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No formal studies to share.
I know a lot of poly folk in N-way relationships who seem reasonably happy about it and would likely be less happy in monogamous relationships; I know a lot of monogamous folks in 2-way relationships who seem reasonably happy about it and would likely be less happy in polygamous relationships; I know a fair number of folks in 2-way relationships who would likely be happier in polygamous relationships; I know a larger number of folks who have tried polygamous relationships and decided it wasn't for them. Mostly my conclusion from all this is that different people have different preferences.
As to whether those differing preferences are the result of genetic variation, gestational differences, early childhood experiences, lifestyle choices made as adolescents and adults, something else entirely, or some combination thereof... I haven't a clue.
I don't see where it matters much for practical purposes.
I mean, I recognize that there's a social convention that we're not permitted to condemn people for characteristics they were "born with," but that mostly seems irrelevant to me, since I see no reason to condemn people for preferring poly relationships regardless of whether they were born that way, acquired it as learned behavior, or (as seems likeliest) some combination.