In a groundbreaking study published in Nature Ecology and Evolution, an international team of researchers unveils compelling evidence that human populations inhabiting the tropical rainforests of Sri Lanka intensified their consumption of plant resources thousands of years before the advent of agriculture. This revelation challenges conventional narratives of agricultural origins and delivers fresh insights into the complex subsistence strategies employed by prehistoric communities navigating dense rainforest ecosystems.
The research focuses on a comprehensive analysis of human and faunal remains dating from approximately 20,000 to 3,000 years ago, spanning the Late Pleistocene into the Holocene epoch. Employing sophisticated zinc stable isotope (δ⁶⁶Zn) analysis on tooth enamel, the team was able to reconstruct the dietary compositions and relative trophic levels of individuals within this ancient ecological framework. Zinc isotope analysis offers an exceptional window into dietary habits, especially within challenging tropical contexts where traditional organic residue preservation is poor or absent.
Zinc isotopes serve as a sensitive bioarchaeological tool due to their ability to reflect trophic level shifts: higher δ⁶⁶Zn values typically correlate with increased plant consumption, while lower values indicate greater reliance on animal protein. By analyzing enamel samples from 24 human individuals alongside 57 faunal specimens from the region, the researchers discerned consistent omnivory but with a nuanced and progressive incline toward heightened plant ingestion over millennia. This subtle yet profound dietary transition precedes any confirmed evidence for domesticated crops, refuting models that posit a swift agricultural revolution.
The discovery hinges on meticulous study of key cave sites such as Fa-Hien Lena, Batadomba-lena, and Balangoda Kuragala, locales rich with tens of thousands of years of archaeological deposits indicating sustained human habitation. Previously, the emphasis on hunting was largely due to the durability and abundance of faunal remains and lithic hunting tools. However, organic plant materials typically do not withstand tropical decay processes—rendering direct identification of plant use exceedingly difficult. This study’s application of δ⁶⁶Zn analysis fills that critical evidentiary gap and brings plant consumption to the forefront.
According to Dr. Nicolas Bourgon, the study’s lead author and postdoctoral researcher at the Max Planck Institute of Geoanthropology, the data indicate that these rainforest inhabitants were intensifying their plant resource use long before the emergence of agriculture. Rather than abrupt shifts coinciding with domestication, plant exploitation followed a protracted trajectory—signaling adaptive flexibility and deep ecological knowledge. This suggests that early foragers were actively modifying their subsistence strategies, perhaps cultivating wild stands or managing plants in a proto-agricultural manner.
The implications of this research extend beyond Sri Lanka, contributing to a broader paradigm shift in understanding how tropical rainforests were engaged by prehistoric humans. Often considered ecological barriers to prolonged human occupation, these environments are now revealed as dynamic arenas where populations developed complex and sustainable resource management techniques. The findings lend support to models that envision the origins of agriculture as incremental processes emerging from long-term foraging innovations, rather than sudden revolutions in subsistence.
State-of-the-art zinc isotope measurements were conducted using a Thermo Scientific Neptune Multi-Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS). This high-precision instrumentation allows for discerning subtle isotopic differences in mineralized tissues, critical for reconstructing paleodiets in tropical contexts overwhelmed by moisture and microbial degradation. By targeting the bioapatite within tooth enamel—a tissue that resists diagenesis—the researchers ensured the reliability of dietary proxies over extensive temporal spans.
The study highlights how integrating geochemical techniques with archaeological contexts enhances our understanding of human-environment interactions deep in prehistory. While traditional archaeobotanical approaches often struggle in humid tropical sites due to poor preservation of organics, isotopic proxies offer a robust alternative for reconstructing ancient diets and subsistence dynamics. The zinc isotope data articulate an ongoing intensification of plant consumption that aligns with environmental and cultural transformations observed in the archaeological record.
Dr. Oshan Wedage from the University of Sri Jayewardenepura, co-author of the study, emphasizes the importance of local adaptations; these rainforest groups were not passive occupants but active agents shaping their ecological niches. Their dietary flexibility and management practices challenge simplistic dichotomies between hunter-gatherers and early farmers, revealing instead a spectrum of subsistence behaviors finely attuned to tropical rainforest resources.
Professor Patrick Roberts from the Max Planck Institute further contextualizes the discoveries, noting that these findings add to mounting evidence that tropical rainforests were crucibles for human innovation, not impediments. The slow and steady intensification of plant use documented here aligns with models of niche construction theory, wherein humans actively modify ecosystems to enhance resource availability long before the formalization of agricultural systems.
This study’s methodological advancements and profound implications encourage reevaluation of prehistoric diets in other tropical regions globally. The nuanced shifts in trophic positions recorded through zinc isotope signatures challenge us to reconsider how early humans engaged with plant foods, underlining the complexity of dietary evolution and the protracted gestation of agriculture from deep-rooted foraging traditions.
Ultimately, these insights forge a deeper appreciation for the intricate balance prehistoric tropical foragers struck between animal and plant resources. Rather than sudden agricultural revolutions, the evidence paints a picture of gradual, multi-millennial processes underpinning subsistence intensification, shedding light on human resilience and ingenuity amid some of the world’s most biodiverse and challenging environments.
Subject of Research: People
Article Title: Pre-agricultural intensification of plant use in Pleistocene Sri Lankan rainforests
News Publication Date: 20-May-2026
Web References: 10.1038/s41559-026-03082-6
Image Credits: Max Planck Institute of Evolutionary Anthropology
Keywords: zinc isotope analysis, δ⁶⁶Zn, Pleistocene, Holocene, tropical rainforest, Sri Lanka, pre-agriculture, trophic level, stable isotopes, human diet, archaeology, foraging, subsistence strategies
