suppose;

an advanced race of beings (let's call them elo's) arrive on earth looking for raw materials. mainly gold, to use as radiation shielding on their spaceships. instead of doing the digging themselves, they look for an animal that can to do the job for them. maybe something like an ape would be an ideal candidate, an animal that had already evolved an opposing digit, and could fetch and carry with some dexterity. now, i'd imagine that even the most advanced ape, as we know them, would still have some trouble being a miner or whatever, so there would need to be a little genetic engineering involved to get the workers just right. make them a bit smarter so as to be easier organised. after many failed experiments, the elo's finally find a way to create the workers (let's call them the uz) that they need by augmenting ape dna with 'smart' code from their own.

as well as educating the uz in basic hexidecimal mathematics, written language, justice (the elo's being a very just race, of course. well..., at least in their own eyes), farming, animal husbandry etc, they also told them about where everyone came from. the elo's explained that their home planet ( X ) is part of this solar system, trapped like many of our comets in a huge retrograde orbit, 30 degrees off the eliptical. they also explained how they had created the uz, but the uz , even though smarter than the average bear, had difficulty in comprehending the technical details. (this would lead to much confusion later)

anyway, planet X had rounded the sun already, and was about to begin it's 7000 year voyage through the darkness again, so the elo's got their s**t together and headed home. the economy that they had created for the uz, based on gold, would ensure that there was plenty of it stockpiled for their return.

that was almost 7000 years ago.