Surf to the course descriptions at your favorite university's classics or religion departments, say classics at Harvard , and look for courses comparing and contrasting Christianity to Ancient Pagan religions. You won't find any. Christianity compared to Judaism, Islam, Hinduism, Buddhism, yes. Christianity compared to Paganism, nothing. It's as if a thousand years of western religious history never happened.
History is written by the victors.
In the first centuries AD Paganism and Christianity were in competition. The Christians won. The history you know was written by them. Christianity was miraculous and discontinuous. It didn't evolve, it was created a new species whole and unique.