Prehistoric hunters may have tipped their stone arrows and spears with poisons to help them bring down prey, scientists believe. Researchers have developed a new technique that allows them to test ancient weapons for residues left by toxic plant material added to them. Preliminary tests have suggested that a set of 4,000-year-old stone-tipped arrows from Egypt were coated with poisonous compounds including the plant Acokanthera. Dr Valentina Borgia, a specialist in paleolithic hunting weapons at the McDonald Institute for Archaeological Research at the University of Cambridge, believes hunters may have been using toxic chemicals on their weapons up to 30,000 years ago. The image above shows arrows from China that were used in a crossbow that were dipped in poison . She said that Paleolithic hunters may have used poisonous pastes made from plants to help make their weapons kill prey more swiftly. Early humans may have evolved to throw spears allowing them to hunt around two million years ago, a new study has suggested. Scientists have found that the skeletons of early species of human changed to give them the ability to throw much like modern humans. A study of fossils of Homo erectus, an extinct human ancestor, shows that their shoulders and collar bone would have allowed them to hurl sticks accurately and powerfully. This would have enabled Homo erectus to become a proficient hunter, able to throw weapons like spears and rocks at potential prey. She said: 'It made good sense for people to use poisons. 'On their own, Palaeolithic weapons with stone arrowheads may not have been deadly enough to immobilise or kill a large animal such as a red deer. 'Poisonous plants were plentiful and the prehistoric population knew the environment where they lived, they knew the edible plants and their potential as medicines and poisons. 'To fabricate a poison is easy and economic, and the risk is minimal. In addition, the making of poisons is often part of the tradition and the rituality of hunting.' Dr Borgia has been working with forensic scientist Michell Cralin from Northumbria University and Dr Huw Barton, from the University of Leicester, to test for the presence of poisonous plants on prehistoric weapons. Using a technique called liquid chromatography mass spectrometry, which is used to detect traces of drugs by modern forensic scientists, they are examining residues left on the tips of ancient weapons. They are also looking for the presence of starch grains that may have been left on the weapons from toxic plant material. This wooden spatula from Malaysia wrapped in a palm leaf was used to apply poison to darts used for hunting . Dr Borgia has conducted tests on 4,000 year old arrow heads found in Egypt (left) that are thought to have been tipped with a poisonous black residue. The image on the right shows a pot of curare, a plant-based poison which is still used by some indigenous hunter-gatherers in South America to coat darts and arrows . They can then compare the results from these tests against a database of known poisonous plants. Dr Borgia has already collected samples from a number objects known to have contained poison and ancient weapons to test the technique. These include a 1926 Chinese pot containing Aconite poison inside, Malaysian darts tipped with the poison Upas, Chinese crossbow arrows and a number of African arrows. Many hunter gatherer societies are known to use poisons when they are hunting. The Yanomami people in the Amazon rainforest use curare - a mix of bark scrapings from Strychnos vines - to tip their darts and arrows when hunting. The use of curare was once common among indigenous populations in South America. The researchers have used starch grains like the ones shown on the left from the plant Aconitum napellus  to help identify poisonous materials. Aconitum was found inside this pot on the right thought to date from 1926 . In Africa hunters use another species of Strychnos to produce the poison strychnine, while other plants like Acokanthera, and Strophantus are also used. Hunters in Northern Asia are also known to have used monkshood to kill large animals such as bears and Siberian ibex. The seeds from yew trees are also thought to have been used to poison arrows. Dr Borgia has also collected black residue from six arrows that date from pre-dynasty Egypt. These 4,000-year-old arrows were first studied by scientists 40 years ago when small portons of the residue from the stone tips were injected into a cat. Opium, magic mushrooms and other psychoactive drugs have been used by humans for thousands of years. An anthropologist has discovered that humans have been cultivating and using mood-altering substances since the Stone Age. Professor Elisa Guerra-Doce has compiled evidence from around the world that Neolithic people were taking drugs derived from cacti in 8,600BC and that they were cultivating opium poppies by around 6000BC. Researchers have also found reddish stains on 13,000 year old human teeth found in a burial pit in Duyong Cave on Palawan Island in the southern Philippines, which are thought to be caused by chewing the leaves of the betel plant. It is still chewed through out much of Asia as a mild stimulant. Charred cannabis seeds have also been found in bowls that date from the Bronze age Pit-Grave culture that appeared in Romania around 2000BC. This bone harpoon in a museum in Cambridge carries a warning label that reads 'Care, Has been poisoned' The animal did not die but became ill, suggesting the presence of a poison. Dr Borgia said: 'Nowadays we have the right instruments to get more information without cruelty to animals. 'Initial tests strongly suggest the presence of Acokanthera, a poisonous plant on our database, but we can’t be completely certain as there are a number of components in the compound. 'We know that the Babylonians, Greeks and Romans used plant-based poisons both for hunting animals and in war. 'In fact, the word ‘toxic’ come from toxon, the Greek for bow. Taxus is a genus of the yew tree with a springy timber traditionally used to make bows. 'It also produces seeds used to poison arrows. In Britain, yews grown for their timber were planted in churchyards so that animals wouldn’t be poisoned by eating their berries. “Few hunter-gatherer societies remain today but all the groups that have survived employ poisons.'
Scientists at Cambridge University are testing ancient weapons for poisons . They believe paleolithic hunters  used plant toxins up to 30,000 years ago . This would have made stone tipped spears and arrows more lethal to prey . Early tests on 4,000-year-old arrows from Egypt have shown signs of toxin . The team now hope to test the tips of older weapons for signs of poison .