-The Scientific Theory-
I have seen in some genealogy researches that Pacific Islanders seem to be a population that migrated from southern borders of Asia towards the Pacific Ocean. Logically people in that migrating group settled in each point of their travel from South Asia to the group of Pacific Islands.
A good way to track these journeys is to look at a world map and Google images of native people from countries between South Asia (preferably Taiwan) and the Pacific Islands. You will notice similarities in features and culture, I have done this search so I know its easy to spot.
Also within these researches, they have proven this migration theory by matching blood results throughout the Pacific and Asia. Hopefully the next person to post an answer can explain this in more detail.
Being a pacific islander myself, I have been told of stories of pacific islanders origin is that the god Tangaroa (Tagaloa, Tangaloa, Kanaloa, Ta'aroa, Tana'oa created us to live on this world (kind of replica story to God creating man). Although in the NZ Maori beliefs that Tangaroa was the son of Papatuanuku and Ranginui who created life, in the Pacific there was only one god, Tangaroa who was mainly affiliated with the sea rather than the heavens. From my rusty knowledge Tangaroa created the heavens and the earth, then created the tangata (man), and the tangata communicate with Tangaroa through the sea. Pasific Islanders who die become spirits that travel to Avaiki (Heavens) where they rest in piece and watch over the pacific island people.
Every island has a different view on purpose of the god Tangaroa, but they all believed in the one god.