Scientists have discovered the direct chemical traces of plant-based poison on stone arrowheads dating to roughly 60,000 years ago in South Africa. The findings provide evidence that early human hunters during the Pleistocene epoch used toxic plant extracts to enhance their hunting weaponry. The research was published in the journal Science Advances.
During the Middle Stone Age, hunter-gatherer populations living in the grassland and savanna regions of what is now KwaZulu-Natal relied on sharp stone tools to secure meat. Umhlatuzana Rock Shelter, an archaeological site in this area, holds layered deposits that record tens of thousands of years of human habitation. The people of this era produced tiny, deliberately shaped stone blades known as backed microliths, which they regularly affixed to wooden shafts.
These tools belong to a phase of rapid prehistoric innovation known as the Howiesons Poort technological tradition. Identifying exactly how these diminutive weapons functioned in prehistoric hunting presents a persistent challenge in archaeology. Organic materials like wood, plant fibers, and toxins generally decay long before modern excavation, leaving behind only the durable stone components.
Prior discoveries confirmed the use of poisoned arrows in Egypt and South Africa between 4,000 and 6,700 years ago, with scattered indirect clues pointing to earlier periods. A gap existed in the prehistoric record regarding exactly when humans first harnessed chemical toxins to hunt wild game. Some scholars suggested that the small microliths found in older sedimentary layers functioned as poisoned arrow tips because their size alone would not cause enough physical trauma to kill large prey. Until now, direct chemical proof of poison on Pleistocene weaponry remained absent from the scientific record.
Sven Isaksson of the Archaeological Research Laboratory at Stockholm University led the investigation alongside Anders Högberg of Linnaeus University and Marlize Lombard of the University of Johannesburg. The team focused on ten small quartz microliths excavated from a specific sedimentary layer at Umhlatuzana Rock Shelter. To determine the age of this layer, previous site investigators used a method called optically stimulated luminescence dating. This technique measures the last time individual quartz grains in the soil were exposed to sunlight, establishing that the surrounding sediment is approximately 60,000 years old.
The researchers used an analytical technique called gas chromatography-mass spectrometry to evaluate microscopic residues clinging to the unsharpened edges of the stone tools. This process separates a complex chemical mixture into its individual parts by turning the residue into a gas and pushing it through a microscopic tube. A detector then identifies the individual molecules based on their exact weight and atomic structure, allowing the team to spot specific organic signatures that survive in the archaeological record. They compared the chemical patterns found on the prehistoric quartz fragments with samples taken from 250-year-old poisoned bone arrows stored in museum collections, while also analyzing fresh toxic sap extracted from modern Boophone disticha reference plants.
The chemical analysis identified distinct traces of toxic plant compounds on half of the ten analyzed arrowheads. Specifically, the researchers found two naturally occurring poisons, buphanidrine and epibuphanisine. These compounds belong to a class of nitrogen-rich chemicals called alkaloids, which often have powerful physiological effects on humans and animals. While these alkaloids occur in several southern African Amaryllidaceae species, the only well-documented source used as an arrow poison is the bulb of a plant known locally as the poison bulb, or Boophone disticha, a species that has grown in southern African environments for millions of years.
Scientists note that these chemical compounds survived for tens of thousands of years because they possess rigid molecular structures and dissolve poorly in water. The presence of these alkaloids inside the ancient adhesive used to bind the stone blade to its shaft suggests the hunters mixed the poison directly into the glue or applied it thickly just behind the sharp cutting edge. The milky sap inside the poison bulb causes severe internal trauma and respiratory paralysis if it enters the bloodstream. Microscopic wear patterns on the quartz fragments show impact damage consistent with being shot from a bow and snapping off inside the hide of a target.
Using this specific chemical toxin indicates that these early human populations possessed advanced knowledge of local plant biology and animal behavior. Hunting with slow-acting poisons relies on persistence, as hunters shoot an animal and then track it over long distances while the toxin takes effect. The hunters understood that the poison bulb exudate functioned inside the animal’s body to weaken it over time. This long-range hunting strategy points to high levels of cognitive planning, abstract reasoning, and the ability to anticipate delayed outcomes.
Identifying complex biological compounds from the distant past involves significant analytical challenges. Environmental conditions must align perfectly to prevent total decay, and the slightly acidic soils of the Pleistocene layers at Umhlatuzana Rock Shelter provided rare preservation conditions for these organic residues. The small sample size of just ten analyzed quartz pieces limits broad generalizations about how frequently the broader regional population used poisoned weapons. The exact recipe the ancient hunters used to prepare the toxin remains unknown, as the sap could have been dried in the sun, boiled over a fire, or mixed with other organic binding agents that completely degraded over time. The absence of preserved wooden shafts or bows leaves open questions regarding the exact mechanical engineering of the complete Pleistocene weapon systems.
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.