The Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) has participated in a study just published in the journal Proceedings of the National Academy of Sciences (PNAS), on the progressive aridification of East Africa over the last half-million years and its implications for human evolution. According to this analysis, the evidence for a variable and progressively dryer climate coincides with an important change in stone-tool-making and the appearance of modern Homo sapiens.

This study, based on lake sediment cores 194 m long, collected in Lake Magadi in southern Kenya, is the first to provide a continuous environmental context for the diverse archaeological and paleontological evidence recovered from the basins in the Rift Valley.

“While the evolution of the hominins had previously been related to environmental changes, the cores from Lake Magadi provide the first detailed link between climate change and the events known about from the archaeological record of the region”, says Mark Sier, geochronologist and archaeologist at the University of Oxford, who carried out part of the magnetostratigraphic analyses in the Archaeomagnetism Laboratory of the CENIEH.

A critical transition
As the study's lead author, Richard Owen, of Hong Kong Baptist University, explains, "There is a big gap in the records between the last Early Stone Age tools 500,000 years ago and the appearance of Middle Stone Age tools about 320,000 years ago.

Our results plugged that gap with a continuous environmental record, and a critical transition took place during this gap, a period for which archaeologists have unearthed evidence of a leap in early humans' abilities to make, use and trade stone tools”, adds Owen.

The stone tools found did not change much between 1.2 million and a half-million years ago. Then suddenly, after 500,000 and before 320,000 years ago, and coinciding with the aridification of the region, the tools became more sophisticated and were transported over longer distances.

International project
“Now we can say when the environment changed and then compare that to the archaeological evidence of the region", states Andrew Cohen, of the University of Arizona, director of the Project Hominin Sites and Paleolakes Drilling Project (HSPDP), of which this work forms part.
The HSPDP is an international and multidisciplinary project whose objective is to study the relationship between human evolution and climate change by drilling in paleolakes situated close to the most important archaeopaleontological sites in the world.