[MargaretR]

Ancient mythology, including the bible, indicates that humans are the result of genetic engineering performed on early apes, in which 'their' (what we call ETs) genes were mixed to make ours.

Since they had to be here to do that, they would either -
..have to have been here before us and evolved from some other species
..or, arrived here, choosing this planet as being 'habitable' for them.