For years, it was assumed that humans were nothing but bad news for the Amazon rainforest. Our ancestors were believed to have kicked things off by clearing large patches for agriculture and construction, and we continue to do so today (along with a hearty helping of man-made climate change). According to researchers from the University of Reading, that couldn’t be further from the truth: The expansive, lush rainforest we know today only got that way due to climate change some 2,000 years ago.

“Our findings have serious implications for understanding past climate change, and how the Amazon basin might react to more modern forest clearance. It suggests that Amazonia was neither pristine wilderness, nor has it shown resilience to large-scale deforestation by humans in the past,” said Dr John Carson, a University of Reading paleoecologist who led the study.

Rather than a pristine, untouched forest slowly defiled by humans, the findings suggest that conditions were… kind of the opposite, actually. Prior to the transition to a warmer, wetter climate between 0-300 AD, much of what is now the southern Amazon was once fertile, open grassland – ideal for agriculture and constructing the large earthworks that have since been consumed by the jungle.

Ancient people just weren’t contributing much to deforestation, because until very recently, they simply didn’t need to.

“These results were very surprising. We went to Bolivia hoping to find evidence of the kinds of crops being grown by ancient Amerindian groups, and to try to find how much impact they had on the ancient forest. What we found was that they were having virtually no effect on the forest, in terms of past deforestation, because it didn’t exist there until much later,” said Carson.

It appears the most early peoples did was to suppress forest growth as it threatened to overtake their lands, and that ended around 1500 AD, when most of indigenous populations had been eradicated. With the effects of man-made climate change becoming more evident each day, scientists hope this glimpse into the Amazon’s past will help predict how it will respond to climate change in the future.