Scientists have identified traces of a toxic plant extract on small stone arrowheads dating back 60,000 years in southern Africa. The discovery reveals that mid-Pleistocene hunter-gatherers utilized poisonous botanical compounds to enhance their hunting weapons long before previously documented. The findings were recently published in the journal Science Advances.
During the mid-Pleistocene epoch, roughly 60,000 years ago, communities of hunter-gatherers lived in the Umhlatuzana Rock Shelter located in present-day KwaZulu-Natal, South Africa. These early humans inhabited a landscape characterized by a mix of open grasslands and wooded savannas. Securing meat in this environment required advanced survival strategies and specialized tools that went beyond simple wooden spears or sharpened bones.
Before this investigation, direct chemical proof of poisoned hunting weapons dated mostly to the last few thousand years. Well-preserved bone-tipped arrows containing toxic residues have been found in Egyptian tombs dating back about 4,000 years. Similar finds from caves in South Africa provided evidence of poison use from about 6,700 years ago.
Finding proof from older periods remained an elusive challenge in human history. A few older artifacts showed signs of toxic substances, ranging from a debated wooden applicator to a lump of beeswax. Confirming the widespread use of plant poisons on ancient arrow tips from tens of thousands of years ago was difficult.
The severe lack of preserved organic material from the Pleistocene epoch created a significant historical gap regarding when humans first weaponized plant chemistry. Most organic matter tends to decay over such vast stretches of time, leaving only stone tools for archaeologists to interpret. Identifying invisible chemical traces on these stones provides a rare glimpse into ancient survival tactics.
Sven Isaksson, an environmental archaeologist at Stockholm University, led the investigation into these ancient tools. Isaksson collaborated with Anders Högberg of Linnaeus University and Marlize Lombard from the University of Johannesburg to examine small stone artifacts known as backed microliths. These tiny, precisely shaped pieces of quartz were crafted by early humans to serve as the piercing tips or cutting side blades of small projectiles.
The researchers focused their attention on a specific collection of microliths recovered from a 60,000-year-old sediment layer at the Umhlatuzana site. To preserve the rare artifacts for future study, the team employed a minimally destructive sampling approach. They specifically selected exactly 10 of these quartz microliths out of the hundreds that had been excavated from the rock shelter.
To find the invisible traces of poison, the team used an analytical technique called gas chromatography combined with mass spectrometry. This process involves safely dissolving microscopic amounts of the residue found on the stone and heating the sample until it becomes a gas. The scientific instruments then separate the different molecules passing through a tube and identify them based on their unique weights and structures.
To verify their results, the team also tested four ethnohistorical poisoned bone arrowheads collected in South Africa during the early 1770s by European travelers. They compared the chemical signatures obtained from the ancient stones and the historical bone arrows with modern sap. This modern sap was taken directly from poisonous plant bulbs growing in the local region today.
The chemical analysis revealed traces of two specific toxic compounds, buphanidrine and epibuphanisine, on five of the ten sampled quartz microliths. These complex molecular compounds belong to a class of naturally occurring organic chemicals called alkaloids. In southern Africa, these specific alkaloids originate almost exclusively from the bulb sap of a locally abundant plant known as Boophone disticha.
This particular plant has a long history of being used as an arrow poison by indigenous hunters. The chemical structure of buphanidrine makes it highly resistant to breaking down in the natural environment. Its low solubility in water and rigid molecular shape likely helped these microscopic chemical traces survive on the buried stone tools for 60,000 years.
The toxic residue was located along the blunt, shaped back of the stone tips. This placement suggests that the poison was mixed directly into the sticky adhesive used to attach the stone tips to wooden or bone weapon shafts. Traces of plant oils and fatty acids were also detected on the tools, which points to a complex adhesive recipe that combined toxic plant sap with a separate binding agent.
Microscopic impact scars and scratch marks on the sharp edges of the stones provide evidence that these weapons experienced forceful collisions. The damage patterns indicate that the stones were mounted sideways on the weapon shafts to create a wide cutting edge. This specific design and wear pattern aligns heavily with how much later hunter-gatherers engineered their poison arrow tips.
Finding this exact plant extract on hunting weapons yields deep insight into how these early communities secured their food. Because this specific plant poison targets the nervous system and does not kill animals instantly, hunters likely shot their prey and then tracked the weakened animal over long distances. This delayed approach to hunting suggests that these early humans possessed a comprehensive understanding of animal behavior and regional ecology.
The ability to identify, extract, and safely process a highly toxic plant bulb indicates advanced procedural knowledge among these early humans. Using a chemical substance to achieve a delayed, invisible result requires abstract thinking and complex spatial planning. The evidence suggests that mid-Pleistocene communities in southern Africa had already developed sophisticated cognitive abilities and actively passed down specialized botanical knowledge through countless generations.
Despite these successful chemical detections, studying organic residues from 60,000 years ago presents severe preservation challenges. Plant materials and natural adhesives degrade completely over time, especially in shifting climates and varied soil conditions. The deep sediments at the Umhlatuzana Rock Shelter shift from acidic to alkaline across different layers, a process that can rapidly destroy delicate organic molecules.
The researchers noted that small-scale sediment mixing by burrowing animals or deep plant roots makes finding perfectly intact organic traces extremely difficult. Occasional moisture variations within the ancient cave floor also threaten the long-term preservation of chemical residues. The team targeted artifacts from the deepest, dryest sediment layers to maximize their chances of finding surviving poison components.
There is also no direct fossilized plant evidence proving that this specific poisonous bulb grew in the immediate vicinity of the rock shelter during that exact climatic period. Scientists rely entirely on the plant’s long evolutionary history in the region and its hardiness in dry savanna environments to infer its local availability. The bulb is known to survive extreme droughts and fires, classifying it as a reliable, long-lasting resource on the landscape.
Several questions remain regarding the exact mechanical engineering of these ancient weapons. Modern and historical poisoned arrows are often designed with tips that intentionally break loose inside the animal, allowing the poison to enter the bloodstream while the hunter retrieves the main arrow shaft. It is still unknown if the Pleistocene inhabitants of the Umhlatuzana Rock Shelter engineered their arrows with this same advanced detachable mechanism.
Future archaeological digs in the region may focus on uncovering intact weapon shafts associated with these tiny stone tips. Additional chemical testing on other tool types could reveal if this toxic plant sap was used exclusively for hunting or if it served medicinal purposes in smaller doses. Clarifying these details will help archaeologists map the full extent of human technological progress during the mid-Pleistocene.
The paper, “Direct evidence for poison use on microlithic arrowheads in Southern Africa at 60,000 years ago,” was authored by Sven Isaksson, Anders Högberg, and Marlize Lombard.