dekadentdave said:
This would be more like The Thing where an alien micro-organism invades a host body and absorbs its genetic traits and imitates them by taking over their bodies. The Aliens obviously have an exoskeletal genetic structure including an elongated cranial structure and tail. They obviously must adapt and evolve to the host body during incubation which is why the "dog alien" in Alien3 was smaller and was a quadroped unlike most of the humanoid bipedal aliens. The Aliens genetic composition is adaptable to survival in almost any climate which is why it is one of the most adaptable species in the known universe and why the Company wants it for bio-weapons research. As Ash pointed out in his analysis that it has the ability to shed its cells and turn them into a silicon base that has the ability to be impervious to the most inhospitable environments that makes it a tough little S.O.B.
But think about it: if a queen was incubated in a dog, would it share the dog's traits? And would she pass those down to the next generation of warriors/drones? And if then one of those came upon a new species, what then? Would it continue to mutate? How long before you start losing limbs? Or the tail? Even the cranium has changed shape and size...
Now, talking about the derelict's cargo...
Were the eggs really the cargo? Or did they suffer an infestation that destroyed the crew (turned into eggs)? If so, where were the warriors? Were was the queen? And if those eggs had space jockey DNA, did it get recombined with human DNA?
(As side note, Giger envisioned the original alien as a bastardization of the human form, hence the overall human shape and the skull under the dome. And then the quadruped stance of the Fiorina alien (as a bastardization of the dog shape). I think the later designs of the alien have lost a bit of the idea, turning them into "simple" monsters.)
Back on topic:
If the derelict was a cargo ship, and the space jockey its only fatality, we could assume the eggs were a "pure" strain.
If not, I think (this was a theory put forward by someone at the gamegossip forums a long time ago) the aliens acquire traits of their hosts only in the first generation, i.e. the queen would not acquire any traits from its host, thus ensuring the eggs are "pure" alien DNA.