Well, a chiuaua and a great dane can have offspring. They're the same species, just drastically different breeds. That's essentially what we have here. In that case they'd have a blend, however our setting has been decided to choose the genetics to end up with one or the other. Not common that a whole set would work like this, but possible... that and it'd be a mess to mix all those hybrids so they seem to have simply been written out of the plot.
