Suppose, during a date, you casually say, “The sugar maples in Harvard Yard were so beautiful every fall term.” Here’s what you’re signaling, as translated by Dr. Miller:

“My S.A.T. scores were sufficiently high (roughly 720 out of 800) that I could get admitted, so my I.Q. is above 135, and I had sufficient conscientiousness, emotional stability and intellectual openness to pass my classes. Plus, I can recognize a tree.”

Or suppose a young man, after listening to the specifications of the newest iPhone or hearing about a BMW’s “Servotronic variable-ratio power steering,” says to himself, “Those features sound awesome.” Here’s Dr. Miller’s translation:

“Those features can be talked about in ways that will display my general intelligence to potential mates and friends, who will bow down before my godlike technopowers, which rival those of Iron Man himself.”

Most of us will insist there are other reasons for going to Harvard or buying a BMW or an iPhone  and there are, of course. The education and the products can yield many kinds of rewards. But Dr. Miller says that much of the pleasure we derive from products stems from the unconscious instinct that they will either enhance or signal our fitness by demonstrating intelligence or some of the Big Five personality traits: openness, conscientiousness, agreeableness, stability and extraversion.

In a series of experiments, Dr. Miller and other researchers found that people were more likely to expend money and effort on products and activities if they were first primed with photographs of the opposite sex or stories about dating.

After this priming, men were more willing to splurge on designer sunglasses, expensive watches and European vacations. Women became more willing to do volunteer work and perform other acts of conspicuous charity  a signal of high conscientiousness and agreeableness, like demonstrating your concern for third world farmers by spending extra for Starbucks’s “fair trade” coffee.