Go ahead, marry your cousin—it's not that bad for your future kids Just don't turn it into a family tradition. By Eleanor Cummins posted Mar 5th, at They were related through both maternal and paternal lineages: Their mothers were sisters and their fathers were first cousins. Wikimedia Commons Yaniv Erlich has a soft spot for genealogy. A data scientist at Columbia University and the chief science of officer of the DNA test company MyHeritage, he describes many things in the context of family.
Among other things, the researchers were able to determine at what point in history marrying your cousin went out of vogue, and the average degree of relation between married couples today. And scientific geniuses like Albert Einstein and Charles Darwin married their cousins, too. But within a century, that had changed. By , married couples were, on average, more like seventh cousins, according to Erlich.
One common sense explanation for this shift is that when transportation methods improved, bachelors and bachelorettes had access to potential partners they had once been denied by geography. This makes sense, given that before , most people stayed in place and ended up marrying someone who lived with in a six-mile radius of where they were born. Other factors could be at play, however.
Erlich says that, according to his data, many continued to marry their cousins even after the Industrial Revolution dramatically improved mobility. While proximity may be one key to romance, it seems consolidating money or power played an important part in family marriages, too. Erlich believes it was changing social norms—and the advent of this cousin marriage taboo—that finally pushed people to look beyond their village and their family. Other factors, including the increasing autonomy of women and shrinking family sizes which left fewer cousins to marry could also have been involved.
Whatever the underlying cause, by the end of the Civil War , many states moved to outlaw cousin marriages. Today, 24 states ban marriage between first cousins, while 20 states allow it. The others allow first cousins to couple up, but only under certain circumstances. And, of course, even in states where it is legal, the practice is taboo.
Dark blue marks states, like California, where first-cousin marriage is legal. Light blue, like Maine, represents states where cousin marriage is legal with some requirements or exceptions.
Light red, like Illinois, is banned with exceptions. Dark red, like Washington state, is a total ban on first-cousin marriage. And blood red, like Texas, means marrying your cousin is a criminal offense. Wikimedia Commons First cousins share Siblings, as well as parents and kids, share about 50 percent. Any child that results from a first cousin union is, therefore, going to have a pretty substantial portion of similar-looking genes. And that can pose a problem. In biology, genetic diversity is all the rage.
If mom and dad are genetically similar, however, both versions of a gene are likely to shut down at the same time. The real issue would arise if the next generation of kids also married their first cousins.
Their offspring will have even more DNA in common—and an even greater chance for birth defects. There are plenty of historical examples of this. Charles II, the last Hapsburg king, had so many intermarried ancestors that his genes seemed more like the product of a union between siblings than the reality of uncle marrying niece.
Ultimately, marrying your first cousin carries some risk. But the odds of healthy offspring dramatically improve with each new distance of relation. Second cousins share only 6. Seventh cousins—the average distance between modern American spouses—have no meaningful genetic relation at all.
The genetic data, branching off this way and that, reveals just how closely related we all already are.