This post is pure speculation, so with that being said is it too outlandish to speculate that the Engineers and Yautja may have crossed paths at one point? Physiologically, Humans, Yautja and Engineers share a plethora of similarities. All three are bi-peds which is uncommon among species. Even human-spawned drones utilize all fours even though they are capable of walking on two legs. Also, The muscle structure of Humans, Engineers and Yautja is extreamily similar (the relation btween Humans and Engineers is obvious becouse they created us). All share identical torso muscles, ten fingers and opposable thumbs. They are capable of abstract thought as well as emotion and reasoning, meaning they have a developed cerebral cortex(or something resembling it). Technologically, Humans mimic both Yautja and Engineer(all three use metal ships and weapons). They also all use head protection, meaning that they acknowledge the importance of their most vulnerable/important feature. Could it be possible that the Engineers influenced the evolution of the Yautja? Maybe they created them? Or perhaps they gained Engineer technology simalerly to the way Humans gained Yautja technology. Again this is just food for thought, but I wanted to get other peoples opinions on this.