The usual approach to studying cognition in evolutionary psychology is in terms of information-processing mechanisms selected to solve domain-specific problems. But there are also important selective forces operating widely across domains, leading to common design features in many cognitive systems. In particular, the costs of gathering information, and of using too much information, can be reduced by decision mechanisms that rely on very limited information—or even a lack of information—to come to their choices. The pressures to use small amounts of appropriate information may also have produced particular patterns of forgetting in long-term memory and particular limits of capacity in short-term memory. Finally, selection for being able to think about past sets of events can help explain why different representations of the same information, for instance samples versus probabilities, can produce widely varying responses from people. Thus, an evolutionary perspective that takes into account environmental considerations can not only uncover domain-specific cognitive mechanisms, but also shed new light on topics of central interest to traditional cognitive psychologists, including decision making, memory, and representations of information.