Harvard psychologist and researcher Daniel Gilbert opens his best-selling book Stumbling on Happiness with what he calls "The Sentence." "The Sentence" begins with these eight words: "The human is the only animal that …." Gilbert argues that every professor needs to finish that sentence.

How did Gilbert finish The Sentence? What is the defining feature of our humanity? Gilbert is a secular psychologist, but his answer is insightful. He said,

The human being is the only animal that thinks about the future …. [Human beings] think about the future in a way that no other animal can, does, or ever has, and this simple … ordinary act is the defining feature of our humanity.

The average adult spends 12 percent of the day thinking about the future, roughly one of every eight hours. We can imagine events years into the future …. If more than several minutes are involved, no animal can keep up with us.