While reading about nuclear families on Wikipedia, I came across an interesting item about the Israeli kibbutz system which I’d never heard before:

The kibbutz experiment in Israel, at its outset, attempted to ensure that children were brought up communally, i.e. not in nuclear family units. This had the unexpected side-effect that children of the kibbutz all tended to treat each other as siblings, and not as potential partners, as they grew up. They therefore sought partners outside of the kibbutz and tended to leave to form nuclear families of their own. The kibbutz therefore failed as a social experiment in this respect because it was not self-perpetuating.

Obviously, this information is not entirely accurate, since kibbutzim still exist today, to my knowledge. Anyway, the information itself is pretty interesting, I think. I remember reading Jung where he talks about this idea of “exogamous” relationships versus “endogamous.” In exogamy, you look for sex partners outside of your socio-cultural group, and in endogamy, within. Both directions have associated cultural benefits and tendencies.