danathecount t1_j9updiv wrote

There is actually research on this topic, as this problem applies to colonizing space.

Apparently, you only need a starting population of 160 people to have enough genetic diversity for a healthy population, but that's in a vacuum (no pun intended). I'm sure it would be a lower number if every so often new genetics are introduced to the population - which is probably the case on Tangier Island.

On a side note, Iceland has an app where you can make sure the person you want to be with isn't related to you.