̽��ֱ�� of Cambridge - forensic

Poisons, plants and Palaeolithic hunters

amb206 — Sat, 21 Mar 2015 10:30:00 +0000

We’re surrounded by poisonous plants: they thrive in our parks and gardens, hedgerows and woodlands. Foxgloves (Digitalis) look charming but their seeds can kill. ̽��ֱ��flowers of monkshood (Aconitum napellus) are a stunning blue but its roots can be deadly. Hemlock (Conium maculatum) is both common and extremely toxic as Shakespeare reminds us in Macbeth with the incantations of the witches.

Archaeologists have long believed that our ancestors used poisons extracted from such plants to make their weapons more lethal and kill their prey more swiftly. By dipping an arrow head into a poisonous paste, the hunter could ensure that an animal would receive a dose of toxic chemicals - alkaloids or cardenolides - that would either kill it immediately or slow it down.

Until very recently it has been impossible to prove that poisons extracted from plants were used by early societies. Now Dr Valentina Borgia, a specialist in Palaeolithic hunting weapons and Marie Curie Fellow at the McDonald Institute for Archaeological Research, believes that she is on the brink of being able to prove that our ancestors used poisons as far back as 30,000 years ago.

Borgia has approached the likely use of poisons by our distant ancestors from a number of viewpoints. Her research looks at the ubiquity of poisonous plants in many local environments and their use both historically and by modern hunter-gatherers. Working with a forensic chemist she has also developed techniques capable of detecting tiny residues of poison on archaeological objects. She is now putting those techniques to the test with samples obtained from museum collections.

“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,” says Borgia.

“Few hunter-gatherer societies remain today but all the groups that have survived employ poisons. ̽��ֱ��Yanomami people of the Amazonian rainforest use curare - a mix of Strychnos genus plants - to poison their arrows. In Africa, a variety of different plants are used to make poisons. Acokanthera, Strophantus and Strychnos are the most common.”

Many Northern Asian populations used monkshood (Aconitum) to kill large animals such as bear and Siberian ibex. Poisonous plants also feature in folklore. In Malaysia, darts are poisoned using Antiaris toxicaria, a poison that comes from the Upas tree. A Malaysian legend says: “Seven up, eight down and nine no life”. ̽��ֱ��victim takes seven steps uphill, eight steps downhill and a ninth final step.

In 2014, Borgia enlisted the expertise of forensic chemist Michelle Carlin (Northumbria ̽��ֱ��) to help her devise a method for identifying residues of poison. Carlin’s day-to-day work is focused on crime and the detection of illegal substances through chemical analysis. Using a highly specialist technique called liquid chromatography-mass spectrometry, she is able to detect invisible traces of drugs – such as cocaine in pocket linings.

̽��ֱ��same technique can be used to detect the presence of poisons used thousands of years ago. Together Borgia and Carlin have created a database listing toxic plants and have developed a non-destructive method of collecting samples of residues from archaeological materials, by simply touching the item with cotton imbued with pure water.

Samples of poisonous plants were supplied to the researchers by the Botanic Garden at the ̽��ֱ�� of Cambridge and Alnwick Castle in Northumberland. Alnwick has a Poison Garden where visitors can see 150 poisonous plants. Some (such as monkshood) are so toxic that Alnwick has to obtain a licence from the Home Office in order to cultivate them.

Another route to identification of plant residues is to look for the presence of starches which remain on the surface of the prehistoric weapons. Starch grains can be used to determine plant taxa: each species has distinctive size, shape and structure. Borgia has collaborated with a major expert in this methodology, Dr Huw Barton ( ̽��ֱ�� of Leicester) in order to use starching testing as one of her research tools.

Many museums with ethnographical collections have poisoned weapons in their displays and stores. Borgia has been able to collect samples from objects held by the Museum of Archaeology and Anthropology in Cambridge, the Pitts Rivers Museum in Oxford and the Museo Etnografico Pigorini of Roma (Italy) with the collaboration of her Italian colleague, Dr Jacopo Crezzini. ̽��ֱ��objects include a Chinese pot with Aconite poison inside (wrapped in a newspaper dated 13 July 1926), Malaysian darts poisoned with Upas, various African arrows and a glass tube containing curare.

