The universal norm that reinforces some form of exogamy is known as the

This would be the incest taboo. Since exogamy is the concept of marrying outside one's own circle, the incest taboo and the general prohibition against marrying (or having relationships) within one's family or close circle helps to make sure that people propagate their genetics and characteristics as far as possible.

You don’t list any options but the one that frets overspending and the consequences of that.