UNIVERSITY PARK, Pa. — Humans have used fire for millennia to lure out game when hunting and to convert woodland to agricultural land, leaving their mark on the landscape. New archaeological and paleoenvironmental evidence from Lake Malawi, Africa, shows that the effects on the landscape of humans’ use of fire is tens of thousands of years older than previously thought, according to an international team of researchers.
“The vegetation in the area around Lake Malawi is a little mysterious,” said Sarah Ivory, assistant professor of geosciences at Penn State. “It’s right in the middle of the tropics, and we think of tropical forests as being these icons of biodiversity where all the world’s species are housed. Yet here, in the middle of tropical Africa, is this extensive forest that is really species poor.”
Fire geographers and modern ecologists have thought that humans may have played a role in shaping the landscape, but how long ago humans impacted the landscape and exactly how they did so remained unclear until now, Ivory said.
The researchers studied dense clusters of stone artifacts, some dating as far back as 92,000 years, collected from the northern shores of the lake, and fossil pollen and charcoal samples taken from a sediment core drilled from the lakebed. The evidence, when analyzed separately, raises more questions than answers, but combined it tells a story of early modern humans using fire in a way that prevented regrowth of the region’s forests and created the sprawling bushland that exists today, according to the researchers. They reported their findings today, May 5, in Science Advances.
“This is the earliest evidence I have seen of humans fundamentally transforming their ecosystem with fire,” said Jessica Thompson, assistant professor of anthropology at Yale University. “It suggests that by the Late Pleistocene, humans were learning to use fire in truly novel ways. In this case, their burning caused replacement of the region's forests with the open woodlands you see today.”
The scientists identified the artifacts as being of Middle Stone Age type, which describes a widespread way of making stone tools across Africa for at least the last 315,000 years. During this time, the earliest modern humans made their appearance, with the African record showing the earliest significant advances in cognitive and social complexity.
“We got interested in the region because we wanted to investigate the start time of the Middle Stone Age,” said David Wright, professor of archaeology at the University of Oslo, Norway. “But we couldn’t understand why all of our sites were dating to the end of it.”
Thompson and Wright had logged several field seasons of archaeological work before a conversation with Ivory made the patterns in their data make sense.
“Of the entire 600-thousand-year record captured in the sediment core, the last 85,000 years were the most ecologically interesting,” said Ivory, who also holds an appointment in Penn State’s Earth and Environmental Systems Institute. “I suspected that humans might be responsible for the unusual patterns I was seeing in the charcoal and vegetation records, and the archaeological data supported it.”