A woman on a boat on the Tupana river, Brasil. Photo: Stephanie Morcinek/Unsplash
- Scientists are rethinking humanity’s role in shaping the planet – from a mostly recent phenomenon to an ancient and widespread force.
- Most landscapes considered “natural” have long histories of human use, and truly pristine ecosystems have been rare for millennia.
- This revelation – which aligns with many forms of Indigenous knowledge – can be both enlightening and disorienting for those of us raised in Western cultures.
The Brazil nut is a wondrous thing. The tree can grow more than 150 feet tall – a titan even by Amazonian standards – and may live to 1,000 years. Giant bees pollinate its plump yellow flowers, and the softball-sized fruits take longer than a human foetus to mature. Each woody sphere contains dozens of the oblong seeds you find in a can of mixed nuts.
To sprout into a new tree, the seeds require help from animals like agoutis – long-legged relatives of guinea pigs. They gnaw open the fruit’s hard shell, eat what they like and bury the rest, the way squirrels accidentally plant acorns.
But rodents alone may not explain how the Brazil nut became one of the most common trees in the Amazon. Humans probably helped too. People appear to have spread and nurtured the Brazil nut, as well as other plants like cacao trees and edible palms. They likely dispersed seeds and hacked back competitors, which helps explain why useful species make up some 84% of all the trees and palms in the Amazon.
This history is well known to many Indigenous residents of the region, who carry on similar practices today. But Western scientists and writers often missed it. They saw the Amazon as a wild jungle in which humans could eke out a living, but just barely. Only recently have outsiders learned to recognize the intimate connection between people and the forest, says Carolina Levis, a historical ecologist at Universidade Federal de Santa Catarina in Florianópolis, Brazil, who works closely with forest residents. “It’s impossible to separate these two components of the Amazon.”
Indeed, Levis and other ecologists now classify many parts of the Amazon as domesticated forest.
It’s just one example of how scientists are rethinking humanity’s role in shaping the planet – from a mostly recent phenomenon to an ancient and widespread force. As a recent study in PNAS details, people have inhabited roughly three-quarters of Earth’s land area for at least 12,000 years and left their mark wherever they went. Even most landscapes considered “natural” have long histories of human use, and truly pristine ecosystems have been rare for millennia. “We fail to appreciate that humans have been all over the place,” says study coauthor Nicole Boivin, an archaeologist at the Max Planck Institute for the Science of Human History in Jena, Germany.
This revelation – which aligns with many forms of Indigenous knowledge – can be both enlightening and disorienting for those of us raised in Western cultures that draw a hard line between humans and nature. It challenges the idea of human influence as overwhelmingly harmful, as it often appears under the pall of a changing climate and collapsing biodiversity, and forces us to confront a much more complex reality. “When you learn this stuff, suddenly you just look at everything differently,” Boivin says.
But should our long legacy of ecological meddling make us think less of nature – or more of humans?
Early humans’ impact
If you ask Erle Ellis what people tend to get wrong about humanity’s relationship to nature, he says it starts with the myth that “there can be people not shaping nature.” Ellis is an environmental scientist and geographer at the University of Maryland, Baltimore County, who led the new PNAS study and authored a history of human land use published in the 2021 Annual Review of Environment and Resources.
Homo sapiens evolved about 300,000 years ago from a line of hominins that had already learned to make tools and control fire, and they took these skills on the road as they spread around the world. In many places, people burned the landscape to improve hunting grounds or to boost populations of favored plants, shifting the balance between forests and grasslands in the process.
Humans also became formidable hunters. Even the biggest animals on Earth found themselves unprepared to fend off this new upright predator. Between about 50,000 and 7,000 years ago, most of the world’s megafauna went extinct, including a half-ton thunderbird that once roamed Australia and a giant ground sloth known as Megatherium, or Great Beast, native to South America.
Most scientists now agree that people played at least some part in many of those extinctions. And that implicates us in the massive environmental shifts that followed, which have started to receive more attention.
Large herbivores, like elephants and their extinct counterparts, knock down trees and munch on seedlings, creating open habitat. They graze on grass, reducing the fuel available for wildfires. And they eat fruits and nuts, dispersing seeds far and wide when they poop. Large meat-eaters also affect ecosystems by preying on herbivores and keeping them on the move.
It now appears that the disappearance of these beasts upended ancient landscapes, expanding forests and, in some places, increasing the frequency of fires. It likely affected the water cycle, the carbon cycle and even the color of the planet as dark trees replaced lighter vegetation, according to an overview published in the Annual Review of Environment and Resources. The extinctions also took out countless parasites, scavengers and dung beetles that made a living off megafauna.
