Some Dog breeds will eventually become to twisted because they focus on one specific trait tot he determent of others they end up heavily inbreeding these poor critters...
Look at how mangled the English bulldog is, they have to breed them artificially and they look almost nothing like the original breed...
My peeve about breeders is that they can't possibly, under any circumstances, select for every adaptive quality that an animal needs. And if they're selecting for just a relative handful of traits they're going to end up with those traits, in an exaggerated sense, while completely leaving out the many traits the animal needs for its health and survival.