19 doctor. You might think that imagining a future haircut would be pretty dull. Not at all. Here is what one of my participants pictured: "I was getting my hair cut to donate to Locks of Love [a charity that fashions wigs for young cancer patients]. It had taken me years to grow it out, and my friends were all there to help celebrate. We went to my favorite hair place in Brooklyn and then went to lunch at our favorite restaurant." I asked another participant to imagine a plane ride. "I imagined the takeoff — my favorite! — and then the eight-hour-long nap in between and then finally landing in Krakow and clapping for the pilot for providing the safe voyage," she responded. No tarmac delays, no screaming babies. The world, only a year or two into the future, was a wonderful place to live in. If all our participants insisted on thinking positively when it came to what lay in store for them personally, what does that tell us about how our brains are wired? Is the human tendency for optimism a consequence of the architecture of our brains? The Human Time Machine To think positively about our prospects, we must first be able to imagine ourselves in the future. Optimism starts with what may be the most extraordinary of human talents: mental time travel, the ability to move back and forth through time and space in one's mind. Although most of us take this ability for granted, our capacity to envision a different time and place is in fact critical to our survival. It is easy to see why cognitive time travel was naturally selected for over the course of evolution. It allows us to plan ahead, to save food and resources for times of scarcity and to endure hard work in anticipation of a future reward. It also lets us forecast how our current behavior may influence future generations. If we were not able to picture the world in a hundred years or more, would we be concerned HOUSE_OVERSIGHT_030286