[fouc]

>Third-degree relatives (such as half-aunt, half-nephew, first cousin) on average share 12.5% genes, and sexual relations between them are viewed differently in various cultures, from being discouraged to being socially acceptable.

Relationships between cousins isn't always considered to be incest. It's more recent in the last 50-60 years, especially in USA, that cousin marriage is frowned upon based on misunderstanding the risk.

[Veen]

But is that risk not increased when the family has practiced cousin marriage for many generations?

[gadders]

It's not legally incest, but it's not a good idea.