When two groups decide to unify their practical affairs they also unify their cultural symbols, but do so not in a way that produces hybrid symbols but rather in a realist way that validates the existence of the symbols as discrete entities, as parts of the cosmos. [Example. Imagine one group’s symbol is a hunter, while a different group’s symbol is a bear. A merger of the symbols as symbols might result in something like a bear who is also a hunter. A combination which treats the symbols as more real than what they symbolize might yield a hunter who is wrestling with a bear, or a bear who has eaten the hunter, or a hunter who wears the defeated bear as a pelt.]
Where the eclipse of one elite by another is decisive and permanent, the mythologies are likely to be made successive; one family of gods rules over one age of the world, but that age ended, their power eclipsed; now the new gods rule. Where the eclipse is less total, there may be filiation; a more important or authoritative generation gives birth to a a generation of petty deities, or else a generation of children who overthrow their divine forebears without killing or expelling them. In parallel unifications, different gods become brothers, or spouses; or else adjacent mythical realms are introduced, so that both myth-cycles can unfurl without too much interference.