Steven Pinker's "Inherit the Wind: Our Weird Obsession with Genealogy" is the cover story in\ the August 6, 2007 issue of The New Republic. Here's an excerpt:
In the struggle between society and family, the exponential mathematics of kinship ordinarily works to the advantage of society. As time passes or groups get larger, family trees intertwine, dynasties dissipate, and nepotistic emotions get diluted. But families can defend themselves with a potent tactic: they can graft the twig tips of the family tree together by cousin marriage. If you force your daughter to marry her first cousin, then your son-in-law is your nephew, her father-inlaw is your brother, your parents’ estate will be worth twice as much per grandchild, and the couple will never have to bicker about which side of the family to visit on holidays. For these reasons, clans and dynasties in many cultures encourage first-or second-cousin marriage, tolerating the slightly elevated risk of genetic disease. Not only does cousin marriage amplify the average degree of relatedness among members of the clan, but it enmeshes them in a network of triangular relationships, with kinsmen valuing each other because of their many mutual kin as well as their own relatedness. As a result, the extended family, clan, or tribe can emerge as a powerfully cohesive bloc—and one with little common cause with other families, clans, or tribes in the larger polity that comprises them. The anthropologist Nancy Thornhill has shown that the prohibitions against incestuous marriages in most societies are not public-health measures aimed at reducing birth defects but the society’s way of fighting back against extended families.
In January 2003, during the buildup to the war in
Overall, Pinker does an excellent job of synthesizing what I've been writing for years, with one lacuna, which I'll explain at another time.