The coevolution of languages, peoples and environments in Central Africa’s Kwilu-Kasai region since ∼1000 BCE: A dialogue with Jan Vansina

In this article, Jan Vansina’s essay on the deep-time population history of the Kwilu-Kasai region, now more than half a century old, is revisited through the kaleidoscopic lens of newly collected linguistic, archaeological, palaeoecological and genetic evidence collected between 2018 and 2023. In contrast to Vansina’s view of the region as a terminus for the settlement of diverse Bantu speech communities, the area was likely an important center of diversification and expansion for early Bantu speakers. Under a drier climate favoring the increase of grassland and open woodland around Idiofa but not a general loss of the forest cover, Bantu speakers most probably started occupying the region from the 4th century BCE onwards. Pottery-producing settlements first emerge along the Kwilu River, i.e., at Luani (371–148 BCE) and Lukombe (357–27 BCE), and then near Idiofa (146–18 BCE), where the earliest evidence for iron metallurgy marks the actual start of the Early Iron Age (146 BCE-750CE) south of the Congo rainforest. The first settlers lived in small and enclaved communities without much mutual communication. These were perfect conditions for early divergence within the Bantu language family’s major West-Coastal Bantu branch. While modern language data situate the West-Coastal Bantu homeland between the Kasai and Kamtsha Rivers, this zone was only settled towards the beginning of the common era based on the currently available archaeological data. This apparent mismatch between archaeology and historical linguistics might be due to subsequent processes of language death and population relocation and restructuring. Confirming Vansina’s idea that modern-day Kwilu-Kasai communities do not directly descend from the region’s earliest Bantu-speaking settlers, significant population reshuffling did indeed occur after the Early Iron Age. During the so-called ‘hiatus period’ (750–1450 CE), human activity contracted to a few refuge areas, especially near the modern towns of Bandundu and Idiofa, and the vegetation underwent an irreversible climate-induced shift to open habitats, possibly connected to the Medieval Climate Anomaly. During the Late Iron Age, the study area was rapidly resettled, first in the south (15–16th c. CE), and then in the north (17–18th c. CE), and large cross-regional exchange networks developed. In line with oral histories still existing among Kwilu-Kasai peoples today and with the clans and political and social institutions they share, the region underwent a very advanced demographic, linguistic and cultural integration in the four to five centuries preceding the start of European colonization, which may have involved populations no longer present there today, such as Ubangi-speaking groups.