Many animals are capable of learning from others, a process referred to as social learning. There is little doubt that a capacity for social learning is an adaptation and that it typically results in adaptive behavior. What is less clear is whether there are circumstances under which social learning can result in the transmission of outdated, inappropriate, or maladaptive information. Here we report an experimental study that investigated the social learning and transmission of maladaptive foraging information through small social groups of guppies, Poedtia rtticulata. This experiment used a transmission chain design in which fish in small founder groups were trained to take either an energetically costly circuitous route to a feeder or a less costly short route, with trained founder members gradually replaced by untrained conspecifics. Three days after all the founders had been removed, the behavioral traditions of groups of untrained fish were still strongly influenced by their founder's behavior. Moreover, the rate at which untrained subjects that shoaled with founder conspecifics trained to take the long route learned to take the short route was significantly slower than for fish foraging alone. The results provide unequivocal evidence that maladaptive information can be socially transmitted through animal populations and imply that socially learned information can inhibit learning of the optimal behavior pattern. There is little doubt that the ability to learn from others is an important adaptation that allows many animals to acquire information concerning foods, predators, and mates at low cost (Bateson, 1988;Giraldeau, 1997; Ploddn, 1988). By learning from others, animal* can avoid potentially hazardous learning trials and reduce time spent on exploration (Galef, 1995). There is also little doubt that social learning generates adaptive behavior (Galef, 1995), and much work in die field has been dedicated to understanding die role of social interactions in the development of patterns of behavior that enhance the fitness of free-living animals (Galef, 1996; Giraldeau, 1997). Socially learned behavior patterns may be subjected to fitness trade-offs in exactly die same manner that behavior patterns are acquired through other processes (Stephens and Krebs, 1986), but diere is no reason to believe that the behavioral expression of acquired information is less likely What is less dear is whether social learning processes in anfma1« can result in die transmission of maladaptive information through a population, that is, information, expressed in behavior, that reduces die fitness of die learner relative to an alternative behavior pattern and that leads to suboptimal behavioral traditions. That social learning processes can result in die transmission of maladaptive information is a conclusion common to several theoretical models that explore die adaptive value of learning from others (Boyd and Richerson, 1985; Feldman et al., 1996; Laland et aL, 1996). Such analyses have reached a consensus that social learning is...