Fires naturally shape ecosystems. They can clear land of trees, recycle nutrients from dead vegetation back into the soil and provide conditions for seeds to germinate. According to new research conducted in the East African Rift Valley – the cradle of modern humans – our ancestors likely knew at least some of this and learned to manipulate ecosystems to their advantage.
The research was led by Jessica Thompson, professor of anthropology at Yale University. Her team has been excavating early-human sites in the valley that date to around 315,000–30,000 years ago. They’ve recovered more than 45,000 stone artifacts. In order to link their finds with the environmental record, they also measured the levels and varieties of charcoal along the northern shores of Lake Malawi, together with the species richness of fossilised pollen in the lake’s sediments. What they found was a clear spike in charcoal levels around 85,000 years ago. The spike coincided with a shift in pollen away from forest species and towards the vegetation more commonly seen in open bush and grasslands. After ruling out tectonic and climatic factors as explanations for these patterns, they concluded that early humans must have modified dense forest environments at this time, transforming them into the open grasslands and bush that dominate the area around Lake Malawi today. Given the presence of charcoal, they must have done it with fire, around eight times earlier than the world’s first land transformations through agriculture.
This isn’t the first time that a seismic shift in the environmental record has been attributed to ancient humans. A study published in the journal Nature in 2017 used a similar approach to demonstrate that, not long after they arrived in Australia from Asia via a land bridge around 50,000 years ago, humans caused the extinction of Australia’s megafauna, almost certainly through overhunting. ‘Early people, over a long period of time, took control over their environment rather than being controlled by it,’ says Thompson. ‘We have a long history of changing environments.’ She points to research led by a colleague, Erle Ellis from the University of Maryland, which shows that for the past 12,000 years, nearly three quarters of the Earth’s land has been inhabited and shaped by human societies, including more than 95 per cent of temperate forests and 90 per cent of tropical forests.
There are diverse, culturally significant reasons for the use of fire for environmental manipulation by 21st century humans. Many groups clear and manage landscapes by deliberately igniting fires, often to create pastureland for livestock. But research shows that the environmental impacts of anthropogenic fires is likely to worsen as a result of climate change, due to altered rainfall patterns that lead to drier, more fire-prone conditions, and higher temperatures.
Brazil’s Pantanal Wetlands have perhaps experienced the most notorious of anthropogenic, environmentally-damaging fires of the 21st century. By December 2020, fires had consumed nearly 4.5 million hectares of the Pantanal, 22 times the area of wetland lost between 2000 and 2018. IBAMA – Brazil’s environment watchdog – say 98 per cent of the 22,000 fires ignited in 2020 were manmade, mostly to clear pastureland for livestock. Nearly 30 per cent of the Pantanal biome has been affected. Lighting such fires may be an ancient, natural human practice, but Thompson cautions us not to view it in this way, given how extreme modern-day land-use change has become.
‘It’s tempting to read these kinds of studies and say, “Maybe something that makes us human is to have control over the world around us.” But that doesn’t provide moral justification for the scale at which we’re doing it now. There isn’t a single environment that you could call untouched or pristine. But the way we now influence land through mechanised practices, fire regimes and industrial-scale operations is vastly different from any point in our history.’