When the family tree stops branching - Cousin Marriages

I've ran across quite a few cousin marriages in my family tree.  Today's example comes from 1678 Barnstable, British Massachusetts Bay Colony when 22-year-old John Fuller married his 18 year-old first cousin once removed, Mehitable Rowley.  

Mehitable's mother, Elizabeth Fuller, and John were first cousins because their fathers were brothers.  (Sidenote: This whole bunch belongs to Mayflower passenger Edward Fuller.)

It doesn't seem too scandalous to my sensibilities since the bride and groom are close in age.  With the combination of large families living and working together and limited opportunity to meet others was a perfect storm for inter-familial marriages. 

Cousin marriage was legal everywhere in the US before the Civil War.   There was a cultural shift away from cousin marriage because such marriages were seen as a remnant of a more primitive stage of human social organization.  

Cousin marriage was practiced to keep cultural values intact, preserve family wealth, maintain geographic proximity, keep tradition, strengthen family ties, and maintain family structure.   In other words, it was seen as old fashioned.  Opinion favoring keeping the bloodline within the family gave way to the idea that variety will increase the vigor and variety of the gene pool.

Currently, 24 US states ban marriage between first cousins, 19 states allow marriages between first cousins, and seven U.S. states allow only some marriages between first cousins. In such states, marriages between cousins are allowed in a variety of circumstances such as: when the cousins are over 65; or when cousins are over 55 and at least one is infertile; or the cousins have undergone genetic screening.   

From a worldwide perspective, it appears cousin marriage is allowed more than restricted. Cousin marriage is accepted in Europe, Canada, Mexico, South America, parts of Africa, the Middle East, Japan, and Australia. 

Cousin marriage is legally prohibited in mainland China, Taiwan, North Korea, South Korea, and the Philippines.