cousin marriage can be seen in many Islamic countries, at rates as high as 50% of marriages. . . .
However, religion is not the only source of variation, and marriage norms may be particularly persistent, even as religious attitudes change. As one example, consanguineous marriage has long been prevalent in parts of Italy, despite it being an almost entirely Catholic country. Cavalli Sforza et al. (2004) suggest this may be a result of persistent cultural norms imported during the Arab conquest of southern Italy over 1000 years ago. Going the other direction, majority Protestant countries mostly legalized cousin marriage after centuries of living under the Catholic ban. Nevertheless, consanguinity remains rare in those countries. In the United States, cousin marriage is illegal in 25 states, though its frequency remains low even where it is legal.
Others have argued that consanguinity is a cultural adaptation to social and ecological circumstances. In his history of the family, Goody (1983) suggests that consanguinity may be a property and wealth-preserving response to gender-egalitarian inheritance rules, which encourage the diffusion of property through out-marriage due to geographical population division (Pemberton and Rosenberg, 2014, p. 38).
A few studies have examined the causes and consequences of consanguinity in small-scale societies using detailed genealogies to directly measure relatedness. Walker and Bailey (2014) show that among forager peoples, such marriages are rare due to norms of exogamy and fission/fusion dynamics that disperse kin across groups, but among agropastoralists, particularly those that practice polygyny, the practice is more common, with average spousal relatedness rising as high as r = 0.18 (almost 50% greater than first cousins, r = 0.125). Using log(surviving children) as a measure of fitness, estimates in Bailey et al. (2014) suggest that these marriage practices may be adaptive, with fitness maximized for moderate consanguinity among agropastoralists and with minimal consanguinity among foragers. Other evidence from Hoben et al. (2010) suggests that consanguinity may be more prevalent near the equator since it can raise the frequency of homozygosity for adaptive recessive mutations that defend against diseases and parasites, which are also more prevalent in warmer climes.
Regardless of its diverse origins, wherever it is practiced, consanguineous marriage directly increases local relatedness and encourages fractionalization, thereby altering the returns to norms of favoritism and norms of impartial cooperation. Thus, variation in consanguinity rates facilitates a test of our main hypothesis: that sub-ethnic fractionalization causes corruption. To reiterate, our argument is that consanguinity increases incentives for kin altruism and hence for corruption, but the mechanism needn’t be genetic. That is, while it might be possible to show that differential selection pressures resulting from persistent inbreeding could increase the relative frequency of “altruistic alleles” favoring kin altruism, genetic change (or genetic difference) is not necessary to explain a change in the relative importance of kin altruism (and consequent corruption) across groups. Instead, we assume that all humans possess the capacity for kin altruism as well as for cooperation with non-kin, and that the norms operating in any given society merely favor one or the other mechanism of cooperation, to varying degrees.
Since humans are social creatures reliant on cultural norms of cooperation and information-sharing for survival, selection pressures also operate on these norms, so that a society’s norms adapt to local conditions (Henrich, 2015). Thus, different mating patterns (due to culture or geography) may raise (or lower) the relative returns to norms of nepotism and local favoritism on the one hand and norms of impartiality, impersonal exchange and reciprocity on the other hand.
For instance, in countries Christianized for at least 500 years (and long-exposed to consanguinity bans), we see a significant decrease in the importance of clans and lineage groups (Greif, 2006). Moreover, cultural change and changes in local relatedness may be self-reinforcing. Historically, bans on consanguineous marriage were an important cause of migration, especially in agricultural societies where one male child inherited the family’s land. Siblings without property, especially females, had to migrate to find marriageable men (Cavalli-Sforza et al., 2004). This exchange of people across distances may have increased the returns to impartial norms facilitating peaceful interaction with strangers, perhaps in the long run encouraging the development of large-scale institutions based on generalized trust, such as markets, which also facilitate out-marriage.
Inducements to consanguinity (or absence of a ban) may have opposite effects. By shrinking the sphere of social interaction to a group of more closely related people, consanguinity may encourage norms of partiality and in-group favoritism, and such norms may be readily applied to affines and other fictive kin, generating tight-knit local groups at the expense of potential impartial and impersonal arrangements that would expand the possibilities for exchange more broadly. Moreover, the presence of these relatively higher returns could have an amplifying effect, further raising the incentive to consanguineous marriage; see Jones (2016) on feedback between social norms and kin altruism.
Our argument is related to the literature that distinguishes between generalized morality and limited morality (or amoral familism) (Banfield, 1958; Platteau, 2000; Tabellini et al., 2008). Limited morality is the extreme reliance on a narrow circle of family, friends or relatives; outside this circle, harming and cheating are allowed and frequent. In this narrow circle, people are raised to trust in-group members only. They are also taught to distrust people outside the circle, which hampers cooperation and exchange with strangers and outsiders, and as a result, impedes the development of formal institutions. Generalized morality is characterized by respect for abstract individuals and their rights, generalized trust and loyalty to general rules, which facilitates large-scale cooperation. The underlying mechanism that determines whether a society adopts limited morality has been attributed to strong versus weak family ties (Ermisch and Gambetta, 2010; Alesina and Giuliano, 2011, 2014), collectivism versus individualism (Yamagishi and Yamagishi, 1994; Yamagishi et al., 1998), and clan versus corporation (Greif and Tabellini, 2015; Greif, 2006). We also contribute to this literature highlighting another mechanism: sub-ethnic fractionalization increases the relative returns to limited morality and therefore encourages corruption.According to their international regression model "a 1 standard deviation increase in consanguinity is associated with a reduction in quality of governance (i.e. increase in corruption) by about 0.75 standard deviations." Lower per capita income is also associated with corruption and explains almost all corruption effects otherwise attributable to geographical latitude.
A preference for consanguineous marriage is common in the Islamic world, and thus consanguinity rates and the percent of the country practicing Islam are highly correlated (Spearman’s ρ = 0.73, p-value < 0.001, N=67). In contrast, Catholicism has imposed a long-standing ban on consanguineous marriage, and this is evinced by a strong negative correlation between the share of a country practicing Catholicism and consanguinity (Spearman’s ρ = -0.57, p-value < 0.001, N=67). Finally, while Protestant religions do not officially ban consanguineous marriage, the frequency is quite low, and we find a large negative correlation between a country’s share of Protestants and consanguinity (Spearman’s ρ = -0.53, p-value < 0.001, N=67).
Meanwhile, political identity and group affiliations remain a dominant factor in American politics.
Does cousin marriage play a role in red state; blue state politics?
A list of states where cousin marriage is legal (per Wikipedia below) shows no clear red state, blue state pattern, but legality may not track the actual frequency of cousin marriage in the United States.
This is mostly because social factors keep the percentage of cousin marriages very low for the most part.
This is mostly because social factors keep the percentage of cousin marriages very low for the most part.
For the United States as a whole, the cousin marriage rate is about 0.2% (so there are about 250,000 people in these relationships), based mostly on old and not completely reliable data that are still unlikely to be wildly wrong, but "if you take a global perspective, consanguinity is not rare at all. Of the 70 countries studied, only 18 have consanguineous relationships as less than 1 percent of all marriages. In five countries, more than 50 percent of all marriages are between people who are second cousins or closer, and in Burkina Faso, it’s estimated that two of every three marriages are consanguineous."