Since the 1960s, conservationists have had a standard solution for saving biodiversity: Protect natural areas from human influence. But a new analysis of Earth’s land use going back 12,000 years suggests that even in the time of mammoths and giant sloths, just one-quarter of the planet was untouched by humans, compared with 19% today. Because some of those inhabited areas are now biodiversity hot spots, people probably helped sustain—and even increase—the diversity of other species for millennia, the authors write. The findings also suggest many traditional practices and Indigenous peoples play a key role in preserving biodiversity.
The paper “debunks an important myth” in conservation circles, says Massachusetts Institute of Technology aerospace engineer Danielle Wood, who studies technology and international development but was not involved with the new work. By offering a long-term look at humans’ impact on the planet, the study reveals that it’s not people per se that send biodiversity on a downward spiral, but it’s instead the overexploitation of resources, she explains. If their practices are sustainable, “humans don’t have to be removed,” to save the world’s species.
To find out how human habitation has impacted biodiversity, a multidisciplinary team of researchers from several universities refined a model for predicting past land use. The model starts with maps of current land use patterns—the locations of rangelands, agricultural lands, cities, and mines—and incorporates census data about past and present population sizes. It then works backward, adding archaeological data to predict land use at 60 points in time over the past 12,000 years. On the resulting maps, the researchers overlay current data about vertebrate biodiversity, threatened species, and protected areas, as well as government-recognized Indigenous areas.
They found that humans had spread across almost three-quarters of Earth, excluding Antarctica, by 12,000 years ago, occupying great swaths of what conservationists now call “natural,” “intact,” or “wild” lands. Ten thousand years ago, the true extent of such untouched lands was 27%; now, it is 19%, the researchers report today in the Proceedings of the National Academy of Sciences. But even more provocatively, the team found statistical associations between current biodiversity hot spots and past land use suggesting that ancient people played a role in preserving, or even creating, these hot spots, including the Amazon and the Congo.
The results “illustrate the fallacy of the concept of ‘pristine’ nature untouched by human hands,” says Ruth DeFries, a sustainability scientist at Columbia University who was not involved with the study.
Yet they also show some recent dramatic changes. For example, land use remained fairly stable for much of the past 12,000 years, but began to shift radically from the 1800s through about 1950. Those changes include the familiar modern threats of intensive agriculture, urbanization, large-scale mining, and deforestation.
The findings come as no surprise to anthropologists and archaeologists, who know that humans have been managing natural landscapes for millennia—by burning forests and planting fields, for example. But the paper “adds to a growing cry by some rights groups and conservation organizations that Indigenous communities should be in control of biodiversity hot spots,” says Dana Lepofsky, an archaeologist and ethnoecologist at Simon Fraser University. Fiore Longo, head of the conservation campaign for the Indigenous rights group Survival International, agrees. “This paper confirms what we’ve been saying for years,” she says. “Wilderness is a colonial and racist myth with no basis in science,” that has often been used to justify the theft of Indigenous lands.
Anthropologists note that not every Indigenous group in history has sustained biodiversity. Ancient people likely helped drive to extinction megafauna like mammoths and flightless Pacific island birds, for example. But, “There is no question [that] Indigenous people have been much better stewards of nature than the rest of us,” says Eric Dinerstein, a conservation biologist at the Washington, D.C., sustainability nonprofit RESOLVE. “The single most important thing we can do is empower and finance Indigenous peoples to conserve their sovereign lands.”