Background on the Tsembaga
In 1968, Roy Rappaport published Pigs for the Ancestors,
the classic anthropological study of the Tsembaga tribesmen in the New Guinea
highlands. Rappaport was interested in the Maring-speaking peoples of eastern
New Guinea because of their relative isolation and interesting culture.
The Maring practice slash-and-burn agriculture in which only a portion of their total acreage is cultivated at any given time. The area is cleared of forest and burned over. The burning clears away the underbrush for planting and produces a nutrient ash residue which adds to soil fertility. The Maring cultivate root crops which provide their main sustenance. The crops in one area are harvested for a year or two, depleting the nutrients in the area. When yields decline, the Maring move to a new area and repeat the process of clearing, burning and cultivation. The previously cultivated land quickly becomes covered by tropical rain forest. It will be suitable for clearing and cultivation again after fifteen or twenty years. The long fallowing requirement means that the Maring must limit cultivation to a small percentage of the arable land. If they maintain a twenty year rotation period, for example, only around 5% of the land would be under cultivation at one time.
The Tsembaga Subclan
This exercise introduces you to the Tsembaga, a Maring subclan living on 1,000 acres of arable land in the heart of a virgin forest. At the time of Rappaport's study, the clan numbered around 200 people. The Tsembaga herd pigs, and their domestic herd could range in size from 50 to 200 pigs depending on when the pigs were counted. The pigs are highly valued, but not necessarily for their contribution to human sustenance. An owner of many pigs is accorded both respect and material reward, and pigs are not normally killed except to meet religious or family obligations.
When well fed, the pig herd grows at around 14%/year, so
they would become extremely numerous within a few decades. Imagine, for
example, that there are 100 pigs when the tribe is about to relocate their
gardens to a new area. They might return to the current spot in around 20
years. How large do you think the pig herd would be when they return to
the current spot?
If you recall the doubling time rules from appendix B, your answer would be 1,600 pigs. Now, think of the work load for a tribe of 200. The job of tending to the pigs falls mainly on the Tsembaga women. If half the population were women, each woman would be responsible for sixteen pigs! This workload raises a question
what to do about the pigs?
The answer is the pig festival -- an elaborate ritual in
which around 85% of the pigs are slaughtered. The festival is initiated
when the growing pressures of tending to the pigs becomes excessive. The
festival is marked by a major feast to consume the pigs and to discuss relations
with neighboring clans.
The festival also marks the time on the Tsembaga calendar when internal restrictions on warfare are removed. War with neighboring clans breaks out almost immediately, and conflict usually continues for a year. The main objective of warfare is to redress past grievances, and conflict continues as each side attempts to "get even." Inevitably, warfare does not produce the desired results, and the warring parties negotiate a temporary truce. The Tsembaga may experience 12% fatalities by the time the truce is declared. The truce allows them to return to routine life. Internal restrictions against warfare are reinstated, and they apply until the next pig festival.
A System Dynamics Model
Shantzis and Behrens (1973) published a system dynamics
model of the Tsembaga system. It simulates the human population, the pig
population and the food supply. They were particularly interested in the
role of the pig festival and warfare as a "population control mechanism,"
and they were concerned about the future of the system if war is disallowed
by outside administrators. Their model deals with the complexities of simulating
land yields, food production, sharing of food among pigs and humans, growth
in the pig and human populations and the triggering of the pig festivals.
To their credit, Shantzis and Behrens simulate all of these factors as endogenous
variables. These pages begin with some introductory models to build our
understanding of the dynamics studied by Shantzis and Behrens.