igorfrankensteen wrote:when and why did large groups of people cease being satisfied with purely magical explanations of their spiritual heritage, and instead begin to call for believable physical histories instead?
It likely started when some pre-Socratic philosophers expressed skepticism about their society's theology. Xenophanes was notable for pointing the absurd anthropomorphism of its deities. Protagoras argued that nobody knows for sure what the gods are really like. Such skepticism likely set the stage for people asking what the gods were really like. If they weren't immortal people with superpowers, then what were they?
Theagenes of Rhegium - His Thoughts on Cosmology, Religion, and Myth
Theagenes (~525 BCE) proposed that deities were allegories for forces of nature, and that their fighting was allegories of conflicts and oppositions between them, like fire vs. water.
In this menagerie, fire was represented by Apollo, Helios and Hephaestus, water by Poseidon and Scamander, air by Hera, and so forth. Also abstract qualities had divine representation - wisdom with Athene, desire with Aphrodite, reason with Hermes and folly, no less, with Ares. For gods to actually do battle, in the way Homer has it, would be unbecoming to them.
Euhemerus - His Thoughts on Cosmology, Religion, and Myth
But Euhemerus (~ 330 - 260 BCE) was much more successful. He proposed that while some deities are indeed cosmic and immortal, other deities were originally human heroes. Euhemerism, as it is called, became a very popular theory.
It must be noted that despite their skepticism, philosophers like these also believed that one ought to worship these entities. Sextus Empiricus, in Arguments against Belief in a God, stated "We sceptics follow in practice the way of the world, but without holding any opinion about it. We speak of the Gods as existing and offer worship to the Gods and say that they exercise providence, but in saying this we express no belief, and avoid the rashness of the dogmatisers." (translation quoted by Bertrand Russell, A History of Western Philosophy).