March 07, 2018
Before the Industrial Revolution in the United States, Canada and Europe, you might have ended up married to a fourth cousin. People didn’t travel far to find a spouse, and the closer you were to home, the more likely it was you’d marry within your family. Then, in the late 19th century, something changed, and people stopped marrying their cousins.
Source: New York Times
https://www.nytimes.com/2018/03/01/science/cousins-marriage-family-tree.html