" Brains are expensive, Bob. They are for humans, and they are for Pav, and they are for Quinlans. Twenty to twenty-five percent of daily calories go to keeping us cogitating. Now assume a Quinlan comes along with a smaller brain, maybe only needing fifteen percent. That Quinlan has an advantage, in reproduction, in keeping itself fed, and so on. Without any reason to privilege intelligent Quinlans, the new breed could take over within a dozen generations. Have that kind of stepwise mutation happen a few times, and the Quinlan race would be just another set of animals. "