If you haven't seen Prometheus, you probably don't want to read this, but honestly, I'm just going to be talking about the black goo, and not much about the plot of the movie itself.
In the beginning....Black goo is ingested by an "Engineer", he gets hella sick, disintegrates into the water and his DNA helps to create Humans as we know them to be. The reason I think he had a bad reaction to the goo is due to the Oxygen or something else in Earth's atmosphere.
Then the black goo is found on the planet. Personally, I think it's the same planet as Alien. It was big ass planet.
Anyway...the black goo hits a worm, turns it into a facehugger jr. Not quite right. So Robot infects Human with black goo. He impregnates his chick, she breeds a facehugger sr. but...still not quite right.
Facehugger Sr, facehugs an "Engineer" creates an almost Alien, alien. But it's still not quite right. At least to me it looked like a prototype version of the Alien, alien.
So here's what I think happened after:
Almost Alien, alien laid some eggs in one of those other ships nearby. However, there's no one there to fertilize them.
But when Ripley and the others get to the planet....
The eggs are fertilized with Human DNA again. Facehugger the third comes out. Perfect! Facehugger the third facehugs a Human to create the perfect Alien, alien.
So, I think it needed female and male DNA to evolve into the perfect Alien or simply two different DNA hosts-one original "Engineer" and it's evolved offspring a Human. They didn't show any female "Engineers" so unless the black goo created them too, I'm sure there has to be some, somewhere, since they were all dead when the Humans got there.
I know, it's way out there, but I've been thinking about it for a while and I just had to put it down. :-)