This is really a good question. While it might be tempting to say this is an irrelevent line of speculation (in the same vein as "how many angels can dance on the head of a pin?"), given the acceleration technology is taking in our day, it may become very relevent, very soon.
Here are some considerations that came to mind right away...
1) We already have people begotten by natural generation, who are genetically abnormal (people with down's syndrome, for example.) Given that it is genes which biologically separate us from "animals", a strictly genetic argument could also say that these people are also not truly "human" either.
2) We are fast approaching the day (and perhaps have already arrived at it, since scientists are already doing this with animals and plants) where it will be possible to insert the genetic qualities of animals into humans. From the time in high school, I spoke of the horrifying possibility of the military sponsoring the invention of "monkey-men"... perhaps sticking gorilla DNA into a human embryo, so that it will have a human mind, but the strength and agility of donkey-kong. I was often laughed at for suggesting something like this, but now I think it's a very real possibility. Even if we don't see something as controversial as this in the near future, how about more subtle alterations of man's genetic make-up (for example, giving a man the eyes of an eagle, so he can see incredibly long distances)? Does he cease to be human? Would these hypothetical "monkey-men" be humans with souls? (right away I see horrible possibilities for skirting human rights norms were such an unfortunate breed to be created by Godless scientists.)
3) One possible resolution can be found in the scholastic/thomist idea of the human soul being the "substance" of a man (which from their p.o.v., explains why when the soul departs at death, the physical integrity of the body immediatly begins to deteriorate into simpler elements.) If we were to create an android (or some kind of genetic concoction) which manifested the qualities of a rational soul, would it not be fair to say that it actually has to have one? Would it not be the case of simply calling a spade a spade? In the same way, we can say of severely retarded children, "we know they have a soul" (based on their being begotten of human parents, and their lack of ability to manifest the qualities of humanity, says nothing of their lacking the potential to do such - that is to say, they have a soul, but because of their infirmity it has no opportunity to exercise it's powers.)
In connection with the notion of calling "a spade a spade", I think Justin brings up a valuable point, one that has been born out by modern medical meddling. Though sexual commerce is the ordinary means that men reproduce, the Fathers seem to indicate this is not how it had to be, or how it would have been had our first parents not fallen from grace. We see this ordinary rule violated all the time in modern medicine. It is entirely possible, to remove a sperm sample from a man, remove an egg from a woman, and combine the two in a laboratory (and soon, it may be entirely possible to not even have to place the newly conceived child into a woman's womb - there's no reason to believe an artificial womb would be impossible). Obviously, the result of such artificial means is human, no less in possession of a soul than you or I.
Given that the lack of natural generation does not equal "inhumanity", nor does some genetic abnormality or meddling, could it not be that a highly advanced android is simply an act of human procreation by another means?
Or is there in fact a clear line in the sand on this matter? Would the android then be an entirely new type of rationally souled life (perhaps like the angels, save it would also be corporeal like us)?
Quite an ethical can of worms.