High in the mountains of North Wales in a place called Llanymawddwy, lives a shepherd named John Jones with his wife Mari and his black and white dog Mack. I stood one misty summer morning in the window of their farmhouse watching John on horseback herding the sheep with Mack. A few cows were quietly chewing their cud in a nearby corner while perhaps a hundred sheep moved across the dewy meadow toward the pens where they were to be dipped. Mack, a champion Scottish collie, was in his glory. He came from a long line of working dogs, and he had sheep in his blood. This was what he was made for, this was what he had been trained to do. And it was a marvelous thing to see him circling to the right, circling to the left, barking, crouching, racing along, herding a stray sheep here, nippin…