I really doubt the traditional nuclear family is natural and hence "optimal" although I guess that depends on your goal. I think as an extension or outcome, perhaps the purpose of civilization, nuclear families provide safety and security rather than producing the best offspring for the species as a whole. What's better, people of every level of fitness and intelligence pairing off to produce God knows what sort of mutants that will be protected on some level by society, or a handful of males who are naturally predisposed to good health, fitness, and intelligence, turbo Chads if you will, seeding large groups of females.

I'm not saying one is better for than the other overall, but one is surely better than the other for certain outcomes. Do we want an equitable society where low status individuals, but particularly males, have a better shot at reproduction and may contribute more to building a society that propagates that "culture" of safety and equity? Or do we go with what is probably more natural? I mean i can guess why and how religions of old and civilizations formed and why they were patriarchal