DNA recovered from ancient mummies in Chile has provided the firmest scientific evidence to date that European colonization introduced smallpox to the Americas, according to a study published Thursday in the journal Science.
Researchers identified smallpox infections in the ancient DNA of an adult man and woman whose remains were found at an archaeological site in Camarones, located in northern Chile. By analyzing the genes and dating the remains, scientists determined the two individuals likely died between 1492 and 1631.
Genetic Links to Europe
The study, led by geneticist Shigeki Nakagome of Trinity College Dublin, involved the examination of 13 bone samples. The evidence of infection was found specifically in leg bone fragments.
To determine the origin of the virus, researchers compared the genetic sequences from the Chilean remains to other known versions of the disease. They found that the strains infecting the individuals in the Americas fit neatly between European strains from the medieval period and later versions. This molecular evidence suggests the virus evolved from European strains before spreading through the Americas.
Nobody would ever question that smallpox came to this hemisphere from colonization, but this proves it,
said Patricia Foster, a biologist at Indiana University who was not involved in the research.
Pathways of Infection
While the genetic link to Europe is clear, the study authors noted that the exact population that brought the virus to the Americas remains unclear. Possible pathways include:
- Waves of European settlers following the 1492 Caribbean explorations of Christopher Columbus and the South American coastal explorations of Amerigo Vespucci roughly a decade later.
- The introduction and expansion of the slave trade, which could have passed the disease through Africa.
The discovery is particularly significant because the infections were found in an area with no previous record of the disease. This raises new questions about how the virus reached such remote southern populations, with researchers suggesting it may have spread via Indigenous trading networks that existed before Europeans arrived.
Human and Demographic Cost
The research also highlights the biological toll of the pandemic. The two individuals identified with the virus were between 18 and 35 years old, and scientists believe the disease is likely what killed them.
Before its eradication in 1980 through vaccination, smallpox was one of the deadliest diseases in history, killing approximately one-third of those it infected and leaving survivors with deep, disfiguring scars. In the Americas, the virus devastated Indigenous populations who had no prior exposure.
Constanza de la Fuente Castro, a biological anthropologist at the University of Chile and study coauthor, stated that the findings demonstrate how the disease wiped out entire populations, leaving them vulnerable to European conquest. It wasn’t just cultural or demographic. It’s literally written into biological evidence that we can still recover and read today,
de la Fuente Castro said.
Viral Evolution
Beyond confirming the history of the disease, the analysis of various strains allowed scientists to observe how the virus evolved over time. The study found that the virus became more effective at its deadly mission by turning off certain genes.
