Knowing the peculiarities of species allows me to understand the assemblages of pollen grains retrieved from a soil sample in terms of habitats and ecosystems. It allows me to see the kind of place represented by the pollen and spores, and the greater the number of different taxa in the assemblage, the sharper will be the image. These are not simple processes; there is no step-by-step procedure to follow to lead you from a chaos of raw data to an absolute answer. With so many aspects to hold in mind, the best forensic ecologist must perform a kind of informed intuition.
As if to prove the point, in 2009 I arrived at the 30th anniversary conference of the Association for Environmental Archaeology in York. Here, environmental archaeologists from across the world gathered to do what scientists do at conferences like this – to pool expertise. By now it had been some years since I last worked in archaeology, but I had resolved, nevertheless, to deliver a paper and, taking the floor, I presented a spectrum of pollen taxa I had obtained from a forensic case. The results were from a case commissioned by the RSPCA against badger diggers. These men, who can only be considered to be cruel thugs, put their dogs down into setts to find badgers. Both animals invariably inflict horrendous injuries on one another; in ordinary circumstances, the dog would come off worse – except that, once located, the men simply dig out the hapless brocks and kill them. This is great sport, isn’t it? It is, of course, against the law in the UK, and in this particular case, the RSPCA was hoping to get a conviction to deter others.
I had been given soil-laden spades and samples from the top and centre of a badger sett, and then had to compare the palynomorph spectrum of the spades with those from the badgers’ home. Analysis showed that they matched well, but the cherry on the cake was finding a rare spore in both the crime scene soil and in the soil on the spades. This particular spore, so rare that neither I, nor Judy Webb, my colleague who is absolutely brilliant at identifying pollen, flies, and many other things, had seen it before. It was a turning point in both this case and, in fact, the course of my life. Not only did it become a key piece of evidence for the prosecution; it was how I got to know my new husband. I had not met him up to that point but I was lucky that, while I was in the throes of this case, I literally bumped into this lovely man at a memorial service for one of my dear botany teachers from King’s College, the renowned Francis Rose. The service was held at Wakehurst Place, the country establishment belonging to the Royal Botanic Gardens, Kew and, after the inevitable ceremonial tree-planting, this very well-dressed man and I were walking together towards tea and cake through the dappled light of the woodland when I spied through the trees what I thought was Russula emetica, a lovely red-capped fungus.
‘Oh yes,’ said my companion, ‘it’s Russula but not emetica, I think.’
‘Oh, you know about fungi?’ I asked.
‘Yes, a little,’ he said modestly.
That was of immediate interest to me as I desperately needed someone who could identify difficult fungal spores.
‘What is your name?’ I asked casually.
‘David Hawksworth.’ It slowly sunk in.
‘Not the David Hawksworth?’
I was shocked because in my mind this man should have been about 90. The work of this world-renowned mycologist had been in literature for years, and was certainly on my list of references for my students at King’s College, and at least two of his books were on my bookshelf. Yet here was a very interesting man of about my age, with twinkly eyes and a boyish grin. When I got back, I told Judy Webb about my chance meeting and she was excited. ‘Oh, Pat,’ she said, ‘you must cultivate him. He’ll be very useful to us.’ The rest is history and I married this clever, knowledgeable man three years later.
It was through David that we discovered that the weird spore from the badgers’ sett was from a fairly rare truffle which grows on the roots of oak trees. Like dogs and pigs, we learned from this case that badgers obviously love truffles. One could only suppose that they had foraged in the roots of the oak tree about 100 metres away and brought truffles back to the sett. There were the spores as testament and, my word, they endowed a rare and convincing component to the palynological profile. They were not found in any of the other samples, and the truffle gave the crime scene profile a distinctive identity. When the spores were also found on the spades, they provided evidence with much greater potency than the pollen alone had given.
At the archaeological conference, I presented the attendees with an assemblage of pollen from this case, dominated by oak, with some elm, maple, lime, hawthorn, ivy, and honeysuckle – along with some buttercups, foxgloves, grasses, docks, and ferns. I then asked them what kind of place they thought this was. A few hands were tentatively raised – no one wanted to look silly – but all those who called out said roughly the same thing. ‘It’s woodland,’ they said, ‘from the edge of a glade.’
This was a perfectly reasonable assumption – but it was also quite wrong. This was not woodland at all; these samples had been taken from open pasture, about 10m away from a very old hedge and 100m from an oak tree. The landscape as a whole had been open, but divided into neat fields, all bounded by mixed hedges. I had confirmed my long-held suspicion that many palynologists still know little about how pollen actually disperses across the ground in most habitats in spite of the heavy weight of literature about the phenomenon.
In the United Kingdom, historically, the countryside has been developed by different kinds of management and two distinct types are recognised. Counties like Essex, Sussex, and Suffolk have wood pasture (bocage) country. This is the classic, pretty, mixed arable and pastoral countryside of England, with small fields enclosed in species-rich hedges, with some standard trees. The other kind is fielden (champagne) country which, in the historic meaning, simply means a landscape of wide, open fields, where arable farming involved division of the land into strips, so typical of Lincolnshire, Leicestershire, Wiltshire, and many others.
