Father's brother's daughter was most common but still only represented 38% of all cousin marriages, while 62% were with first or second cousins.

But most families had either no cousin marriages or only one, while for a few the rate was as high as 70%.

The percentage of Iranian cousin marriages increased from 34 to 44% between the 1940s and 1970s, according to one study.

Keeping property in the family is a final reason for cousin marriage.

Advice on cousin marriage in the Middle East has not always been positive, however.

The current rate of cousin marriage there is 54%, an increase of 12-18% over the previous generation.

He states that the social, cultural, and economic benefits of cousin marriage need to also be fully considered.

North Indians do not practice any cousin marriages and it is taboo for them.

They also have a marked preference for cross cousin marriages.

There were other instances of cousin marriage both up and down the family tree.