According to the experts, marrying third and fourth cousins is so beneficial for reproduction because they have the "best of both worlds." While first-cousin marriages may have inbreeding issues, couples who are far apart may have genetic incompatibilities. The theory is that if two people are closely related, then their genes are likely similar, which will help them have children that are healthy and strong like themselves. On the other hand, people who are more distantly related tend to have more different genes, which gives their offspring a better chance of surviving into adulthood.
In most countries, including the United States, marriage laws allow any two people to marry, as long as they are not too closely or distantly related. If you are married to your cousin, you should understand that it is not illegal in the United States. However, many people feel uncomfortable with this relationship and might want to end it, so don't assume that just because you are married that you cannot be divorced.
In some cultures, such as that of the Inuit, people only marry within their families. This is called "in-family marriage" and it is common among people of Northern European descent. Since an Inuit man can have only four wives, this rule helps prevent men from accumulating too much power over others through marriage.
Third and fourth cousin weddings are the "best of both worlds," as the saying goes. They're dinnertime breakfast foods. You escape the inbreeding hazards associated with closer relatives, yet your genes are near enough that they naturally complement each other. In fact, scientists used to think that humans were genetically limited to marrying within 50 generations of ancestry. But new research shows that people can marry up to 160 years apart and still be genetically similar because modern technology allows us to compare entire genomes instead of just looking at a few dozen markers selected by evolution over many thousands of years.
That means that if you're willing to go to some pretty odd weddings, you can find someone who is almost a perfect genetic match for you. It's all about finding those distant cousins who happen to be living near each other.
It's estimated that one in every eight marriages in the United States is between spouses who are third or fourth cousins. That number is high because researchers assume that these couples have not restricted themselves to only marrying within their shared group. Instead, they've included spouses from different branches of the same family tree in order to maximize the chances of finding matches with similar genetic traits.
Even so, third-and fourth-cousin marriages are relatively rare. For example, in studies of people of European descent like those listed above, this type of marriage occurs about 1 out of 20 times.
Marriage to a cousin who is your second cousin or older is lawful in all 50 states. In fact, scientists used to believe that anyone who could trace their ancestry back three generations was related by blood. Now we know better - our ancestors were mostly farmers, foragers, and builders who had many more partners than just these two people. But three generations is enough to make a significant genetic contribution from both parents.
In some countries, such as England and Australia, marrying within certain degrees of kinship is allowed without legal consequences. In America, however, only marriages between persons who are not closely related are valid, so if you're looking to import a marriage license from another country, be sure to find out how close the relationship has to be.
Closer relationships are also possible. The offspring of two first cousins have a one in four chance of being born with a serious disease called cystic fibrosis. Yet because of advances in medical technology, most such births now survive into adulthood. A couple who is second cousins once removed can expect an infant mortality rate of about five in every 100 births. Yet because most such deaths aren't reported, the true figure may be higher or lower than this number suggests.
Inbreeding may lead to dangerous genetic problems, hence marrying a cousin is typically regarded a poor decision. However, evidence reveals that in certain civilizations, marrying a related spouse is associated with having more surviving offspring. In some cases, the spouses are actually first cousins who would not otherwise have children. So although marrying a cousin is generally not recommended, this arrangement might be acceptable under certain circumstances.
In most societies, marrying within one's blood group or even caste is expected. Citing religious reasons is also common. However, research has shown that in some Indian villages, where many people belong to several different castes, marrying outside one's own caste increases the chances of having children with an inherited disease.
In some cultures, consanguineous marriages are accepted, while in others they are not. Legal restrictions may vary from country to country. For example, in some countries siblings are forbidden to marry, but other relatives such as parents, grandparents, uncles, aunts, and cousins are usually allowed to marry each other. Even within countries, legal distinctions can exist between different regions. For example, in some states of the United States of America (USA) marriages between first cousins are illegal, while in others they are not.
Marriage between cousins is common in certain parts of the world.