The Indus Civilization stretched over a million square kilometers of what is now Pakistan and India in the Third Millennium B.C. While contemporaneous civilizations in Egypt and Mesopotomia are well-known, their Indus trading partners have remained more of a mystery.
Lead author Gwen Robbins Schug, from Appalachian State University, said that the collapse of the Indus Civilization and the reorganization of its human population has been controversial for a long time.
Climate, economic, and social changes all played a role in the process of urbanization and collapse, but little was known about how these changes affected the human population.
Schug and an international team of researchers examined evidence for trauma and infectious disease in the human skeletal remains from three burial areas at Harappa, one of the largest cities in the Indus Civilization.
The results of their analysis counter longstanding claims that the Indus civilization developed as a peaceful, cooperative, and egalitarian state-level society, without social differentiation, hierarchy, or differences in access to basic resources.
The data suggest instead that some communities at Harappa faced more significant impacts than others from climate and socio-economic strains, particularly the socially disadvantaged or marginalized communities who are most vulnerable to violence and disease.
This pattern is expected in strongly socially differentiated, hierarchical but weakly controlled societies facing resource stress.
When paleoclimate, archaeology, and human skeletal biology approaches are combined, scientists can glean important insights from the past, addressing long-standing and socially relevant questions.
Schug said that rapid climate change events have wide-ranging impacts on human communities and scientists cannot make assumptions that climate changes will always equate to violence and disease.
"However, in this case, it appears that the rapid urbanization process in Indus cities, and the increasingly large amount of culture contact, brought new challenges to the human population. Infectious diseases like leprosy and tuberculosis were probably transmitted across an interaction sphere that spanned Middle and South Asia," she said.
Schug's research shows that leprosy appeared at Harappa during the urban phase of the Indus Civilization and its prevalence significantly increased through time. New diseases, such as tuberculosis, also appear in the Late Harappan or post-urban phase burials.
Violent injury such as cranial trauma also increases through time, a finding that is remarkable, she said, given that evidence for violence is very rare in prehistoric South Asian sites generally.
As the environment changed, the exchange network became increasingly incoherent and when you combine that with social changes and this particular cultural context, it all worked together to create a situation that became untenable, she said.
The study is published in the journal PLOS ONE.