We think of the Amazon rainforest as being untouched by humans, a wilderness of trees and bio-diversity. New archaeological and agricultural evidence is revealing this may be a myth.
It is estimated that up to 20 million people once lived in the Amazon but the population collapsed following the arrival of Europeans in 1492.
Diseases unknown in the Americas were introduced and it is thought that 90% of the indigenous population in some areas died as a result. They had no immunity.
More native people, both in North and South America, died from disease than in all the subsequent wars. 
Prior to this population collapse, many parts of the Amazon were probably as cultivated as regions in Europe. More than 200 species of trees are considered “hyperdominant” because they make up about half of the trees found in the rainforest. But many of these trees were probably cultivated on purpose.
It has implications for how much carbon the rainforests can absorb. All the tests  have been done in these relatively young areas of rainforest, which absorb much greater amounts of carbon. But this is not representative of the forest as a whole.