Doesn't sound very sacred to me.
Incest was decriminalized in Alaska between 1999 and 2006, because the Native population lobbied to have the statutes abolished. The reasoning was that the average village size in Native Alaskan villages is 60 individuals, and, especially in the even smaller villages, other than brother and sister there might not be even one other available marriage partner within 10 years of age within their community. There are 11 major Native tribes in Alaska, plus the Eskimos/Inuits. Almost all the Native tribes shun the Inuits. The tribes themselves are famous for having extremely complicated conflicts among each other. Not one tribe finds all the other tribes acceptable. One tribe is considered acceptable by every other tribe, but another tribe only finds that tribe and themselves acceptable. In most cases, other members of one's tribe will live hundreds of miles away in a land where no roads exist, and, while one's tribe may consider the nearest tribe to be acceptable for marriage, that nearest tribe may not reciprocate the feeling. So it's hard to find a life partner. That logic, while we were living there, persuaded the legislature. Sarah Palin was Governor when the incest prohibition was reinstituted. I seriously doubt, though, especially given the tremendous clout the Natives have in the state (they own most of the oil rights) that anyone from Juneau is going to mount a campaign (no pun intended) to force brothers and sisters (or sons and mothers) from becoming one flesh.
P.S. Most of the tribes do not have anything close to strict prohibitions against polygamy, either.
