Figure 3. Adding the human population to the previous model.
As in the previous model, a festival is declared whenever the number of pigs exceeds the number of humans. Figure 4 shows the simulated cycles in the human and pig populations. The simulation begins with 40 pigs, 140 humans and proceeds with DT set at 1 year.
Figure 4. Repeating cycles in human and pig populations.
The rapidly growing pig population triggers the first festival around the tenth year of the simulation. The new model shows a 12% decline in the human population as well as the major drop in the pig population after the first festival. Figure 4 shows three festivals with approximately 11 years between festivals. The simulation also shows that the two populations would be held in check by the reoccurring festivals and warfare.
This simulation is similar to more complicated simulations with the original model by Shantzis and Behrens (1973, 275). They were particularly impressed by the long term stability of the populations and concluded that "the Tsembaga unconsciously use the pig herd as both an information monitor and a homeostat in a complex, automatic population control system."
Shantzis and Behrens were concerned about the long term size of the population if warfare was disallowed by outside administrators. Figure 5 shows the population trends in the introductory model if the human kill fraction is set to zero. With a net birth rate of 1.3%/yr, the human population grows to around 600 by the end of the simulation. The pig population grows as well since the only limit on the number of pigs is the number of humans willing to care for them. In the year before the final festival, there would be around 600 pigs and 600 humans.
Figure 5. Simulated growth in pig and human populations if warfare is disallowed.