Isotopes in tooth and bone
In the dense rainforests of Sri Lanka, archaeological sites like Batadomba-lena and Fa-Hien Lena hold the remains of anatomically modern humans who lived as far back as 48,000 years ago. For a long time, tropical rainforests were considered difficult environments for early hunter-gatherers. The story of "Balangoda Man," a name given to these prehistoric people, changes that perspective. The primary evidence comes from stable isotope analysis of their skeletal remains.
Scientists analyzed the carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes in tooth enamel from individuals dating back tens of thousands of years. These chemical signatures are a permanent record of diet. The results showed consistently low δ¹³C values, which shows a diet sourced from a closed-canopy rainforest. Foods from open grasslands or marine environments produce distinctly different, higher isotopic signatures. This proves these early Sri Lankans were not occasional visitors to the forest but were highly specialized, full-time rainforest dwellers. This dedicated rainforest adaptation is one of the earliest examples found for Homo sapiens anywhere in the world.
A prehistoric rainforest menu
The isotopic data is strongly supported by the animal bones and plant remains found in the same cave deposits. The diet of Balangoda Man was a broad-spectrum one, focused on the consistent capture of small and agile prey. Zooarchaeological evidence shows a heavy reliance on semi-arboreal and arboreal animals. Frequent remains include monkeys, giant squirrels, and porcupines. Hunting these animals in the dense forest required a specialized toolkit.
Archaeologists have found an abundance of geometric microliths—small, precisely shaped stone tools made from quartz—dating back as far as 48,000 years at Fa-Hien Lena. These small points were likely used as tips for arrows or darts, essential technology for hunting in a complex, three-dimensional forest environment. The diet also included freshwater snails, notably of the genus Acavus, and plant foods like wild breadfruit and kekuna nuts. This evidence shows a stable and successful adaptation to the Sri Lankan rainforest that lasted for tens of thousands of years.