And that was just the beginning. Humans decimated many other species and drove evolutionary shifts in those that survived. Studies suggest that over the course of millennia, harvesting pressure shrank the size of saltwater snails, desert tortoises, and Himalayan lotus flowers. (Modern examples of human-induced evolution include tuskless elephants that don’t attract ivory poachers and short-winged swallows that can better avoid cars.)
But that’s not the whole story. Other species, like the Brazil nut, benefited from human interventions and migrations. People introduced the common cuscus – a marsupial native to New Guinea – to various Pacific islands more than 20,000 years ago and, more recently, helped spread the now-ubiquitous coconut palm across the Indian and Pacific oceans. With the rise of agriculture, people cleared forests to make way for farms and created entirely new varieties of crops and weeds, livestock and pests.
As societies proliferated and diversified, people created ecosystems unlike any that came before. They sprang up in patchwork landscapes of small settlements and cultivated fields set among grasslands and forests. Such “mosaics” offer a range of habitats and so tend to support many kinds of plants and animals. (Today, industrialized agriculture and forestry usually do the opposite, creating large, uniform landscapes.)
These strange, new ecosystems became much of what we now call nature, including some of the world’s biological crown jewels: the forests of southeast Asia, the grasslands of Africa, and of course, the Amazon. According to the PNAS study, three quarters of the places recognized as Key Biodiversity Areas by the International Union for Conservation of Nature have been used by humans for at least 10,000 years, and many are still home to Indigenous and other local peoples today. That suggests these landscapes exist at least in part because of human actions – not simply in spite of them.
It also means the ongoing loss of biodiversity can’t be explained primarily by the destruction of “untouched” wildlands (though, for myriad reasons, those remain important to preserve). Rather, Ellis and his colleagues argue, it’s a consequence of new intense and destructive ways of using the planet.
Also read: The Idea of Arid Lands as ‘Wastelands’ Comes Mostly From Colonial Assumptions
The myth of pristine nature
By now, a large body of research supports the idea that widespread human influence dates back long before the Industrial Revolution. But the implications are still sinking in, Boivin says. In ecology, for example, they demand a revolution of sorts – from seeing human-altered landscapes as “substandard” to deeming them worthy of study and protection, she says. “This is just something that people are coming to grips with.”
Humanity’s long history of modifying the planet also complicates efforts to study modern environmental impacts. Historically, scientists often assumed that ecosystems existed in a pristine state when Western researchers first encountered them. They then use that initial contact as a baseline against which to measure recent shifts. But mounting evidence, including a new assessment of pollen records published in Science, illustrates the problem with that approach.
The results show accelerating changes in global vegetation patterns starting around 4,000 years ago, likely as a result of human actions. That means ecologists studying modern changes are not spotting the first signs of human influence, but merely the latest ones, says Suzette Flantua, a coauthor of the study and a global change ecologist at the University of Bergen in Norway. “We’re saying, ‘Well, actually, you are seeing the tip of the iceberg,’” she says.
This context matters for things like climate change. In the Amazon, for instance, some researchers have warned that studies may overestimate the forest’s capacity to absorb planet-warming carbon by failing to account for how it could still be responding to the collapse of a large Indigenous population ravaged by European diseases and colonial oppression. Researchers have cited similar concerns in the Arctic, where it’s unclear whether ongoing changes in tree and shrub cover stem solely from warming, or also from the legacies of past human actions like hunting, reindeer herding and burning.
Humanity’s long environmental history also complicates the debate over whether we now live in the Anthropocene – a proposed new geologic epoch defined by human influence – and if so, when it began. Many scientists have converged on a start date in the mid-1900s, when human impacts overwhelmed natural processes (the waterline, in Flantua’s iceberg analogy). But others say that the Anthropocene should encompass the whole iceberg, including the end of the megafauna and the rise of agriculture. Still others take issue with the whole idea of enshrining an era of human dominance, and of lumping all humans together as a single disruptive force.
At their core, these questions crash up against the stubborn myth of pristine nature that has dominated Western thought for centuries. It began with Enlightenment thinkers, who saw humans and nature as fundamentally separate, and gave rise to the idea of wilderness as a refuge from human society – not the product of it. In the United States, that philosophy was codified into law with the Wilderness Act of 1964, which sought to preserve “an area where the earth and its community of life are untrammeled by man, where man himself is a visitor who does not remain.”
