Scientists studying the Amazon rain forest are tangled in a debate of nature versus nurture.

Many ecologists tend to think that before Europeans arrived in the Americas, the vast wilderness was pristine and untouched by humans. But several archaeologists argue that ancient civilizations once thrived in its thickets and played a role in its development.

Now, researchers have found evidence that indigenous people may have domesticated and cultivated Amazonian plants and trees thousands of years ago, further supporting the idea that ancient humans helped shape the forest.

“Large areas of the Amazon are less pristine than we may think,” said Hans ter Steege, a tropical ecologist at the Naturalis Biodiversity Center in the Netherlands, and an author of a paper published in Science on Thursday. “The people who lived there before Columbus left serious footprints that still persist in the composition as we see today.”

He was one of more than a hundred researchers who found that domesticated tree and palm species — like cacao, cashews, the açaí palm, the Brazil nut and rubber — were five times more likely to dominate the modern Amazonian forest than nondomesticated plants.