Today at lunch we were discussing the excellent movie, Walk The Line, which tells the story of the life of Johnny Cash. We were talking about another person portrayed in the film, Jerry Lee Lewis, who is notorious for having married his 13 year old cousin. We got to talking about the always fun topic of 'kissin cousins,' which led me to come back to the office and look up a bit about the subject. Here's what I found out.
In addition to Jerry Lee Lewis, Charles Darwin and Albert Einstein are also people who married their cousins. All three suffered for having violated a widely held social norm against "incestuous" unions. Yet there may be less reason for this norm, and for the laws enforcing it, than was once believed.
A panoply of state laws say cousin marriages are taboo. But a report in the Journal of Genetic Counseling concludes that cousins can have children together without running much greater risk than a "normal" couple of their children having genetic abnormalities. Accordingly, the report potentially undermines the primary justification for laws that prevent first cousins from marrying or engaging in sexual relations with one another. True, marriage among close kin can increase the chance of pathological recessive genes meeting up in some unlucky individual, with dire consequences. The problem isn't cousin marriage per se, however, but rather how many such genes are floating around in the family pool. If the pool's pretty clean, the likelihood of genetic defects resulting from cousin marriage is low. The report says that, on average, offspring of first-cousin unions have a 2 to 3 percent greater risk of birth defects than the general population, and a little over 4 percent greater risk of early death. While those margins aren't trivial, genetic testing and counseling can minimize the danger. An argument can be made that marriages of first cousins descended from strong stock can produce exceptional children.
The formerly high incidence of congenital defects, specifically hemophilia, among European royal families isn't the classic demonstration of the perils of inbreeding that everybody thinks it is. The short explanation is that hemophilia is an X-chromosome-related characteristic, transmitted only through the female line. The children of royal female carriers would have been at risk no matter whom their mothers had married.
The U.S. is virtually alone among developed nations in outlawing marriage among first cousins. European countries have no such prohibition. Even in the U.S. laws forbidding the practice are far from universal.
Twenty-four states prohibit marriages between first cousins, and another seven permit them only under special circumstances. For example:
- Utah permits first cousins to marry only provided both spouses are over age 65, or at least 55 with evidence of sterility. Arizona, Illinois, Indiana, and Wisconsin also have laws stating minimum ages or proof of sterility.
- North Carolina permits first cousins to marry unless they are "double first cousins" (cousins through more than one line. For instance, two brothers from one family marry two sisters from another; if each couple has a child, those offspring are double cousins).
- Maine permits first cousins to marry only upon presentation of a certificate of genetic counseling.
The remaining nineteen states, including New York and California, and the District of Columbia permit first-cousin marriages without restriction. All states allow marriage of second cousins or more-distant relatives.
So, how common are cousin marriages? Well, he frequency of cousin marriages in the USA is about 1 in 1,000. In comparison, the frequency of cousin marriages in Japan is about 4 in 1,000. It is estimated that 20 percent of all couples worldwide are first cousins. It is also estimated that 80 percent of all marriages historically have been between first cousins. And in some respects, we are all cousins, as no two people are more distantly related than 50th cousins.
So there you go.
This post flagrantly plagiarizes from: