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Nature

Humans Have Managed Landscapes With Fire For Almost 100,000 Years

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Stephen Luntz

Freelance Writer

clockMay 6 2021, 16:58 UTC
malawi dig

The abundance of human artifacts found at Sadala South I site near Karonga, Malawi coinciding with the increase in charcoal is one of the ways we know these firest were set by humans. Image Credit: Jessica Thompson

Ancient myths recognized how important controlling fire was to humanity, making us a threat to the gods. The timing of this great development has been much debated, however. A new discovery indicates we have been changing our surroundings with fire for at least 92,000 years.

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On arrival in new lands, humans have used fire to change them to suit their needs. “Firestick farming”  transformed the landscape of Australia and North America, creating environments better suited to hunting and reducing the chance of devastatingly large conflagrations. Anthropologists are seeking to determine when this early technology was mastered, and in particular, whether it preceded humanity's expansion out of Africa.

The difficulty in resolving this question is that thousands of years later, the changes wrought by human fires look similar to those started by lightning. However, Yale's Dr Jessica Thompson has found a distinctive signal in sediments around the edge of Lake Malawi, one of the largest lakes in Africa.

Over a 600,000 year period, these sediments reveal changes in the abundance and diversity of pollen as nearby plant life shifted with changing climate. Around 92,000 years ago, Thompson found an increase in charcoal deposition, indicating more frequent fires in the lake's catchment area.

Such a change could have several causes, but Thompson reports in Science Advances it coincides with a decline in the richness of pollen. “Trees that indicate dense, structurally complex forest canopies are no longer common and are replaced by pollen from plants that deal well with frequent fire and disturbance,” Thompson said in a statement. More sediment was deposited around this time as well, along with more human-made artifacts. With highlands less covered by forests, heavy rains brought more dirt down with them, sometimes accompanied by the items our ancestors had shaped.

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What these changes did not coincide with was new climatic conditions. Lake Malawi has shrunk drastically during dry periods, but stayed high at this time.

During dry eras Lake Malawi shrunk to a small fraction of its current size, but that didn't happen around the time charcoal shot up in lake sediments, indicating the extra fire was not climate-induced. Image Credit: Jessia Thompson

"One way or another, it's caused by human activity," Thompson said. What we don't know was whether the changes were deliberate or not. Perhaps an increase in the density of human populations in the area meant more campfires, which in turn led to more escaping and setting nearby forests alight.

Nevertheless, the fire-users almost certainly benefited, creating an ecosystem more attractive to large prey.

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The timing of this development lines up fairly closely with the estimated dates at which Homo Sapiens left Africa. However, co-author Dr Alex Mackay of the University of Wollongong told IFLScience we don't know if the use of fire as a land management tool helped make this possible. “There is evidence the range of things humans were capable of doing expanded around 100,000 years ago.” Mackay told IFLScience. “We don't know whether or not this was the thing that made migration possible.”

This was certainly not humanity's first use of fire. Last week evidence was published of fire more than a million years ago in a South African cave that would have required humans to bring both spark and fuel. Homo Sapiens hadn't even evolved then. Moreover, our biology suggests ancestral species have been eating cooked food for around two million years.

This leaves a long gap between the use of fire for warmth and cooking to harnessing it to change surrounding ecosystems. Mackay told IFLScience humans may have been using fire to change the landscape much earlier. However, if this occurred in outside the great lakes region, for example in southern Africa, it might not have left behind a signal we can read. “Humans co-evolved with fauna in Africa and it is hard to disentangle human the human impact from the rest,” Mackay said.


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