use his gift and to work regularly in this capacity, the spirit rewards him with the goods that it receives. These goods, however, are only "welcome addenda". They are not enough to enable a full-time shaman. Shamans live like any other member of the group, as a hunter or housewife. Due to the popularity of ayahuasca tourism in South America, there are practitioners in areas frequented by backpackers who make a living from leading ceremonies. Academic study [[File:Shaman.jpg|thumb|upright|Sámi noaidi with his drum]] Cognitive and evolutionary approaches There are two major frameworks among cognitive and evolutionary scientists for explaining shamanism. The first, proposed by anthropologist Michael Winkelman, is known as the "neurotheological theory". According to Winkelman, shamanism develops reliably in human societies because it provides valuable benefits to the practitioner, their group, and individual clients. In particular, the trance states induced by dancing, hallucinogens, and other triggers are hypothesized to have an "integrative" effect on cognition, allowing communication among mental systems that specialize in theory of mind, social intelligence, and natural history. With this cognitive integration, the shaman can better predict the movement of animals, resolve group conflicts, plan migrations, and provide other useful services. The neurotheological theory contrasts with the "by-product" or "subjective" model of shamanism developed by Harvard anthropologist Manvir Singh. According to Singh, shamanism is a cultural technology that adapts to (or hacks) our psychological biases to convince us that a specialist can influence important but uncontrollable outcomes. Citing work on the psychology of magic and superstition, Singh argues that humans search for ways of influencing uncertain events, such as healing illness, controlling rain, or attracting animals. As specialists compete to help their clients control these outcomes, they drive the evolution of psychologically compelling magic, producing traditions adapted to people's cognitive biases. Shamanism, Singh argues, is the culmination of this cultural evolutionary process—a psychologically appealing method for controlling uncertainty. For example, some shamanic practices exploit our intuitions about humanness: Practitioners use trance and dramatic initiations to seemingly become entities distinct from normal humans and thus more apparently capable of interacting with the invisible forces believed to oversee important outcomes. Influential cognitive and anthropological scientists such as Pascal Boyer and Nicholas Humphrey have endorsed Singh's approach, although other researchers have criticized Singh's dismissal of individual- and group-level benefits. David Lewis-Williams explains the origins of shamanic practice, and some of its precise forms, through aspects of human consciousness evinced in