Assessing the importance of cultural diffusion in the Bantu spread into southeastern Africa

The subsistence of Neolithic populations is based on agriculture, whereas that of previous populations was based on hunting and gathering. Neolithic spreads due to dispersal of populations are called demic, and those due to the incorporation of hunter-gatherers are called cultural. It is well-known that, after agriculture appeared in West Africa, it spread across most of subequatorial Africa. It has been proposed that this spread took place alongside with that of Bantu languages. In eastern and southeastern Africa, it is also linked to the Early Iron Age. From the beginning of the last millennium BC, cereal agriculture spread rapidly from the Great Lakes area eastwards to the East African coast, and southwards to northeastern South Africa. Here we show that the southwards spread took place substantially more rapidly (1.50–2.27 km/y) than the eastwards spread (0.59–1.27 km/y). Such a faster southwards spread could be the result of a stronger cultural effect. To assess this possibility, we compare these observed ranges to those obtained from a demic-cultural wave-of-advance model. We find that both spreads were driven by demic diffusion, in agreement with most archaeological, linguistic and genetic results. Nonetheless, the southwards spread seems to have indeed a stronger cultural component, which could lead support to the hypothesis that, at the southern areas, the interaction with pastoralist people may have played a significant role.

新石器时代（Neolithic）人群的生计以农业为基础，而此前的人群则以狩猎采集为生。新石器时代农业扩张中，由人群迁徙驱动的扩张被称为人口型扩张（demic），由狩猎采集群体融入本地群体所驱动的扩张则被称为文化型扩张（cultural）。众所周知，农业在西非出现后，便扩散至大部分赤道以南非洲地区。有研究提出，此次农业扩张与班图语（Bantu languages）的传播同步发生。在非洲东部与东南部地区，此次农业扩张还与早期铁器时代（Early Iron Age）存在关联。自公元前第一个千年伊始，谷类农业便从非洲大湖地区快速扩散：向东抵达东非沿海，向南则延伸至南非东北部。本研究表明，向南的扩散速度（1.50–2.27 千米/年）显著快于向东的扩散速度（0.59–1.27 千米/年）。这种更快的向南扩张，可能源于更强的文化效应作用。为验证这一可能性，我们将观测得到的扩散范围与基于人口-文化前进波模型（demic-cultural wave-of-advance model）所得出的范围进行对比。研究发现，两次扩张均由人口扩散驱动，这与绝大多数考古学、语言学及遗传学研究结果一致。尽管如此，向南的扩张似乎确实带有更强的文化成分，这一结果可为以下假说提供支撑：在南部地区，与游牧人群的互动或许发挥了重要作用。