Is it legal and morally acceptable to marry your cousin? The answer varies depending upon your definition of the word "cousin," your location, and your personal or cultural beliefs.

What Is a Cousin? Your cousins are family members who you share a relative that is at least one generations away. Your parents' siblings' children are your first cousins and your parents' first cousins are your second cousins.

What Is a Cousin?

There are many degrees and types of cousins. While first cousins are close relatives, second and third cousins are not. Here are a few definitions:

a first cousin: the child of your aunt or uncle (your parent's sibling's child) is your first cousin

a second cousin: the child of your parent's cousin is your second cousin

a cousin once (or twice) removed: a cousin separated by a generation (for example, your parent's cousin is your cousin once removed)

third cousin: the children of your parent's second cousin

The chances are that you know and spend time with your first cousins. You may happen to know your second cousins. But unless you have a particularly large and close family, you may never have met third or fourth cousins or cousins who are once or twice removed.

Why Is There a Taboo Against Marrying Cousins?

In some cultures, there is a taboo against cousins marrying cousins. That taboo is rooted in rules and laws against incest, and a result of genetic concerns: people who are closely related may share genes for a variety of illnesses and developmental issues. When siblings marry one another, children are more likely to be born with those diseases or other issues.

In fact, however, while children of non-related couples have a 2-3% risk of congenital disabilities, children of first cousins have a 4-6% risk. This is not a huge increase in risk, though it is real. Thus, first cousins who marry (assuming that they are doing so legally) should certainly seek genetic counseling before having children.

But many cultures encourage marriage between cousins, for a variety of reasons. Queen Victoria, for example, married her first cousin to maintain a royal lineage and forge political alliances. Many Asian cultures encourage first cousin marriage to strengthen clan relationships.

In the United States, second cousins are legally allowed to marry in every state. What's more, the genetic risk associated with second cousins having children is almost as small as it would be between two unrelated individuals. Marriage between first cousins, however, is legal in only about half of American states.

Which States Allows First Cousin Marriages?

As you'll see, many states allow first cousin marriages only if there will be no offspring from those marriages. Others allow cousin marriages only in special circumstances. An adoptive cousin or a half-cousin may be allowed to marry.