Ecology and demography of early Homo sapiens: a synthesis of archaeological and climatic data from eastern Africa

ABSTRACT

Eastern Africa maintains a key position in debates surrounding the emergence of Homo sapiens across Africa. Extensive research in the region has revealed a rich fossil record in association with a ‘generic’ but variable Middle Stone Age (MSA) material culture, providing an important laboratory for testing hypotheses about the behavioural evolution of our species. For example, multiple archaeological studies of the eastern African MSA note a link between the distribution and density of sites, archaeological diversity and environmental conditions, with ecology and demography often cited as key drivers of cultural evolution. This article formulates new hypotheses using theoretical models of complex fitness landscapes of evolution and reviews the archaeological and climatic records of Middle-late Pleistocene eastern Africa in the light of these ideas. It proposes that evidence from eastern Africa implicates much of the region as a refugial zone within Pleistocene Africa, providing consistently suitable conditions for survival that were characterised by high and changing biodiversity, facilitating population growth and interconnectivity as well as material culture diversification. Interactions between different evolutionary processes likely resulted in the complex cultural mosaic observed across Africa, including the appearance of ‘specific’ innovations against a backdrop of more ‘generic’ MSA elements.

RÉSUMÉ

L’Afrique de l’Est occupe une position clé dans les débats autour de l’émergence de l’Homo sapiens en Afrique. Les recherches approfondies dans la région ont révélé de riches archives fossiles en association avec une culture matérielle ‘générique’ mais variable de l’Âge de Pierre Moyen (MSA), fournissant un laboratoire important pour tester les hypothèses sur l’évolution comportementale de notre espèce. Par exemple, de multiples études archéologiques sur le MSA d’Afrique de l’Est ont relevé un lien entre la répartition et la densité des sites, la diversité archéologique, et les conditions environnementales. L’écologie et la démographie sont souvent citées comme moteurs clés de l’évolution culturelle. Cet article formule de nouvelles hypothèses en utilisant des modèles théoriques de ‘fitness landscapes’ évolutionnaires complexes, passant en revue les archives archéologiques et climatiques de l’Afrique de l’Est du Pléistocène moyen-tardif à la lumière de ces idées. Nous proposons que les données provenant d’Afrique de l'Est impliquent une grande partie de la région comme zone refuge au sein de l’Afrique au Pléistocène, offrant des conditions de survie qui restèrent appropriées de façon durable, caractérisées par une biodiversité élevée et changeante, facilitant la croissance et l’interconnectivité de la population ainsi que la diversification de la culture matérielle. Les interactions entre différents processus évolutionnaires ont probablement abouti à la mosaïque culturelle complexe que l’on observe à travers l’Afrique, y compris l’apparition d’innovations ‘spécifiques’ sur fond d’éléments MSA plus ‘génériques’.

KEYWORDS:

• Modern human evolution
• Middle Stone Age
• ecological refugia
• lithic technology
• palaeoenvironmental change
• complex fitness landscape

Acknowledgements

I should first like to acknowledge the British Institute in Eastern Africa for supporting this research paper. I should also like to thank Francesco d’Errico, Paloma de la Peña, Chris Stringer, Tim White, Radu Iovita, Chris Scott and Larry Barham for permission to use their images in this article. Finally, I thank Matt Grove, John Gowlett, Manuel Will, James Blinkhorn and an anonymous reviewer for their constructive feedback. This work stems from my PhD research, which was funded by the Arts and Humanities Research Council North-West Consortium Doctoral Training Partnership (AH/R012792/1), the Leakey Foundation (Movement, interaction, and structure: modelling population networks and cultural diversity in the African Middle Stone Age), the Wenner Gren Foundation (Gr. 10157) and the Lithic Studies Society (Jacobi Bursary, 2020).

Data availability statement

Data and code to reproduce Figures 1, 4 and 5 in this article can be found here: https://github.com/lucytimbrell/ecodemo

Additional information

Notes on contributors

Lucy Timbrell

Lucy Timbrell is a Postdoctoral Research Fellow at the Max Planck Institute of Geoanthropology, Germany, and the Department of Archaeology, Classics and Egyptology, University of Liverpool, United Kingdom. She completed her PhD at the University of Liverpool in 2023 exploring population dynamics among Middle Stone Age populations in eastern Africa. She uses geometric morphometrics, eco-cultural niche modelling and GIS, among other quantitative approaches, to investigate the articulation of material culture and palaeoenvironments in both Africa and Europe.