Reasons cousin marriage is illegal in some places


There are some people out there–specifically the ones who are against sexual relationships between family members–who like to assume that cousin marriage being illegal in some places is enough of a reason to ban it everywhere.

The fact is, there are a number of reasons why cousin marriage might be illegal in some places that ultimately doesn’t serve as a legitimate argument to ban it altogether.

More often that not, the people that like using this reasoning are people who are choosing the easiest and most self-serving interpretation of this inconsistency in the law. They are choosing what makes sense to them according to their prejudices and fears and dislikes, rather than actually asking a genuine question.

This aspect of the debate goes beyond my personal interest area and intentions for research. But I would like to share some theories (based on bits and pieces I’ve read on this topic) about why I think cousin marriage is illegal in some places. These are just theories and educated guesses, but anyone who is really curious should consider some of these things:


Sometimes there is no logic to the decisions made in a legal system, especially in places where religion rules. Extremist religious beliefs can seep into the system and affect laws, with very little consideration for facts regarding actual risks.

Population size/endogamy

I’ve noticed when looking up cousin marriage briefly that some of the places where it is banned happen to also be sparsely populated. This makes sense from a scientific perspective, since a smaller population would mean less diversity in genes, which means that the risks would be higher for consanguineous marriage–even more so if it occurs several generations in succession.

Another thing that supports this theory is that cousin marriage is often legal in bigger cities. (larger population= more genetic diversity… which means lower risks). Also, with so many people to choose from, fewer people would consider marrying a cousin, which further lowers risks to population health.

Arranged/forced marriage

When looking up something I heard about cousin marriage being illegal in a European country, I came across some legal materials that stated that “arranged” marriage specifically was illegal. Cousin marriages based on cultural traditions are often arranged. This law wasn’t a total ban…rather it was a ban on forced marriage specifically. If two cousins wanted to be married, they’d have to sign a document confirming that they are both mutually consenting to a marriage before they are allowed to marry.

So what appeared to be a total ban was really only a ban on arranged marriage. It was just something in place to protect people from being forced into a marriage they didn’t want.

 Cultural traditions

Another reason why marriage between cousins is illegal in some places may have to do with discouraging generational inbreeding. This most often seems to occur in cultures where it is a custom to marry a cousin.

If you look up the history of marriage bans in a given location, you’ll see that some of these bans occurred as a direct reaction to the problem of generational inbreeding among ethnic groups… marriage bans meant these traditions could not be continued. This also meant no more arranged marriages.

Often these same places that have bans on marriage will not prosecute two cousins living together and having kids. So the real purpose of the ban is more about discouraging multiple-generation arranged marriages– It’s not a reflection of the risks for a single generation.


Regardless of where it is banned and why, the facts still remain. First cousin marriage is legal in many places, and that is because the reproductive risks for a single generation are low. As long as it is mutually consensual, no one is abused.

The problems in cousin marriage arise when it occurs with no limits. But the solution to that should not be worldwide bans. It should be a solution that offers balance, between allowing consenting adults to be together and at the same time making sure inbreeding always remains within levels that are safe.

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