The notion remains potent today. It’s why tourists flock to places like California’s Channel Islands National Park thinking it’s natural, says Jon Erlandson, an archaeologist and the director of the University of Oregon’s Museum of Natural and Cultural History. In reality, the Island Chumash people lived there for millennia and profoundly shaped the landscape before Europeans arrived bringing deadly epidemics and forcibly removing the survivors to mainland missions in the 1800s. (In recent years, Chumash people have again traveled to the islands on traditional plank canoes.)
Over thousands of years, the Chumash likely used fire to expand the grasslands where they harvested edible bulbs – which remain a dominant feature of the islands today. They hunted sea otters and abalone, and introduced foxes, possibly also mice and skunks. After the Chumash were gone, more than a century of ranching further transformed the landscape that draws people today. “The islands they are visiting are fantastic. They’re wonderful. They’re scenic,” Erlandson says. “But they’re not wilderness.”
Learning from Indigenous peoples
Over the past few centuries, the agricultural and industrial revolutions – and an economic order premised on growth – have transformed Earth’s surface, altered the planet’s climate, and pushed us to the brink of another mass extinction. Today, it’s easy to see the fingerprints of modern humans all over the planet. Nuclear waste festers beneath the Greenland ice sheet and trash has found its way to the bottom of the Mariana Trench, the deepest spot in the Pacific.
Governments and environmental groups often try to tackle these problems by protecting nature from people. But that can be a terrible mistake, according to a group of researchers led by Michael-Shawn Fletcher, a geographer at the University of Melbourne and a descendant of the Wiradjuri people who live in eastern Australia.
The impulse to conserve wilderness has been used to justify evicting or marginalizing Indigenous and traditional people who have managed landscapes sustainably for thousands of years, and often harms the very ecosystems such efforts aim to protect, Fletcher and his colleagues wrote in a recent perspective in PNAS. The researchers describe wilderness itself as “an inappropriate and dehumanising construct.”
Indigenous peoples inhabit many of the forests and grasslands that host much of the world’s remaining biodiversity. And Indigenous leaders have long championed their communities’ deep ecological knowledge and success as environmental stewards and protectors. “We have this strong relationship with the land,” says Viviana Figueroa, a member of the Omaguaca people of northwest Argentina and a lawyer who works on international Indigenous rights and biodiversity. “Just support us.”
A growing body of research backs this view. Studies show that, in many places, Indigenous lands host equal or higher levels of biodiversity than wilderness protection. A recent UN report found that Indigenous-held lands also experience less deforestation and store more carbon than surrounding areas.
Removing humans, on the other hand, can actually degrade ecosystems. In Australia, the removal of Aboriginal peoples in the 1960s may have contributed to a rise in uncontrolled wildfires and a rash of local extinctions. And in the Amazon, Levis and her colleagues estimate that, without human management, natural forces could reduce the abundance of edible species by up to 80%, which would impact animal food webs.
Also read: What are the Ambitions of Ecosystem Restoration?
Many Indigenous activists and environmental scholars argue that a better solution to our planetary woes involves empowering local people to manage and protect the ecosystems they are part of. Some countries and environmental groups have already started to create new kinds of conservation areas that honor both the natural and the cultural history of key places. And global leaders have begun to recognize the importance of traditional knowledge for meeting global climate and biodiversity goals.
Just as we need to put people back in natural landscapes, we might also consider putting nature back into landscapes altered by people. One example of this approach is “rewilding”, a movement to restore native animals and then let ecological forces take over, ideally without much intervention. Rewilding efforts have already reintroduced gray wolves to the western US, bison to Romania and small carnivorous marsupials called quolls to mainland Australia.
The idea fits into a new model of restoration that doesn’t seek to recreate past versions of nature, or even maintain any kind of fixed state at all. Especially in a changing climate, “that’s generally not going to be possible,” says Jens-Christian Svenning, a biologist at Aarhus University in Denmark. Svenning says we should instead focus on “providing conditions that promote biodiversity” – basically, giving nonhuman species the space and resources to weather inevitable changes, human-caused or not.
Cultivating this kind of wildness does not require wilderness, Svenning points out. “If you go out in your garden and stop manicuring it, then you have wildness.” And that can be valuable, he says, even if it’s not pristine.
This seems like both good practical and emotional advice for those of us struggling to make sense of a complicated past and to confront the planet’s daunting future. We cannot turn back the clock and live the way humans did thousands of years ago. There are too many of us that need food, housing and livelihoods, which will require people to use parts of the world in intensive ways. But perhaps we can still fumble forward, taking ownership of our role as a species that changes the planet, and caring for the wildness that persists in the world. That’s what humans – at our best – have been doing for a very long time.
This article originally appeared in Knowable Magazine, an independent journalistic endeavor from Annual Reviews.