By Ashley Strickland, CNN
(CNN) — Scientists have detected traces of plant toxins on Stone Age arrowheads that were used by hunter-gatherers in South Africa about 60,000 years ago.
The find marks the oldest known poison arrows and indicates that such tools and sophisticated hunting strategies existed thousands of years early than previously thought, according to the authors of a study published Wednesday in the journal Science Advances.
“In persistence hunting, poisoned arrows did not usually kill prey instantly,” said lead study author Sven Isaksson, professor of archaeological science at Stockholm University’s Archaeological Research Laboratory. “Instead, the poison helped hunters reduce the time and energy needed to track and exhaust a wounded animal.”
Two different alkaloids, or organic plant compounds, found in the poisonous chemical residue were from the gifbol plant, or Boophone disticha. Traditional hunters in the region still utilize the plant today and refer to it locally as poison bulb.
Hunter-gatherers likely dipped the quartz arrowheads, excavated from the Umhlatuzana Rock Shelter in KwaZulu-Natal, South Africa, in 1985, in poison before using them to kill animals for food. The presence of poison arrows during the Late Pleistocene suggests that hunter-gatherers knew which plants to use, as well as how long it would take for the toxins to be effective.
“Understanding that a substance applied to an arrow will weaken an animal hours later requires cause-and-effect thinking and the ability to anticipate delayed results,” Isaksson wrote in an email. “The evidence points to prehistoric humans having advanced cognitive abilities, complex cultural knowledge, and well-developed hunting practices.”
Identifying a poisonous plant
While humans have long relied on plants as food, poison arrows are just one example of how our ancestors living during the the most recent ice age exploited the chemical properties of plants to develop medicine and toxic substances, Isaksson said.
Hunters could have applied poison to the points, also called backed microliths, by stabbing the gifbol plant’s bulb, or by cutting the bulb and capturing the poisonous substance in a container. The poison may have been concentrated by applying heat or exposing it to sunlight, according to the study.
Poisons work in different ways, with some varieties like myotoxins destroying muscle tissue and others, called neurotoxins, attacking the nervous system. Hunter-gatherers may have avoided any part of the animal affected by myotoxins, whereas neurotoxins would be diluted after spreading throughout the animal’s body, Isaksson said.
“Some toxins are only dangerous if they enter the blood stream and are not harmful when ingested,” he said via email. “Others may be easily destroyed by heat and thus neutralized by cooking.”
Chemical analyses showed the presence of the alkaloids buphandrine and epibuphanisine on five of the 10 quartz arrowheads. Despite being buried for thousands of years, the arrowheads still retained residue because the alkaloids have specific chemical characteristics that enabled them to endure, like the fact that they don’t dissolve easily in water.
Even small quantities of the plant’s toxins can be lethal to rodents within 20 to 30 minutes and can cause nausea, respiratory paralysis, edema of the lung, feeble pulse and other symptoms in humans, according to the study.
For comparison, the authors also examined four 250-year-old arrowheads collected in South Africa and brought to Sweden. The analysis found that their points were laced with the same toxic alkaloids, suggesting the long history of traditional use of the poison in hunting, the authors said.
“Finding traces of the same poison on both prehistoric and histor