Dating the skull from Broken Hill, Zambia, and its position in human evolution

Abstract

The cranium from Broken Hill (Kabwe) was recovered from cave deposits in 1921, during metal ore mining in what is now Zambia1. It is one of the best-preserved skulls of a fossil hominin, and was initially designated as the type specimen of Homo rhodesiensis, but recently it has often been included in the taxon Homo heidelbergensis2,3,4. However, the original site has since been completely quarried away, and—although the cranium is often estimated to be around 500 thousand years old5,6,7—its unsystematic recovery impedes its accurate dating and placement in human evolution. Here we carried out analyses directly on the skull and found a best age estimate of 299 ± 25 thousand years (mean ± 2σ). The result suggests that later Middle Pleistocene Africa contained multiple contemporaneous hominin lineages (that is, Homo sapiens8,9, H. heidelbergensis/H. rhodesiensis and Homo naledi10,11), similar to Eurasia, where Homo neanderthalensis, the Denisovans, Homo floresiensisHomo luzonensis and perhaps also Homo heidelbergensis and Homo erectus12 were found contemporaneously. The age estimate also raises further questions about the mode of evolution of H. sapiens in Africa and whether H. heidelbergensis/H. rhodesiensis was a direct ancestor of our species13,14.

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Fig. 1: The Broken Hill cranium (E686), discovered at the Broken Hill mine, Zambia, in 1921.
Fig. 2: U-series results.

Data availability

The data that support the findings of this study are included in the Supplementary Information. Additional data are available from the corresponding authors upon reasonable request.

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Acknowledgements

Aspects of this research were funded by ARC grants DP0664144 (R.G. et al.) ‘Microanalysis of human fossils: new insights into age, diet and migration’, DP0666084 (R. G. Roberts, R.G. et al.) ‘Out of Africa and into Australia: robust chronologies for turning points in modern human evolution and dispersal’, DP110101415 (R.G. et al.) ‘Understanding the migrations of prehistoric populations through direct dating and isotopic tracking of their mobility patterns’. C.S. acknowledges support from the Calleva Foundation and the Human Origins Research Fund, as well as the assistance of past and present members of staff at the Natural History Museum: R. Kruszynski, L. Buck, L. Crété, G. Comerford, L. Cornish, C. Collins, L. Harvey, J. Galway-Witham and P. Brewer. Images and copyrights of Extended Data Figs. 1a, 2a, 3 were provided by the Mary Evans Picture Library.

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Authors

Contributions

R.G. and C.S. wrote the paper with contributions from all co-authors. R.G. carried out the ESR measurements, R.J.-B. ESR spectrum deconvolution. Laser-ablation analyses were performed by R.G. and A.P., with the support of S.E. and L.K.; U-series solution analyses by G.M., F.M. and T.C.; gamma-spectrometry measurements by R.G.; uranium analysis of tooth enamel by M.A.; microfaunal analysis by C.D.; macrofaunal analysis by the late J.B. M.R. provided the site history and tracked down some of the sediment samples.

Corresponding authors

Correspondence to Rainer Grün or Chris Stringer.

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The authors declare no competing interests.

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Peer review information Nature thanks Christophe Falguères, Michael Storey, Kira E. Westaway and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Photos of the skull shortly after its discovery.

a, The cranium at the location in which it was found34. © Illustrated London News Ltd/Mary Evans. b, c, Frontal view (b) and lateral view (c) before the matrix was removed. Images from the Archive of the Natural History Museum.

Extended Data Fig. 2 Divergent recollections of the Bone Cave.

a, Drawing as instructed by Harris34. © Illustrated London News Ltd/Mary Evans. b, Re-drawing of a sketch by White37.

Extended Data Fig. 3 Photograph of the site with find spot of the skull.

© Illustrated London News Ltd/Mary Evans.

Extended Data Fig. 4 Broken Hill human fossils sampled for direct dating and results of associated small mammals.

a, Partial os coxa (E719). b, Femoral fragment (E907). c, Femoral midshaft (EM793). d, Tibia (E691). e, SEM image of Broken Hill O. angoniensis mandible fragments with lower molar. f, SEM image of Broken Hill O. angoniensis M3 (7 laminae). g, h, Drawing of the lower (g) and upper (h) first molars of S. campestris from the cave deposits. i, Fossils and modern Otomys M3 scatter plot of length versus width in mm. s.e., Sterkfontein Extension; Olduvai Bed I, Bed II, Bed IV; KB, Kromdraai B. Modern specimens of O. angoniensis and O. saundersae have been added for comparison. j, Scatter plot (length versus width in mm) of the modern and fossil Saccostomus species upper first molar. Saccostomus major is a Pliocene species found in Laetoli (3.7–2.5 Ma); Saccostomus cf. mearnsi was described in Olduvai bed I (1.7–1.6 Ma), bed IV: S. cf. campestris from Olduvai bed IV (0.8 Ma), Saccostomus sp. from East Turkana (1.6 Ma), S. campestris from Broken Hill. Modern S. mearnsi live in East Africa and modern S. campestris live in South Africa. The correlation lines are indicated here.

Extended Data Fig. 5 Details of the laser ablation U-series analyses.

a, U-series results by laser ablation, solution ICP-MS and gamma spectrometry on the femoral midshaft (EM793). All data points are means from the isotopic measurements with 2σ errors. The laser-ablation profiles consist of n = 33 (Supplementary Table 7) and the TIMS of n = 5 (Supplementary Table 3) measurements across the bone. The gamma spectrometry is carried out on the whole sample (n = 1) (Supplementary Table 8). b, c, Laser sampling positions on the basioccipital fragment. Red, 2014 234U/238U measurements; green, 2016 230Th/238U measurements. b, outer surface. c, inner surface. dg, Results of average laser-ablation measurements on the basioccipital fragment (2σ errors). For locations, see b and c. Outside, laser-ablation depth profiles (n = 4) were each averaged for the calculation of the 230Th/238U and 234U/238U isotope ratios and resulting ages (Supplementary Tables 4, 5). Inside, laser-ablation depth profiles were averaged for the 234U/238U isotope ratio (n = 3) and for the 230Th/238U isotope ratio (n = 8) and resulting ages (Supplementary Tables 4, 5). d, 234U/238U measurements. e, 230Th/238U measurements. f, Age results. g, Initial 234U/238U ratios. All profiles consist of n = 30 data points (Supplementary Table 6). h, Vials with sediment scraped off the skull (sediment from E686 in Supplementary Table 11).

Extended Data Fig. 6 External dose-rate distributions for different models.

Models were generated using the materials listed in Supplementary Table 11. In all models the cave roof is composed of solid material (rocks and breccia). a, The cave floor is composed of any material. b, The cave floor is composed of loose sediment and breccia. c, The cave floor is composed of loose sediment. d, The floor only consists of sediment from E686. e, Sorted dose rates for the lower 50% of results.

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Grün, R., Pike, A., McDermott, F. et al. Dating the skull from Broken Hill, Zambia, and its position in human evolution. Nature 580, 372–375 (2020). https://doi.org/10.1038/s41586-020-2165-4

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