Why do estimates of the preconquest Indigenous population of South America vary so widely?

Estimates of the preconquest Indigenous population of South America vary widely due to the challenges of reconstructing demographic data from the period before European contact. Because no comprehensive census existed at the time, scholars must rely on indirect evidence, which often leads to significant discrepancies in their findings.12

The primary reasons for these varying estimates include:

• Methodological Differences: Researchers use different models to calculate population density based on the carrying capacity of specific culture areas. Small changes in initial assumptions—such as the ratio of warriors to the total population or the number of dependents per household—can result in vastly different final figures when extrapolated over time.2
• Impact of Disease: There is ongoing debate regarding the timing and severity of epidemic diseases. Some scholars argue that introduced pathogens caused catastrophic mortality rates as high as 95 percent, while others question the assumptions used to calculate these losses from later, more reliable records.23
• Interpretation of Historical Accounts: Early colonial records often focused on military or labor potential, frequently neglecting to document the size of the general population, which forces historians to make subjective estimations.2

While some older estimates for the Americas combined were as high as 100 million, more recent, conservative assessments suggest a preconquest population for South America of approximately 20 million.1