See my other comment in this thread about anthropologists dichotomizing societies based on nuclear vs extended families. In short, it’s orthogonal to the issue.

The issue is that across the movement of time and generations a "nuclear family" unit of parents and their offspring has all the stability and longevity of a pencil balanced on it's tip .. the clock is ticking on Hapsberg lips and the oddities of pharoahs.

Long lasting societies have a larger formal weave based on outworking and out breeding, formally moieties in the indigenous peoples of North America, Australia, Indonesia and elsewhere.

A single family unit alone is insufficient and historically cycles members in and out over half a generation through marriage and fortune seeking.

I've seen your other comments and they have that kind of first order depth expected of a simple thought and looking things up quickly on a phone.

Here's a very shallow introduction to a family of systems with many variations that lasted some 70 thousand years keeping bloodlines clean: https://en.wikipedia.org/wiki/Moiety_(kinship)