Note that this is not my post but was an unreg user's who posted it in unsuitable forum topic and so was moved here.
"1)The Predators are visiting the Earth and taught us how to build the pyramids and stuff (AVP Franchise)
2)The Engineers were also visiting the Earth (Prometheus)
3)At some point the Engineers and the Predators clashed (war is what we like so we will take it in that way). There are references of Engineers mask in Predator’s trophy collection.
4)The Predators gained upper hand in the Star systems nearer to Earth that has life. Or their Prime Planet might be very near to Earth and they can quickly project their supremacy on Earth than Engineers.
5)The Engineers studied the Predator DNAs and other sentient species DNAs and developed the Aliens to counter the Predators.
6)The Engineers predicted that the predators might take advantage of Human DNA which is same as Engineers DNA and might use it against them.
So the Engineers Strategically wanted to depopulate the Earth (Exterminate the Humans) and replace it with Aliens so that the predators will be having tough time with Aliens.
7)But the Engineers at that time seem to be having no control of any form on the aliens and it was an experiment gone out of hands and that is how alien is unleashed.
8)Predators also don’t want to destroy the Earth as they might need Humans as a way to study and gain upper hand over Engineers. Predators will always try to make us evolve more to reach as much near to Engineer’s standards to make a better game for predators.
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