In a case like that, we'd expect all populations of the species to eventually get longer noses, because longer noses produce a clear advantage. But what if short noses were best when living in some habitats, and longer noses were best when living in other habitats? In that case we'd expect to see those with longer noses move to the habitats where they do best, and form a population that continues to evolve longer noses. At the same time we'd expect to see the short nosed individuals to stay where short noses do best, and to form a population that maintains short noses. Eventually additional genetic differences would build up in the two populations and they'd evolve into different species. Those species might each produce new species themselves which were even more different. That's essentially what happened to the line leading to chimps and the line leading to humans from their common ancestor.
Rucha101 wrote: " Because they used it alot, their sense of smell EVOLVED and grew and grew and grew over millions of years."
The only problem here is that the described selective pressure would be to evolve a nose that is better at smelling. A longer nose is not necessarily better at smelling. Dogs have longer snouts than we do, and a better sense of smell, but their actual noses are no longer than our own.