Firebending has given humans dominance over the natural world. A study by Yale provides the first evidence to date that ancient humans dramatically alter entire ecosystems with flames.
The study, published May 5 in the journal Scientific progress, combines archaeological evidence – dense clusters of stone artifacts dating back to 92,000 years ago – with paleoenvironmental data from the northern shores of Lake Malawi in East Africa to document that the first humans were engineers in ecosystem. They used fire in a way that prevented the regrowth of the region’s forests, creating a sprawling bush that exists today.
Yale paleoanthropologist Jessica Thompson describes the first evidence that humans are altering their ecosystem by fire in this video.
“This is the first evidence I’ve seen of humans fundamentally transforming their ecosystem with fire,” said Jessica Thompson, assistant professor of anthropology in the Faculty of Arts and Sciences and lead author of the article. “This suggests that by the Late Pleistocene, humans were learning to use fire in really new ways. In this case, their burning caused the forests in the region to be replaced by the open forests you see today.”
Thompson is the author of the study with 27 colleagues from institutions in the United States, Africa, Europe, Asia and Australia. Thompson led the archaeological work in collaboration with the Department of Museums and Monuments of Malawi; David Wright of the University of Oslo, who led efforts to date the archaeological sites in the study; and Sarah Ivory of Penn State, who led the paleoenvironmental scans.
The artefacts examined by the researchers are of the type produced across Africa in the Middle Stone Ages, a period dating back at least 315,000 years. The first modern humans emerged during this period, with African archaeological records showing significant advances in cognitive and social complexity.
Thompson and Wright recorded several seasons of fieldwork of archaeological work in the area before a conversation with Ivory helped them understand the patterns they observed in their data. Researchers found that the regional archaeological record, its ecological changes, and the development of alluvial cones near Lake Malawi – an accumulation of eroded sediment from the region’s highlands – dated from the same period of origin, suggesting that they were connected.
The water levels in Lake Malawi have fluctuated considerably over the ages. During the lake’s driest periods, the last of which ended about 85,000 years ago, it shrank into two small bodies of salt water. The lake has recovered from these arid expanses and its levels have remained high ever since, according to the study.
Archaeological data was collected from more than 100 pits dug hundreds of kilometers of the alluvial cone that developed during this period of stable lake levels. Paleoenvironmental data are based on counts of pollen and charcoal that settled to the bottom of the lake bed and were then recovered in a long sediment core drilled from a modified barge.
According to the researchers, the data revealed that a peak in charcoal accumulation occurred shortly before the region’s species richness flattened – the number of distinct species that inhabit it. Despite the lake’s consistently high levels, which imply greater ecosystem stability, species richness stabilized after the last arid period based on information from fossilized pollen collected from the lake bed, according to study. This was unexpected because during previous climate cycles, rainy environments had produced forests that provide rich habitat for an abundance of species, Ivory explained.
“The pollen that we see in this last period of stable climate is very different from before,” she said. “Specifically, trees that indicate dense and structurally complex forest covers are no longer common and are being replaced by pollen from plants that are resistant to frequent fires and disturbances.”
The increase in archaeological sites after the last arid period, coupled with the ear of charcoal and the lack of forest, suggests that people were manipulating the ecosystem with fire, the researchers conclude. The magnitude of their long-term environmental impact is generally associated with farmers and ranchers, rather than hunter-gatherers. This suggests early ecological manipulation on par with modern people, and may also explain why archaeological records were formed.
The fires, coupled with climate change, created the conditions that allowed the preservation of millions of artefacts in the region, the researchers said. “Dirt rolls downhill unless there’s something to stop it,” Wright said. “Remove the trees, and when it rains, there is a lot of earth coming down into this environment.”
Previous transitions from dry to wet conditions in the region did not yield a similar alluvial fan and were not preceded by the same charcoal peak, the researchers noted.
It’s unclear why people were burning the landscape, Thompson said. It is possible that they were experimenting with controlled burns to produce mosaic habitats suitable for hunting and gathering, a behavior documented among hunter-gatherers. It may be that their fires have gotten out of hand or that there are simply a lot of people burning fuel in their surroundings providing them with warmth, cooking or socializing, she explained.
“Somehow it’s caused by human activity,” she said. “This shows that the first peoples, over a long period of time, took control of their environment rather than being controlled by it. They changed entire landscapes, and for better or for worse, this relationship with our environments continue today. “
This work was funded by the Australian Research Council, National Geographic-Waitt Foundation, Wenner-Gren Foundation, University of Queensland Archaeological Field School, Korean Research Foundation Global Research Network, Deutsche Forschungsgemeinschaft, Emory University and the Belmont Forum.