I've just finished reading Paul Robichaud's excellent work, Pan: The Great God’s Modern Return, and it's left me with a great many impressions. Not least: I would dearly love to read an autobiographical account of the pastoral protector; something along the lines of “I, Pan: The true story of a much-misunderstood, maligned, and neglected elder god” (or daemon).
On a more serious note, however:
I gather that the Arcadians, from the Peloponnese region of Greece, were an ancient and simple rustic people; indeed, according to the concept of proselenos, they were said to be older than the Moon, Selene, herself. Hence, by implication, pre-dating the Olympian gods of the Greek classical era.
In his address “On Pan’s Iconography and the Cult in the Sanctuary of Pan on the Slopes of Mount Lykaion”, in which Ulrich Hübinger reports on archaeological discoveries in Arcadia, he asks (given that the first written mentions of the god Pan only begin to appear in the fifth century BCE):
“Does Pan’s strange goatish appearance on Attic vases from Late Archaic and Early Classical times reflect earlier iconographical traditions from Arcadia? Did the ancients picture him in the beginning simply as a goat, which revealed its divine status by walking on its hind legs like a human being? Are connections even to be suspected with animal worship in the Mycenaean age?”
This was the very question I had been asking myself (albeit with scant knowledge or reading of the field, and quite without evidence).