Canines may not be the deepest thinkers in the world. But perhaps that's for the best. The life of a dog—sitting alone all day, waiting for everyone to come home—can be pretty boring. Super-smart animals would probably get totally stressed out, says University of Pennsylvania researcher James Serpell. Look at it this way: if dogs were any smarter, they probably wouldn't choose to hang around with us. Which best describes the tone of the passage?