Are the lower limits for source population based on exclusivity (monogamy)? Because it seems like a promiscuous group is going to be viable for a much smaller population.
Correct me if I’m wrong, but there wasn’t just one “group” that peopled the new world. Navajos and other Na-Dene speakers etc. derived from a separate and much later migration event, right?
Here is a BBC documentary about cousin marriage amongst the Pakistani community in the UK and the health problems it causes.
‘should I marry my cousin’ Should I Marry My Cousin (BBC / 2017) on Vimeo
Cousin marriage is also tradition amongst Aristocracies in order to preserve a royal lineage in the days when being a member of a royal family, put on this earth to rule by divine ordinance was an important political advantage when it came to deciding who would be King.
The same idea was adopted by some of the American corporate dynasties like the DuPonts and the Rothchilds.
I guess how safe it is depends very much on what nasty recessive gene lie lurking in the family genome.
The answer to that question is nearly solved as the cost of genome sequencing becomes cheaper and we learn how to assess the risk of congenital disease between two individuals accurately. Combine that with gene editing and IVR and the future presents some interesting ethical issues.
Some of these issues were explored in the SciFi movie Gattaca.
Re Pakistani intermarriage - From what I heard on a few documentaries a while ago, cousin (well, 2nd and third especially) is what builds the clans in some middle eastern communities. There are several groups, call them clans, or extended families or tribes or whatever (all loaded words). basically, the clans are extended families which reinforce the bonds with marriages to others of the same extraction, who tend to be moderately closely related. Thus you have many comingled but not usually related groups or families in the same general area.
it was suggested too that part of the Palestinian problem was not so much political or ideological, as inter-tribal conflict for dominance between different clans, some of whom support one faction or the other; hence the fight between Wes Bank and Gaza. Until they can agree to put old rivalries aside and work together, the region will be to fractured to agree among each other, let alone talk peace with an outside group.
FWIW - More on UK Pakistani cousin marriage, published on BBC today.
The only bright spot:
*The couple’s experiences have led others in the family, including Ruba’s brother, to reject cousin marriage.
“We never use to think about the risks - up to my children we’ve never thought it was wrong to marry in the family, but because I’ve been through it my other relatives do think twice about going in the family,” Ruba says.*
The rest is just distressing.
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Another case in point.
The polygamous FLDS community in Arizona has an unusually high incidence of a very rare recessive genetic disorder called fumerase deficiency. It’s a very rare condition (only a few dozen known cases). Over half of the known cases in the world are among residents of this tightly knit and isolated community.
Probably not the best example for the general case as polygamy reduces genetic diversity more than in a group with world-views that lead to a more horizontal parentage.
One man having 55 wives and 59 children going to be a much larger choke point.
Specifically, that’s the Colorado City/Hilldale FLDS group which is one of the most inbred and cultish. Other FLDS polygamists are not nearly so genetically isolated.