Mestizo shamanism is found in an arc from southern Colombia and Ecuador to northern Bolivia, through the present-day Peruvian departamentos of Loreto and Ucayali, westward along the Río Marañon, and spilling over eastward into western Brazil. This distribution is the result of historical factors, one of which was the great Rubber Boom — a period of about thirty-five years, approximately from 1880 to 1914, which transformed Amazonian culture in ways both profound and irremediable.

There are a number of rubber-producing trees in the Amazon, but two genera are of primary importance. Hevea species produce a latex called siringa, and Castilloa species produce a latex called caucho. To understand the formation of mestizo shamanism, we have to understand the biology of these two types of rubber trees.

The latex of Hevea brasiliensis was considered the finest in the Amazon. Moreover, this latex will flow from shallow incisions in the bark, and the tree can therefore be tapped for years without serious damage. But Hevea trees have two significant disadvantages. First, although they are capable of growing in the uplands, they are found primarily in low-lying periodically flooded areas, where they can be tapped only half the year, during the dry season.

The ideal would therefore be to create upland plantations, where the trees could be readily tapped year round. But here there is a second disadvantage. Hevea trees are susceptible to a fungal disease called South American leaf blight, caused by the fungus Microcyclus ulei, native to the Amazon. The fungus is transmitted from tree to tree, and thus effectively precludes growing the trees close together on plantations. The latex must be tapped from wild trees, which grow widely separated in the jungle — about two trees per hectare.

A seringuero, a collector of siringa, therefore lived in a hut, perhaps with a small garden, and regularly followed a path — called an estrada — which he cut through the jungle to two hundred or so Hevea trees, tapping half on one day and half on the next. Seringueros were essentially tenant farmers, held in peonage by constantly increasing debt, subject to disease, harsh weather, poor diet, and insect pests. At some point, many gave up any hope of ever ending their bondage to the rubber trees. At the same time, since they were sedentary, and steady sources of high-quality latex, rubber bosses and overseers had economic motives to limit violence and abuse of their tenants.

On the other hand, caucho, the latex of Castilloa trees, was considerably less desirable. Since the trees grew above flooded areas, they could be exploited year round. But the trees could not be tapped, since incisions yield little latex. Rather, all the latex had to be gathered at once, with deep cuts in the trunk, branches, and roots, which produced a large amount of rubber, but killed the tree.

A cauchero was therefore constantly looking for more caucho trees to drain. Caucheros frequently worked in teams, since it is almost impossible to bleed a large caucho tree alone. Always on the move, they were in constant danger of becoming lost in unfamiliar jungle; they could not grow gardens, as many seringueros did, and thus became increasingly indebted for supplies whose price was set arbitrarily to maintain indebtedness; if they became sick, no one would bother to look for them, because their location at any moment was unknown.

The itinerant nature of caucho production required a permanently mobile labor force and constant territorial expansion. Rubber bosses had no incentive to create long-term commercial ties with seminomadic and fungible caucheros. The relative isolation of the rubber tappers allowed cauchero bosses to set up regimes of terror, using torture, mutilation, and murder to keep the collectors in line and producing as much caucho as possible — most infamously, among the Huitoto in the Colombian Putumayo, where anthropologist Michael Taussig has described a “culture of terror, space of death,” and where egregious abuses of indigenous laborers shocked even those hardened to the excesses of extractive colonialism.

Although caucho was considered less valuable than siringa, it could be gathered more quickly. A tapped Hevea tree yielded five to seven pounds of siringa annually; a seringuero might collect about 1,000 pounds of siringo in a year. On the other hand, a mature Castilloa tree could yield 200 pounds of caucho in two days, and a pair of caucheros could collect 1,000 pounds of caucho in a month.

Thus, as opposed to indigenous laborers, many of whom had been recruited to rubber tapping by correrías, slave raids, many mestizos became caucheros voluntarily, lured by the possibility of quick riches, only to find themselves enganchado, hooked, like a fish, by the system of habilitación, debt peonage. Isolated, far from family, deep in the jungle, away from their beloved rivers, when mestizo rubber tappers became sick, they went to indigenous healers, including Yagua and Shipibo shamans. In some cases, the caucheros became apprentices to those who had healed them, and upon their return served their own communities with the skills they had learned.

The rubber boom in eastern Perú saw a massive migration of mestizos from west to east, a shift from agriculture to extraction, and a move from river to jungle. Entire areas were depopulated by fifty percent or more all over the lowlands as rubber contractors removed populations for work. In the town of Moyobamba the population dropped from 15,000 inhabitants to 7,000 between 1859 and 1904; the indigenous village of Jeberos saw a population decline from 3,000 to 300 in the same period.

The rubber bust reversed these trends. The price of rubber fell precipitously on the international market; the tapping of wild trees in the jungle could not compete with Hevea plantations in Asia, where there was no leaf blight. The mestizo rubber tappers migrated westward, back to their riverine homes, their communities, and their swidden gardens, bringing with them the healing practices they had learned from the indigenous people of the jungle.