My theory is that the Black liquid in the vials is actually Xenomorph DNA/Bio-matter that has been broken down by the Black liquid we see at the start of the film (how the Engineer seeds life on Earth?) and then stored in the vials, why?
1) Its easier to transport the Black Liquid rather than Eggs (proven by the crash on LV-426, later disproved by the incident on LV -223)
2) Engineers like to evolve lifeforms, so they chose to evolve the Xenomorphs into a more efficient Bio-weapon. In the classic form, the Facehugger needs a large lifeforms to reproduce, the black liquid potentially just needs any organism to make Xenos/Monsters. Imagine the effect if the liquid got into a water supply?!
1) Its easier to transport the Black Liquid rather than Eggs (proven by the crash on LV-426, later disproved by the incident on LV -223)
2) Engineers like to evolve lifeforms, so they chose to evolve the Xenomorphs into a more efficient Bio-weapon. In the classic form, the Facehugger needs a large lifeforms to reproduce, the black liquid potentially just needs any organism to make Xenos/Monsters. Imagine the effect if the liquid got into a water supply?!
3) The classic Xenomorphs need a nest and a queen (maybe?), and thus will be located in one place, making fighting back against a Xeno invasion a high possibility as they will be centred in one location per Hive. This also means Eggs will be produced in these central locations adding an extreme vulnerability to this strategy. However, using the Black Liquid, you eliminate the need for a Queen to reproduce and eliminate the need for a Hive as the reproduction cycle has been changed.
Hope you enjoy my OPINION, let me know what you guys think? :)