It only takes one charismatic leader to do so. "Spontaneous initiation," whatever that is, is neither necessary nor sufficient.
4. How does one become a shaman?
Some have wondered if the experience of shamanic ecstasy or flight makes a person a shaman. Generally speaking, most would say no. A shaman is more than someone with an experience. First, he or she is a trained initiate. Usually years of enculturalization and training under a mentor precede becoming a functioning shaman. Second, a shaman is not just an initiate who has received inner and outer training, but is a master of shamanic journeying and techniques (shamanic ecstasy). This is not a casual acquaintance with such abilities, there is some degree of mastery of them. Finally, a shaman is a link or bridge between this world and the next. This is a sacred trust and a service to the community. Sometimes a community that a shaman serves in is rather small. In other instances it may be an entire nation. A lot of that depends on social and cultural factors.
One becomes a shaman by one of three methods:
Hereditary transmission;
Spontaneous selection or "call" or "election"
personal choice and quest. (This latter method is less frequent and traditionally such a shaman is considered less powerful than one selected by one of the two preceding methods.) The shaman is not recognized as legitimate without having undergone two types of training:
Ecstatic (dreams, trances, etc.)
Traditional ("shamanic techniques, names and functions of spirits, mythology and genealogy of the clan, secret language, etc.) The two-fold course of instruction, given by the spirits and the old master shamans is equivalent to an initiation." (Mircea Eliade, The Encyclopedia of Religion, v. 13 , p. 202; Mcmillian, N.Y., 1987.) It is also possible for the entire process to take place in the dream state or in ecstatic experience. (bold mine)
"A common experience of the call to shamanism is a psychic or spiritual crisis, which often accompanies a physical or even a medical crisis, and is cured by the shaman him or herself....The shaman is often marked by eccentric behavior such as periods of melancholy, solitude, visions, singing in his or her sleep, etc. The inability of the traditional remedies to cure the condition of the shamanic candidate and the eventual self cure by the new shaman is a significant episode in development of the shaman. The underlying significant aspect of this experience, when it is present, is the ability of the shaman to manage and resolve periods of distress." - Dean Edwards
"Frequently a candidate will gain shamanic powers during a visionary experience in which he or she undergoes some form of death or personal destruction and disintegration at the hands of divine beings, followed by a corresponding resurrection or reintegration that purges and gives a qualitatively different life to the initiate. For example, the Siberian (Tagvi Samoyed) Sereptie, in his long and arduous initiatory vision (on which see below), was at one point reduced to a skeleton and then was 'forged' with a hammer and anvil. Autdaruta, an Inuit initiate, had a vision in which he was eaten by a bear and then was vomited up, having gained power over the spirits." -James R. Davila
"...The important moments of a shamanic initiation are these five; first, torture and violent dismemberment of the body; second, scraping away of the flesh until the body is reduced to a skeleton; third, substitution of viscera and reveal of the blood; fourth, a period spent in Hell, during which the future shaman is taught by the souls of dead shamans and by 'demons'; fifth, an ascent to Heaven to obtain consecration from the God of Heaven" -Mircea Eliade
"In the ages of the rude beginnings of culture, man believed that he was discovering a second real world in dream, and here is the origin of metaphysics. Without dream, mankind would never have had occasion to invent such a division of the world. The parting of soul and body goes also with this way of interpreting dream; likewise, the idea of a soul's apparitional body: whence, all belief in ghosts, and apparently, too, in gods."
- Neitzsche,
Human, All-Too-Human