“ ̽��ֱ��wonderful craftsmanship used to create objects so strongly associated with poison is also significant. As the French philosopher Simondon says, there is no pure technical device free from symbolic meaning,” says Borgia. “These artefacts fully express this concept, as they show a high degree of care. A scary-looking Borneo harpoon, wonderfully carved, in the Cambridge museum is thought to have been made from a human bone. A card, conserved with it, warns ‘Care. Has been poisoned’.”

Carlin’s analysis of these samples of materials has shown that residues of poisons are easily detectable on the objects a century later and that the residues retained their chemical characteristics. Now the real challenge for the researchers is to go much further back in time.

Testing of a sample of six stone-tipped pre-dynastic Egyptian arrows, dating from 4,000 years BC and conserved in the Phoebe A Hearst Museum of Berkeley (USA), is now taking place. At the time these arrows where first studied, 40 years ago, the researchers removed small portions of the black residue present on the tips, and injected into a cat. ̽��ֱ��reaction of the poor animal (which did survive) was evidence of the presence of a poison on the arrows.

“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,” said Borgia.

“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. Poisons 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.”

When archaeologists remove items from the ground in the course of field work, they brush off the soil adhering to the finds and sometimes even wash objects. Borgia is appealing to fellow archaeologists to contact her when they find weapons and not to clean up their finds. “Now we have this technique available, and have shown that it works, we need to test it as much as possible on archaeological samples,” she says.

Borgia denies that her family name (Lucrezia Borgia is legendary as a devious poisoner) prompted her interest in poisons but she delights in the Latin quip ‘nomen omen’. It translates roughly as ‘significant name’ and certainly the name Borgia has powerful historic resonances. Luckily for Borgia’s colleagues, her objectives are honourable and entirely academic.

She says: “Investigation of the use of poisons in Prehistoric periods adds to our understanding of hunting techniques and rituals, and also how the plant world was exploited. ̽��ֱ��Renaissance physician Paracelsus wrote that dosis facit venenum (the dose makes the poison). Ethnographic studies tell us that the most common toxic plants used in poisons were also used to treat diseases. Not surprisingly, the same substances are the basis for many medications still in use today.”

Inset images: Aconitum napellus, credit Wikimedia Commons; starches of Aconite; pot of Aconitum wrapped in the 1926 newspaper, copyright of Museum of Archaeology and Anthropology, Cambridge; Egyptian arrow with poison, copyright of Phoebe A Hearst Museum of Berkeley (USA); poisoned arrows for crossbow, China, copyright of Museum of Archaeology and Anthropology, Cambridge; pot of curare, Peru, copyright of Pitt Rivers Museum, ̽��ֱ�� of Oxford.

Dozens of common plants are toxic. Archaeologists have long suspected that our Palaeolithic ancestors used plant poisons to make their hunting weapons more lethal. Now Dr Valentina Borgia has teamed up with a forensic chemist to develop a technique for detecting residues of deadly substances on archaeological objects.

Spatula to poison darts, Malaysia

̽��ֱ��text in this work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page. For image rights, please see the credits associated with each individual image.

Yes

Can a voice identify a criminal?

tdk25 — Sat, 01 Sep 2007 00:00:00 +0000

Recognising a voice is a familiar experience for most people – identifying a friend’s voice over the telephone, recognising the voice of a well-known personality on the radio, hearing the voice of a colleague call out from behind. But why do voices sound distinctive? Given our ability to recognise individuals, it seems reasonable to assume that voices are unique, but it has not been scientifically demonstrated that all voices are measurably distinctive. In spite of the impression given by televised crime shows, as yet there is no technique available to identify a speaker with 100% reliability.

