Fascinating. You'll often see arguments that women are biologically hardwired to seek out single stable mates, because they need loyal resource providers to keep them protected and fed while they raise kids. Men, conversely, are hardwired to try to spread their seed around but to jealously guard their own mates, to guarantee paternity. These evolutionary arguments are used to advance the notion that single-man-single-woman marriage is 'natural', part of our biological predisposition, and that women desire single powerful men while men desire many attractive women.
The cultures of the ancient Amazon defy these claims. Polyandry was the norm, with each wife having multiple husbands and the children being raised collectively. Each child, of course, still only had one male and female parent, but the society didn't think so; they believed in partible paternity, where the child developed from the accretion of multiple fathers' sperm.
Even on the biological level this setup is viable - sperm competition will produce healthier offspring (one of the main drivers behind female promiscuity in most species.)
This social setup seemed to work well with their harsh warrior culture. Women and men alike benefited: women had replacements to step up if a given husband died, and the men built solidarity and friendships over shared wives. Children had a whole network of dads to support them into adulthood. The sex was also probably pretty wild.
Alien to us, but illuminating (to me) as an SF writer - it shows how cultures might develop differently.
