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Spatial sampling bias influences our understanding of early hominin evolution in eastern Africa

Nature Ecology & Evolution volume 8, pages 2113–2120 (2024)Cite this article

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Abstract

The eastern branch of the Eastern African Rift System (EARS) is the source of a large proportion of the early hominin fossil record, but it covers a tiny fraction (ca. 1%) of the continent. Here we investigate how this mismatch between where fossils are preserved and where hominins probably lived may influence our ability to understand early hominin evolution, using extant mammals as analogues. We show that the eastern branch of the EARS is not an environmentally representative sample of the full species range for nearly all extant rift-dwelling mammals. Likewise, when we investigate published morphometric datasets for extant cercopithecine primates, evidence from the eastern branch alone fails to capture major portions of continental-scale cercopithecine cranial morphospace. We suggest that extant rift-dwelling species should be used as analogues to place confidence intervals on hominin habitat reconstructions. Furthermore, given the north–south orientation of the eastern branch of the EARS, morphoclines that are not aligned along this major north–south axis are likely to be poorly sampled by sites in the eastern branch. There is a pressing need for research on the geography of early hominin morphoclines to estimate how morphologically representative the hominin fossil sample from the eastern branch may be.

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Fig. 1: Map of Africa with selected early hominin fossil sites labelled with yellow dots.
Fig. 2: Distributions of environmental variables across the full ranges of 106 rift-dwelling taxa compared with the within-rift subset.
Fig. 3: Geographic distribution of cranial specimens analysed (open black circles) overlaid onto the species range maps drawn from IUCN (ranges of each species are plotted in different colours).
Fig. 4: Locations of 500 ‘random’ rifts placed on the African continent.
Fig. 5: Histograms showing the sampling efficiency of ‘random’ rifts in guenons+ and baboons compared with the sampling efficiency of the actual eastern branch (vertical red line).

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Data availability

Data files necessary for producing the figures and analyses are available on Github at https://github.com/wabarr/outside-rift.

Code availability

Code necessary for producing the figures and analyses is available on Github at https://github.com/wabarr/outside-rift.

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Acknowledgements

Special thanks to A. Cardini, S. Elton and S. Frost for generously providing access to datasets and providing spatial coordinates. We gratefully acknowledge the financial support of the Center for the Advanced Study of Human Paleobiology at GWU, the GWU Department of Anthropology and the GWU Office of the Provost. Thanks to members of the PAPER discussion group for fruitful discussion, to S. McPherron and S. Elton for helpful feedback after a conference presentation of some of the ideas in this paper, and to C. Campisano for answering our geological questions about the rift.

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  1. Department of Anthropology and Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington DC, USA

    W. Andrew Barr & Bernard Wood

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W.A.B. devised the research question, compiled the datasets, wrote all code, interpreted all statistical analyses, wrote the first draft of the paper and revised the paper. B.W. contributed to the development of the research question, consulted on analytical strategy and revised the paper.

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Correspondence to W. Andrew Barr.

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Supplementary Figs. 1–3 and Tables 1–3.

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Supplementary Video 1

A GIF animation showing the placement of random sampling units on the continent of Africa.

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Barr, W.A., Wood, B. Spatial sampling bias influences our understanding of early hominin evolution in eastern Africa. Nat Ecol Evol 8, 2113–2120 (2024). https://doi.org/10.1038/s41559-024-02522-5

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