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Science, Math, & Technology


Adelphogamic biandry and partible paternity

Posted 2 Weeks ago by chiarizio

I have a technical question. Maybe someone here can calculate the answer.
Imagine a society and culture where every man marries just one woman and every woman marries just two men; and her husbands are each other’s “brothers”.
The people believe in partible paternity. That is, if both husbands make love to their wife while she’s pregnant, they believe they are both equally the father of her baby.
So the two husbands have a 50% chance of being full-brothers by OUR lights; they definitely have the same mother and there’s a 50% chance they have exactly the same father.
OTOH the other 50% of the time they’ll be closer-related than just half-brothers; the father of one of them will be the “brother” of the father of the other. So they’ll be first cousins on their fathers’ sides, by OUR lights.

So they have the same mother.
There’s a 50% chance they have the same father.
There’s a 50% * 50% = 25% chance their fathers were full brothers.
There’s a 25% chance their fathers were half-brothers and first-cousins.

How do we work out how related, on average, a man is to his “brother”?

How do we work out how related, on average, a man is to his “son”?

Thanks for any help!

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