Decisions can often be modeled by what I call fast and frugal heuristics. Sometimes they're faster, and sometimes they're more frugal. Deciding which of two jobs to take, for instance, may involve consequences that are incommensurate from the point of view of the person making the decision. The new job may give you more money and prestige, but it might leave your children in tears, since they don't want to move for fear that they would lose their friends. Some economists may believe that you can bring everything in the same common denominator, but others can't do this. A person could end up making a decision for one dominant reason.

We make decisions based on a bounded rationality, not the unbounded rationality of the decision maker modeled after an omniscient god. But bounded rationality is also not of one kind. There is a group of economists, for example, who look at the bounds or constraints in the environment that affect how a decision is made. This study is called "optimization under constraints," and many Nobel prizes have been awarded in this area. Using the concept of bounded rationality from this perspective you realize that an organism has neither unlimited resources nor unlimited time. So one asks, given these constraints what's the optimal solution?

There's a second group, which doesn't look at bounds in the environment but at bounds in the mind. These include many psychologists and behavioral economists who find that people often take in only limited information, and sometimes make decisions based on just one or two criteria. But these colleagues don't analyze the environmental influences on the task. They think that for a priori reasons people make bad choices because of a bias, an error, or a fallacy. They look at constraints in the mind.

Neither of these concepts takes advantage of what the human mind takes advantage of: that the bounds in the mind are not unrelated to the bounds in the environment. The bounds get together. Herbert Simon developed a wonderful analogy based on a pair of scissors, where one blade is cognition and the other is the structure of the environment, or the task. You only understand how human behavior functions if you look at both sides.

Evolutionary thinking gives us a useful framework for asking some interesting questions that are not often posed. For instance, when I look at a certain heuristic — like when people make a decision based on one good reason while ignoring all others — I must ask in what environmental structures that heuristic works, and where it does not work. This is a question about ecological rationale, about the adaptation of heuristics, and it is very different from what we see in the study of cognitive illusions in social psychology and of judgment decision-making, where any kind of behavior that suggests that people ignore information, or just use one or two pieces of information, is coded as a bias. That approach is non-ecological; that is, it doesn't relate the mind to its environment.

An important future direction in cognitive science is to understand that human minds are embedded in an environment. This is not the usual way that many psychologists, and of course many economists, think about it. There are many psychological theories about what's in the mind, and there may be all kinds of computations and motives in the mind, but there's very little ecological thinking about what certain cognitive strategies or emotions do for us, and what problems they solve. One of the visions I have is to understand not only how cognitive heuristics work, and in which environments it is smart to use them, but also what role emotions play in our judgment. We have gone through a kind of liberation in the last years. There are many books, by Antonio Damasio and others, that make a general claim that emotions are important for cognitive functions, and are not just there to interrupt, distract, or mislead you. Actually, emotions can do certain things that cognitive strategies can't do, but we have very little understanding of exactly how that works.

To give a simple example, imagine Homo economicus in mate search, trying to find a woman to marry. According to standard theory Homo economicus would have to find out all the possible options and all the possible consequences of marrying each one of them. He would also look at the probabilities of various consequences of marrying each of them — whether the woman would still talk to him after they're married, whether she'd take care of their children, whatever is important to him — and the utilities of each of these. Homo economicus would have to do tons of research to avoid just coming up with subjective probabilities, and after many years of research he'd probably find out that his final choice had already married another person who didn't do these computations, and actually just fell in love with her.