What were the ancient societies of Amazonia like before the first European sailors clambered ashore in the mid-16th century carrying strange new diseases and the seeds of war and conquest? For years, archaeologists have dueled over different views. Initially, most saw the vast Amazon Basin–which sprawls across Brazil, Peru, and five other countries in South America – as home to sparse bands of pre-Columbian hunters and gatherers who preserved the region’s forests as wilderness. Then, archaeological discoveries in the 1990s revealed large villages and complex societies in eastern Amazonia, giving rise to the theory that prehistoric agriculturists had cleared and intensively managed forests across the Amazon Basin for thousands of years.

Much rides on this assessment. If the Amazon, with its great diversity of plant and animal life today, was once extensively cleared and supported a large population of prehistoric people, that bodes well for the forest’s powers of recovery. But if the region harbored only small, scattered populations, then today’s ecosystem is truly virgin forest and perhaps very vulnerable to human activities.

A new study published online in Science, suggests that large ancient populations never cleared and tamed the western Amazon. By analyzing soil samples from 55 locations in central and western Amazonia, a team of American and Brazilian researchers led by paleoecologist Crystal McMichael, of the University of New Hampshire in Durham, have found that pre-Columbian bands ranged in small numbers over the region and gathered food without slashing, burning, or cultivating large tracts of the Amazon. “Most of the forest we sampled has never been intensively disturbed,” McMichael says.

McMichael and her colleagues journeyed by riverboat, small aircraft, and four-wheel-drive trucks across an area measuring 3 million square kilometers, taking soil cores from river bluffs close to known archaeological sites and from inland sites such as randomized localities along a transect from Porto Velho, Brazil, to Manaus, Peru. Back in the lab, McMichael analyzed each of the 247 cores to determine the abundance of charcoal, an indicator that humans set the forest ablaze to clear trees and enrich soils for crops, since natural fires are rare in Amazonia. In addition, archaeobotanist Dolores Piperno of the Smithsonian Institution National Museum of Natural History in Washington, extracted and identified phytoliths – characteristic microscopic silica fossils that are produced by many plant species and that trap minute amounts of carbon. Then the investigators sent samples of the charcoal and phytoliths out for radiocarbon dating.

The results took the team by surprise. “If humans were in those areas, they didn’t stay very long, and they didn’t farm,” says Piperno.

Moreover, this picture of small groups of hunters and gatherers in the western Amazon seems to fit with some data concerning ancient agriculture in the region. Before the arrival of Europeans, Amazonia’s inhabitants had only stone axes at their disposal, and clearing large rainforest tracts with such tools would have been enormously time-consuming. A study conducted in the 1970s, for example, showed that a worker equipped with a stone ax needed 115 hours to cut down just one tree.