Reasoning, defined as the production and evaluation of reasons, is a central process in science. The dominant view of reasoning, both in the psychology of reasoning and in the psychology of science, is of a mechanism with an asocial function: bettering the beliefs of the lone reasoner. Many observations, however, are difficult to reconcile with this view of reasoning; in particular, reasoning systematically searches for reasons that support the reasoner’s initial beliefs, and it only evaluates these reasons cursorily. By contrast, (...) reasoners are well able to evaluate others’ reasons: accepting strong arguments and rejecting weak ones. The argumentative theory of reasoning accounts for these traits of reasoning by postulating that the evolved function of reasoning is to argue: to find arguments to convince others and to change one’s mind when confronted with good arguments. Scientific reasoning, however, is often described as being at odds with such an argumentative mechanisms: scientists are supposed to reason objectively on their own, and to be pigheaded when their theories are challenged, even by good arguments. In this article, we review evidence showing that scientists, when reasoning, are subject to the same biases as are lay people while being able to change their mind when confronted with good arguments. We conclude that the argumentative theory of reasoning explains well key features of scientists’ reasoning and that differences in the way scientists and laypeople reason result from the institutional framework of science. (shrink)

Religious healing specialists such as shamans often use magic. Evolutionary theories that seek to explain why laypersons find these specialists convincing focus on the origins of magical cognition and belief in the supernatural. In two studies, we reframe the problem by investigating relationships among ethnomedical specialists, who possess extensive theories of disease that can often appear “supernatural,” and religious healing specialists. In study 1, we coded and analyzed cross-cultural descriptions of ethnomedical specialists in 47 cultures, finding 24% were also religious (...) leaders and 74% used supernatural theories of disease. We identified correlates of the use of supernatural concepts among ethnomedical specialists; incentives and disincentives to patronize ethnomedical specialists; and distinct clusters of ethnomedical specialists that we label prestigious teachers, feared diviners, and efficacious healers. In study 2, we interviewed 84 Maasai pastoralists and their traditional religious and non-religious healing specialists. We found that laypersons relied on medicinal services based on combinations of efficacy, religious identity, and interpersonal trust. Further, laypersons and specialists largely used abstract concepts that were not conspicuously supernatural to describe how local medicines work. We conclude that religious healers in traditional societies often fulfill a practical and specialized service to local clients, and argue that supernatural theories of disease often reflect abstract cognition about rare phenomena whose causes are unobservable (e.g., infection, mental illness) instead of a separate “religious” style of thinking. (shrink)