Being able to "grow" a certain muscle (a muscle being a single force producing unit that contracts from origin to insertion) makes no sense at all. The body is a very efficient device and altering the proportion shape with training (by, for example, making the pectoralis major top heavy) would change the angle of pull and dramatically alter the natural biomechanical efficiency.
Also remember that these distinctions (upper, lower, and outer) have NO anatomical definition. They are what trainers will use to confuse people into thinking they have an answer to something that is probably complete bullshit. Maybe we can look further into this problem when we actually understand about the growth mechanism and it's response, but until then it simply makes more sense that you can't isolate a portion of a muscle.