Regarding: But what date do you put on the origin of this mythology according to science?
Tough question Mate, as the main characters in myths are usually gods, supernatural heroes and humans like the current head guy in North Korea - a propaganda creation.
Recorded or written history only goes back about 6,000 years, before that history was oral tradition/lore.
We once only had oral law, I guess our cousins the chimps still have this - oral screeching I guess you would call it.
The mythology we know today is most likely lost in antiquity, probably a good project for a budding anthropologist.
