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The archaeology of East Africa during the last ~65,000 years plays a central role in debates about the origins and dispersal of modern humans, Homo sapiens. Despite the historical importance of the region to these discussions, reliable chronologies for the nature, tempo, and timing of human behavioral changes seen among Middle Stone Age (MSA) and Later Stone Age (LSA) archaeological assemblages are sparse. The Kisese II rockshelter in the Kondoa region of Tanzania, originally excavated in 1956, preserves a ≥ 6-m-thick archaeological succession that spans the MSA/LSA transition, with lithic artifacts such as Levallois and bladelet cores and backed microliths, the recurrent use of red ochre, and >5,000 ostrich eggshell beads and bead fragments. Twenty-nine radiocarbon dates on ostrich eggshell carbonate make Kisese II one of the most robust chronological sequences for understanding archaeological change over the last ~47,000 years in East Africa. In particular, ostrich eggshell beads and backed microliths appear by 46–42 ka cal BP and occur throughout overlying Late Pleistocene and Holocene strata. Changes in lithic technology suggest an MSA/LSA transition that began 39–34.3 ka, with typical LSA technologies in place by the Last Glacial Maximum. The timing of these changes demonstrates the time-transgressive nature of behavioral innovations often linked to the origins of modern humans, even within a single region of Africa.

East Africa is central to understanding the biological and behavioral origins of modern humans, because of the presence of multiple early fossils attributed to Homo sapiens and early examples of Middle Stone Age (MSA) technology associated with them [1–3]. In part because of its geographic proximity to potential exit points along the Nile Valley and Horn of Africa, the region also features prominently in discussions of human population dispersals across and out of Africa by approximately 65,000 years ago (~65 ka) if not before [4–7]. However, our understanding of the social and environmental contexts of modern human populations in East Africa since ~65 ka remains poorly resolved due to a number of issues, prominent among them being the rarity of well-dated archaeological sequences that include terminal MSA and early Later Stone Age (LSA) assemblages (reviewed in [3, 8]). Broadly, the MSA/LSA transition consists of a series of technological and behavioral changes such as artifact miniaturization, expanded dietary breadth, and the increased use of symbolic artifacts and non-local materials that have been correlated with the origin of modern human cognitive abilities [9], increases in local population size, density [2, 10, 11] or inter-connectedness, potentially linked with environmental change [12, 13], and human dispersals [14].

For East Africa in particular, no single archaeological sequence has been able to satisfactorily address whether the MSA-LSA transition is the summation of long-term, incremental changes in human behavior or a rapid behavioral revolution spurred by genetic or cognitive change as has been debated for nearly two decades [2, 9]. Available data have been used to suggest that the East African MSA-LSA transition was a complex, incremental process spanning 15 kyr or less beginning as early as 55 ka [3], but this hypothesis is based on comparisons across a series of poorly dated and irregularly described sequences. The small East African sample of sites with published and well-described MSA-LSA sequences (Fig 1) includes Magosi in Uganda, Enkapune ya Muto and GvJm22 (Lukenya Hill) in Kenya, and Mumba, Nasera, Mlambalasi and Magubike rockshelters, and perhaps Olduvai Gorge in Tanzania [15–19]. In addition to unconformities and incompletely understood sedimentary histories, the site sample has poor chronological resolution due to numerous infinite radiocarbon (14C) age estimates or other “dates” using unreliable materials and excavation methods that frequently mixed discrete strata. Mumba rockshelter has a robust chronology based on 14C and amino acid racemization dates on ostrich eggshell (OES) and optically stimulated luminescence ages on sediments, and its archaeological sequence is one of the most important in the region [2, 17, 20]. However, it is also one of the most difficult to interpret, as various parts of the cave have been differentially sampled and reported by four different teams operating at the site since the 1930s, with divergent interpretations based on temporal changes in lithic technology used to support hypotheses of either rapid or gradual shifts across the MSA/LSA transition [17, 18, 21, 22].

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