Confucius Say: Primogeniture is Here to Stay

I'm not necessarily agreeing with Byrne (don't know his work), but we can see the motivation for such a first-born rule. This was the means by which the primary ruling line of kings maintained control over the various priesthoods in widely distributed locales, including the Jerusalem priesthood. It was a "world-wide" family-run business, and included both aspects of Church and State!

Leading members of the royal family invariably maintained many different local identities and typically had local wives (even if local custom prohibited polygamy!). This is the complexity that we are forced to deal with, so we may as well get used to it.