According to a new study led by Patrick Roberts of the University of Oxford, UK, early human foragers relied primarily on rainforest resources from at least 20,000 years ago.
Mountain forest in Sri Lanka. Image credit: Faslan / CC BY-SA 3.0.
The study, published in the journal Science, analyzed the carbon and oxygen isotopes in the teeth of 26 individuals, with the oldest dating back 20,000 years. All the teeth suggested a diet largely sourced from the rainforest.
Previously it was thought that humans did not occupy tropical forests for any length of time until 12,000 years after that date, and that the tropical forests were largely pristine, human-free environments until 8,000 years ago.
“The isotopic methodology applied in our study has already been successfully used to study how primates, including African great apes, adapt to their forest environment,” said study senior author Prof Julia Lee-Thorp, also of the University of Oxford.
“However, this is the first time scientists have investigated ancient human fossils in a tropical forest context to see how our earliest ancestors survived in such a habitat.”
Prof Lee-Thorp, Patrick Roberts and their colleagues studied the fossilized teeth of 26 humans of a range of dates – from 20,000 to 3,000 years ago. All of the teeth were excavated from three archaeological sites in Sri Lanka, which are today surrounded by either dense rainforest or more open terrain.
The analysis of the teeth showed that all of the humans had a diet sourced from slightly open intermediate rainforest environments.
Only two of them showed a recognizable signature of a diet found in open grassland. However, these two teeth were dated to around 3,000 years, when agriculture developed in the region.
“This is the first study to directly test how much early human forest foragers depended on the rainforest for their diet,” Roberts said.
“The results are significant in showing that early humans in Sri Lanka were able to live almost entirely on food found in the rainforest without the need to move into other environments.”
“Our earliest human ancestors were clearly able to successfully adapt to different extreme environments.”
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Patrick Roberts et al. Direct evidence for human reliance on rainforest resources in late Pleistocene Sri Lanka. Science, vol. 347, no. 6227, pp. 1246-1249; doi: 10.1126/science.aaa1230
