Kluge: The Haphazard Construction of the Human Mind (Houghton Mifflin; 2008)

In a species less driven by contextual memory and spontaneous priming, I doubt that sign would have any impact. But in a species like ours, there's reason to worry. To seek a divorce is, of course, to make one of the most difficult choices a human being can make. One must weigh hopes for the future against fears of loneliness, regret, financial implications, and (especially) concerns about children. Few

*The future of advertising on the Internet is no doubt going to revolve around personalized framing. For example, some people tend to focus on achieving ideals (what is known in the literature as having a "promotion focus") while others tend toward a "prevention focus," aimed at avoiding failure. People with promotion focus may be more responsive to appeals pitched in terms of a given product's advantages, while people with a prevention focus may be more responsive to pitches emphasizing the cost of making do without the product.

people make such decisions lightly. In a rational world, a titillating billboard wouldn't make a dime's difference. In the real world of flesh-and-blood human beings governed by klugey brains, people who weren't otherwise thinking of divorce might well be induced to start. What's more, the billboard might frame how people think about divorce, leading them to evaluate their marriage not in terms of companionship, family, and financial security, but whether it includes enough ripped bodices and steamy sexual encounters.

If this seems speculative, that's because the law firm took the sign down, under pressure, after just a couple of weeks, so there's no direct evidence. But a growing literature of real-world marketing studies backs me up. One study, for example, asked people how likely they were to buy a car in the next six months. People who were asked whether they'd buy a car were almost twice as likely to actually do so than those who weren't asked. (Small wonder that many car dealers ask not whether you are going to buy a car but when.) The parallel to a lawyer's leading question is exact, the mechanism the same. Just as context influences belief by jostling the current contents of our thoughts, it also affects choice.

The cluster of phenomena I've just discussed — framing, anchoring, susceptibility to advertising, and the like — is only part of the puzzle; our choices are also contaminated by memories retrieved from within. Consider, for example, a study that examined how office workers, some feeling hungry, some not, would select which snack they'd like to have a week hence, in the late afternoon. Seventy-two percent of those who were hungry at the time of the decision (several days before they would be having the snack in question) chose unhealthful snacks, like potato chips or candy bars. Among the people who weren't feeling hungry, only 42 percent chose the same unhealthful snacks; most instead committed themselves to apples and bananas. Everybody knows an apple is a better choice (consistent with our long-term goal of staying healthy), but when we feel hungry, memories of the joys of salt and refined sugar win out.

All of this is, of course, a function of evolution. Rationality, pretty much by definition, demands a thorough and judicious balancing of evidence, but the circuitry of mammalian memory simply isn't attuned to that purpose. The speed and context-sensitivity of memory no doubt helped our ancestors, who had to make snap decisions in a challenging environment. But in modern times, this former asset has become a liability. When context tells us one thing, but rationality another, rationality often loses.

Evolutionary inertia made a third significant contribution to the occasional irrationality of modern humans by calibrating us to expect a degree of uncertainty that is largely (and mercifully) absent in contemporary life. Until very recently, our ancestors could not count on the success of next year's harvest, and a bird in hand was certainly better than two, or even three, in the bush. Absent refrigerators, preservatives, and grocery stores, mere survival was far less assured than it is today — in the immortal words of Thomas Hobbes, life was "nasty, brutish, and short."