Nat, that would be quit an interesting study. When I look at pictures of me when I was in my late teens/early twenty's, it is definatly noticable that I was much firmer. Now at the still young age of 34, I would say my breasts have dropped about an inch. Was it because I rarely wore a bra from college to just last year, or was it because of natural aging. I tend to think it was because of natural aging and the effects of gravity. Although looking at the difference between twins would be interesting.