Smaller dogs tend to have been breed for their looks, not their ability to do a task, like herd or fetch and assist in hunting. Larger dog breeds were bred for these skills. Some smaller dogs, like some terriers, were bred for hunting smaller prey, like rats. They were bred for their tenacity. Of course, I am generalising here. I’m sure people have owned small dogs that were very clever and I have certainly known large dogs that were dumb as bricks. I have known of Afghan hounds to be rather stupid and had poor sense of direction and get lost very easily. But when I see an annoying barking small dog, my son and I look at eachother and say, ‘Little dog, Little brain.’ and laugh.