This is a serious problem for forensic speaker identification, a branch of forensic phonetics in which a phonetician is asked to identify an unknown speaker whose voice has been recorded during the committing of a crime, for example a bomb threat, ransom demand, hoax emergency call or drug deal. ̽��ֱ��phonetician compares the incriminating recording with samples of speech from a suspect with a view to identifying the perpetrator or eliminating the suspect. These cases are often controversial, and since the extent to which an individual’s voice is idiosyncratic has not yet been established, research in this area is crucial.

A key problem in attempting to characterise a speaker is that each individual’s voice can vary greatly. We change our voices depending on who we are talking to, how formal the situation is, the emotion we wish to express and whether there is background noise. Speakers’ voices also change if they are tired, drunk or have a cold or sore throat, and of course speakers can disguise their voices. So a voice is much more complicated to capture than a fingerprint, which is a fixed, unchanging feature of an individual.

DyViS: investigating speech

A team of researchers in the Department of Linguistics – Dr Kirsty McDougall, Dr Gea de Jong, Toby Hudson and Professor Francis Nolan – is carrying out innovative research in speaker identification in the DyViS project (Dynamic Variability in Speech: A Forensic Phonetic Study of British English), funded by the Economic and Social Research Council (ESRC).

To investigate the problem of variation within a speaker’s voice, the DyViS team have compiled a large-scale database of recordings of southern British English spoken across a range of speaking styles. Speakers participated in several tasks: a mock police interview where they were required to ‘lie’ about a particular scenario, a telephone call with a friend involving a more casual and relaxed style of speech, and a number of reading tasks. All of the speaking tasks included a particular selection of words that the participants had to utter in different contexts. These data enable the researchers to investigate how phonetic features of these words change for a given individual across the different speaking styles, and to what extent these features can be used to distinguish individuals.

Identifying the speaker

One particular feature being examined is a phenomenon known as ‘formant frequency dynamics’. Formant frequencies are the resonances of the vocal tract during speech – the frequencies at which vibrations of air are at maximum amplitude in the vocal tract in speech sounds such as vowels. Formant frequencies appear as roughly horizontal dark bands on a spectrogram, a computer-generated representation of the acoustic speech signal. These frequencies are powerful cues to speaker identity since they are determined by both the physical dimensions of a speaker’s vocal tract and the way the speaker configures the vocal organs to produce each sound.

Previous research on speaker differences has typically measured the formant frequencies only at the centre of the sound. ̽��ֱ��DyViS research goes beyond these ‘static’ measures to investigate the dynamics of formant frequencies, which reflect the movement of a person’s speech organs and are likely to reveal more fine-grained differences among speakers. Just as people exhibit personal styles for walking, running and other skilled motor activities, they move their vocal organs in individual ways when producing speech.

Dr McDougall’s experiments have investigated the speaker-distinguishing potential of the formant frequency dynamics of the vowel sound in spoken words like bike and hike, of the vowel sound in who’d, and of sequences containing an ‘r’ sound preceded and followed by vowel sounds such as a route and a rack. ̽��ֱ��work shows that formant frequency dynamics carry considerable speaker-specific information. By taking measurements along the formant contours surrounding the centre of a speech sound, a significant improvement in speaker discrimination is achieved.

Forensic phonetics

Together with research into other features of speech being investigated by the DyViS team, this work offers crucial new directions for solutions to the problem of extracting a speaker’s ‘signature’ from the speech signal. Findings from the DyViS project suggest that dynamic features of speech could provide a clue in speaker identification, which has clear applications in forensic evidence – in comparing voices and speech for purposes of identification, and in analysing speech recordings.

̽��ֱ��research also has important implications for phonetic theory. Current models of speech production and perception do not provide a good explanation of the role of individual variation in speech communication. ̽��ֱ��analysis of dynamic features of speech being undertaken by the DyViS team will lead to important theoretical developments in these areas, contributing to our understanding of how individual speakers can communicate with the same language yet sound so different from each other.

Innovative research in the Department of Linguistics suggests that dynamic features of speech could provide a clue to forensic speaker identification.

Travis Isaacs from Flickr

Ear

This work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page.

Yes