writing this because I'm bored and I doubt anyone will read this, (hopefully someone from the hive would or maybe even the fa pred group) but i just feel like saying what my theory is on how these 3 species are connected as well as their connections to the deacon (the xeno like creature at the end of prometheus). Starting with the Engineers and the Xenomorphs, in my personal opinion I don't think the Engineers made the Xenomorphs, instead they found them and attempted to use them. Instead of making new species the Engineers would of "edited" for a lack of a better word current species, my evidence for this lies in the relationship between Engineers and Humans, both sharing the same DNA patterns but having completely different phenotypes, at the start of the movie prometheus an engineer ingests some unknown liquid which unassembles his DNA back to single cell organisms. Now considering the high adaptability cappabilities of a Xeno it would be safe to assume their progression from a single cell to multi cellular organism was much faster then most life forms hence why the black liquid, which most likely was the results of harvested Xeno DNA, became organisms similar to Xenos in appearance so fast but not Xenos. Therefore the Engineers didn't create xenomorphs but instead made a species similar to them. Tampering with Xeno DNA could of also been the reason for the race's downfall and in a last ditch attempt to get rid of what they had they sent a few ships with lone pilots out to dispose of the eggs like the one found in the first alien movie. I also believe that the Yautja were enemies with the Engineers, this could explain why the Yautja have an obsession with hunting human. The Yautja could see humans as the remnants of the Engineers and therefore hunts humans as such. All three have attempted to use Xenomorps for their own purposes, Yautja for prey, Humans for weapons and pets, and Engineers unknown maybe weapons. This theory allows for all species to be both separate but connected, and allows for all franchises to be interchangeable.