Conservatism and Inbreeding

Humans generally leave more descendants if they marry someone who is not too closely related. So highly inbred royal families experience many genetic disorders like hemophilia. Inbreeding is connected to the liberal-conservative continuum.

The health issues of royal families are a case of disease genes being inherited from both parents. Such genes are mostly rare and are usually masked by receipt of a “healthy” gene from one parent. Because royals are mostly highly inbred, both parents share many genes, including recessive disease-promoting ones.

Slight inbreeding has advantages, however. Parents who are too genetically different from each other may have trouble raising viable offspring.

This can happen when one parent migrates into a region for which their immune-system genes are poorly adapted so that the offspring are sickly. Another example involves blood-group incompatibility between both parents—a problem where the mother's body mounts an immune reaction to the fetus.

Between inbreeding depression and outbreeding depression, there is an optimal level of outbreeding that varies between species.

Among birds, females migrate at maturity and different species travel different distances as a way of avoiding a pairing with a mate who is closely related.

Even modern humans behave similarly. We generally prefer to mate with others who are like ourselves both by belonging to the same ethnic group and also being similar in social status and where we exist on the political liberal-conservative spectrum.

Optimal Outbreeding

Denmark has exceptionally good public records of births and marriages going back for centuries making it ideal for studying outbreeding in the population. Researchers found that Danes mostly marry someone who was born in parishes 20-120 kilometers from their home parish (averaging about 30 miles) apart (1).

This is remarkable, even for such a small country. In practice, it means that they travel just far enough to avoid mating with genetically similar individuals but not far enough to experience outbreeding depression. While no one is likely to marry an aunt or uncle, in an inbred population, it is possible to marry someone who is genetically very similar despite being a stranger.

Danes who married a spouse 70 kilometers away produced more children than those who had either a shorter or longer trek to the spouse's home parish.

This is clearly a case of optimal outbreeding. Other evidence suggests that married couples who have similar relatedness to second cousins leave the most second-generation descendants (2). This helps explain why cousin marriages are often preferred in societies studied by anthropologists even though they are banned in some developed countries.

Individuals who migrate long distances to find a mate are clearly more open to experience than stay-at-homes. Such openness is linked to political orientation in complex ways (2).

Inbreeding and Tribalism

Being more closely attached to one's family, ethnic group, and place of birth is sometimes referred to as tribalism. This tendency affects political orientation. For example, conservative opposition to immigration reflects xenophobia whereas the liberal acceptance of other ethnic groups is xenophilia.

To the extent that xenophobia reflects fear of the unknown, it may be considered a mechanism for avoiding outbreeding depression. Conversely, the liberal openness to other ethnicities can be considered a mechanism for avoidance of inbreeding. According to this view, human variation in openness could have arisen as a means of selecting for variation in outbreeding.

Although supported by a variety of evidence in neuroscience, personality, and genetics these ideas are downplayed because they evoke eugenics scandals of history (2).

Tribalism and Conservatism

Conservatives are family oriented and celebrate the groups to which they belong. Conversely, they are less open to new experiences and people of diverse backgrounds that fuels antagonism towards immigrant groups. Such propensities favor mating with others from the community and prevent extreme, and possibly deleterious, outbreeding.

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Favoring one's own family can mean monopolizing resources such as land and wealth that may be inherited by subsequent generations. This orientation would be favored by evolution in environments where resources are scarce. This helps explain why people become more conservative during difficult economic times.

To the extent that monopolizing resources may harm the interests of out groups, it feeds intergroup friction. It also goes along with a mindset that the world is a harshly competitive place populated with winners and losers. Conservatives thus find it easier to justify stark income inequality than liberals do (2).

Controversial as these ideas may be, they have the merit of combining a great deal of evidence from different disciplines into a coherent evolutionary framework. That is a great starting point for researchers.