Our (nearly) cavemen-optimized brains fear our children will starve or be eaten if we don't help them. Sexual jealousy is probably genetically encoded meaning lots of men want their mates to be exclusive to them. The following is pure speculation with absolutely no evidence behind it: but I wonder if a problem with open relationships involving couples planning on having kids is that the man might (for genetic reasons) care less for a child even if he knows with certainty that the child is theirs. A gene that caused a man to care more for children whose mothers were thought to be sexually exclusive with the man might increase reproductive fitness.
I'm still unsure why I'm vehemently being downvoted for taking up this position. Perhaps it's because people confuse it for men's rights extremist thoughts? Why is the possibility being completely disregarded here that it's only memes and a small set of genetic predispositions (such as reward from helping others via empathy and strong empathy for small humans) that jumpstart decent behavior? I think I've read somewhere that kittens learn how to groom by watching other cats. If other mammals can't fully encode basic needs such as hygiene genetically, how can complex human behaviors? An important implication from this would be that culture carries much more value than we would otherwise attribute to it.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Notes for future OT posters:
1. Please add the 'open_thread' tag.
2. Check if there is an active Open Thread before posting a new one. (Immediately before; refresh the list-of-threads page before posting.)
3. Open Threads should be posted in Discussion, and not Main.
4. Open Threads should start on Monday, and end on Sunday.