Simulating the effects of local interactions on the expansion of the Bantu during Neolithic
Résumé
Axtell (1999) distinguishes different motivations for using agent-based computation in the social sciences, opposing the use of simulation as a complement for a mathematical model and when “writing down equations is not a useful activity”. This later point of view matches the study of Bantu expansion to Southern and Eastern Africa between 1000 BP and 1000 AD. Use of linguistic and genetic studies give some information over the absence or presence of Bantu groups at some different dates but the information is globally deficient. An agent-based model (HUME) has been developed in order to reconstruct "stylized facts" in the way Bantu expansion occurred: demographic growth, speed of migration, preferred routes (costal road, savannah, forest, rivers, etc.). Particular attention has been put on the effect of the interactions between forager-hunter groups and Bantu groups on the rhythm and form of the spatial expansion process. Hence, a debate exists today amongst paleolinguists and paleohistorians on how equatorial forest present in Central Africa have been crossed by Bantus groups, taking into account that Bantus groups dislike going into the forest, inhabited by forest foragers groups. Questions remain unsolved to what extend forest foragers helped Bantus groups to cross the equatorial forest, or if contact between Bantus and forest foragers was common at Neolithic era. A strong asymmetry today characterizes their relationships and empirical knowledge based on genetic and linguistic observation today cannot discriminate whether this asymmetry have been present from the start or have develop over time.
HUME (HUman Migration and Environment) model aims at exploring "numerically" the Bantu expansion and to test the effects on the forms of spatial expansion of different forms of interaction between Bantu groups and forest-foragers groups. Thus, we have been able to test different scenarios about how the Bantu have expanded toward the South. Space is heterogeneous in the model with three types of areas (sea, savannah, forest) that impact the ability of groups to extract resources and to move. This spatial heterogeneity is a cornerstone of the methodology adopted for it allows us to assess the respective role played by social interactions betweens groups and by interactions betweens groups and the environment in the spatial forms of the crossing of equatorial forest by Bantus. Various initial spatial configurations are tested and the expansion of the Bantu are measured by indicators to assess i) the success or failure of the colonization of the entire space, ii) the trajectories of settlement, particularly in relation to the obstacle of the forest. We therefore use spatial simulation as a way to build “stories” that are at the same time consistent with stylized fact already known by specialists of the Neolithic era and realistic enough to fertilize the scientific approach on unknown part of the system, here for instance the complex interactions between Bantus groups and forest foragers groups.