A new study says that the activities of early humans — and not simply a dramatic shift in climate — played a significant role in transforming the ancient rainforests of Central Africa into savanna. In an analysis of sediment cores taken from the mouth of the Congo River, a team of scientists found evidence that weathering of clay sediment samples, which had been consistent for thousands of years, intensified abruptly about 3,000 years ago, indicating a significant increase in deforestation. According to their study, published online in Science, this shift coincided with the arrival of Bantu-speaking farmers from present-day Nigeria and Cameroon. While this forest disturbance was likely triggered by prolonged dry spells that destroyed rainforest, as previous research has concluded, the Science study indicates that climate change was exacerbated by human land use, including the clearing of forests for farming and iron-smelting. Germain Bayon, of the French Research Institute for Exploration of the Sea and lead author of the study, said the findings illustrate how a combination of climate and human activity can affect the environment. “Humans can have a huge impact on natural processes,” he said.