In 1983, in the Kruger cave (northeast of South Africa), researchers detected, among the numerous artifacts collected, a rather unusual antelope femur. Dated 7,000 years ago, it contained three bone arrowheads and the remains of a mysterious toxic substance.
His recent chemical analysis, the results of which are published in the journal Science and featured in The Conversation on January 23, 2025, revealed a complex mixture of plant-based poisons. This is the oldest confirmed evidence of such a mixture applied to arrows, testifying to the cognitive abilities and pharmacological knowledge of the ancient populations at its origin.
7,000 year old poison recipe
From 2022, new archaeological investigations will be carried out in the Kruger cave, in the Magaliesberg mountains. The scientists then decided to also re-examine the organic materials which had been taken there forty years earlier, in particular the famous femur, of which the x-ray images taken in the past were of “relatively poor quality”indicates in The Conversation Justin Bradfield, archaeologist associate professor at the University of Johannesburg, author of the new research.
Modern micro-computed tomography (micro-CT) confirmed that the bone contained arrowheads, as well as foreign material. Analysis of its chemical components revealed the presence of two glycosides: digitoxin and strophanthidin.
Historically, these toxic substances have been used in bowhunting poisons, due to their disruptive effect on heart muscle function. Ricinoleic acid has also been identified, which is formed when ricin, a highly toxic substance in castor beans (Common tick), decomposes under the influence of oxygen.
All of these organic compounds, as well as others identified, do not come from the same plants. This suggests that several plant ingredients were combined to create this poisonous recipe. Furthermore, no species containing digitoxin or strophanthidin grows naturally in the vicinity of Kruger Cave. 7,000 years ago, its operators therefore had to travel long distances to acquire these ingredients or exchange them. Well before this period, the transport of marine shells, used as ornaments and then as currency, was already practiced throughout Africa.
-The fact that people knew what plants to acquire, where to find them, and how to use them effectively speaks volumes about the antiquity of traditional pharmacological knowledge systems. – Justin Bradfield
Innovation among the first hunters
This is by no means the oldest use of poison for hunting, recalls the specialist. Historical records show that, in most parts of the world, hunters used toxic compounds derived from plants and animals to make their weapons more effective. The oldest molecular evidence of the use of poison in southern Africa was thus unearthed in the Border Cave (border between Eswatini and South Africa): traces of ricinoleic acid on a wooden spatula, dating back 24,000 years.
However, this latest poison appears to have only been composed of a single ingredient. “Our discovery is the oldest confirmed evidence of a mixture of two or more plant toxins applied specifically to arrowheads”note le Pr Justin Bradfield.
In addition to directly testifying to the cognitive abilities of these ancient craftsmen, this study highlights “the potential contribution ofarchaeobotany (the study of ancient plant remains) and organic chemistry to understanding the past”adds the archaeologist. “It shows how these two disciplines can work together to tell the story of our ancestors.”
