Late Pleistocene-to-Holocene Ecological Change and High-Altitude Human Adaptations in Lesotho, Southern Africa

Investigation of Homo sapiens’ paleogeographic expansion into African high-altitude environments is changing how we perceive our species’ adaptions to various ‘extreme’ Pleistocene climates and habitats. Given the historic emphasis placed on sequences from Southern African archaeological sites at or near the coast, it is now crucial to complement such studies with those from the sub-continent’s topographically variable and biologically diverse interior. This project focuses on the paleoecology of Lesotho using plant wax biomarker and stable isotope analyses from archaeological sediments to better understand upland human-environment interactions and significant climatic, environmental, and demographic changes throughout the Pleistocene.

The Kingdom of Lesotho forms the core of southern Africa’s highest mountain system – the Maloti-Drakensberg – with two thirds of the nation situated at elevations higher than 2,000 meters above sea level (m a.s.l.). The Maloti-Drakensberg divides the resource-rich southern African coast from the irregularly distributed resources of the interior, and is separated into two biogeographic regions: the Mesic Highveld and Drakensberg Grassland ecosystems. The Mesic Highveld Grassland is found mainly in western/northwestern Lesotho and in major river valleys, while the Drakensberg Grassland is the dominant bioregion of central and eastern Lesotho. Humans inhabited the cold and ecologically variable environments of the Maloti-Drakensberg at altitudes greater than 1,500 m a.s.l. since at least 80,000 years ago.

Located at the interface between the mountains and the western interior, the uplands of Lesotho and adjacent foothill valleys were particularly valuable to hunter-forager communities during phases of ecological instability and regional drying, specifically in relation to the more uneven resource distributions of environments further inland. The ecotonal setting and ability to access both the mountains and lowlands via mobile foraging and social networking provided enhanced long-term stability for human populations.

This project seeks to open a new window into Lesotho’s high-altitude settings through the application of compound-specific plant wax biomarkers, mainly normal (n-) alkanes and n-alkanoic acids. These compounds provide detailed insights into climatic and environmental variables in this critical montane heartland, as well as the ecological benefits the region must have provided in a Late Pleistocene setting. Additionally, the use of wax biomarkers in upland archaeological sites of Lesotho offers opportunities to study past distributions of C₃ and C₄ vegetation and the impact changes in temperature and precipitation would have had on plant and animal resources from about 60,000 years ago into the present. Because these high-altitude settings were susceptible to climate change, cold and dry conditions, and patchy resource distributions, the archaeology and paleoecology of Lesotho provide important perspectives regarding major adaptive challenges humans faced, as well as population interactions along the Maloti-Drakensberg.