All those daring to answer in that conference room had got it wrong. They had assumed woodland but, in actual fact, it had represented bocage country, with the ‘woodland’ pollen and spores coming from the hedgerows enclosing the fields. The herbs were survivors of grazing, or those growing in the shelter of the hedge boundary. This, of course, was the lesson I had learned in my first case with the police – and it is the sort of thing that constantly complicates assumptions. The palynologists in the room were absolutely gobsmacked that their interpretation was so far off. It also demonstrated the degree of cognitive bias that, through default, prevails in much thinking in environmental interpretation.
Every last one of the palynologists in that room had jumped to the kind of wrong conclusion that, in my own field of work, might have serious consequences for a victim of crime, or somebody accused. In forensics, the stakes are very different where people’s lives and freedoms matter. And that is why recreating possible landscapes from the palynomorphs deposited on clothes and shoes is not as straightforward as just tallying up the pollen taxa, spores, and other particulates left behind. One cannot just read the existing palynological literature and assume that a certain assemblage will represent a specific landscape. One cannot act like an automaton, using other people’s published interpretations each time; it would make pollen and spore interpretation equivalent to ‘painting by numbers’. Only by knowing about the natural world we live in, both on vast and microscopic scales, can we be confident of getting close to the truth.
There are no shortcuts to this kind of knowledge. It is the hard-won accomplishment of many years. This is not work for those with a limited attention span, or the easily distracted. I have already said that the painstaking business of counting and cataloguing every possible palynomorph salvaged from a piece of clothing or implement can run to hours, days, and weeks. Well, acquiring the broad interdisciplinary knowledge to be able to look at those findings, and have a feeling for the most likely possibilities for where something might have happened, or what a sequence of events might have been, tak
es much longer. This is a lifetime’s endeavour. But when the pieces fit, and an idea of what might have happened suggests itself, the sense of discovery, of a puzzle having been solved, can be immense.
When the girl staggered into her local police station, in the town on the edge of the North Wessex Downs, she was in obvious distress. Her face was smeared and red with tears, her eyes showed the telltale signs of panic and, when the police constable attending the desk escorted her into an interview room to determine the problem, the words came out in a rush. There was a place, only 100m from her home, she said, a place with trees and shrubs, a strip of land between two rows of houses. ‘He forced me down onto the ground and there were woodchips scattered around. He was wearing pyjama bottoms, with Snoopy on them, over his jeans.’
Sometime later, when I got the call from the police and was asked to attend the case, I heard as much of the story as they knew. The boy and girl had been out together and, on the way home in the dark, instead of leaving her at her gate, he had forced her on another 100m or so into this wooded strip of ground. He did not deny having sexual relations with her, but he did deny ever having been to the area she claimed it had happened. According to the accused, he and the girl had eagerly lain down together on the turf, in the darkness of the public park some 100m before they reached her home – and it was here that, according to him, they had had consensual sex. Thus, his alibi site and the putative crime scene were about 200m apart.
Before I was called, the medical examination of both parties had already been done. The police surgeon had taken swabs from both the alleged victim and the accused, searching for DNA evidence from the tip and shaft of his penis and by swabbing her vagina. The presence of his DNA did not help the police case, however, because the boy had already admitted having sexual intercourse with the girl. Cases like this are the bread and butter of what I do and have been ever since the early ‘who was telling the truth’ case back in Welwyn Garden City.
The scope of a forensic ecologist is wide. If a body is found in an overgrown ditch, I can be called in to examine the site and lay out the possibilities for how the killer may have approached and left the scene of the crime. If a body is found decomposed beyond recognition, we can estimate – sometimes with unnerving accuracy – the length of time that has elapsed between the victim’s murder and the discovery of their body. We can locate clandestine burials on small and large scales; we can analyse the contents of your gut to interpret the events that led up to your death; we can identify the residues of poisonous or psychoactive plant materials left behind in cups and other containers, but linking people and places is at the heart of what we do.
Perhaps, in this North Wessex case, I would not be able to confirm whether intercourse had been consensual or not, but by inspecting the biological trace evidence left in their clothing and footwear, I could probably throw light on where the putative rape had happened. This might tell whose story was false, and whose came more closely to the truth.
It was a golden day in June when I got out of the crime scene manager’s car in the North Wessex market town and, together, we made our way to the place where the girl claimed she had been raped. The patch of wooded land was much as she had described it in her statement to the police. The road running alongside it was bordered by a wide strip of herb-rich turf, neatly mown and planted with trees and shrubs. We walked along the path into the little strip of woodland and I immediately took in the large oak tree, as well as the silver birch and the elder bush that grew close to where she said the offence had happened. Under the oak, and immediately alongside the path linking the two rows of houses, was a bare area of scuffed, earthy ground, strewn with woodchips. Between the trees, wherever there was sufficient light, herbs were groping up towards the sky. The houses on the side of the entrance to the path had well-tended gardens, with golden Laburnum, early roses, specimen non-native trees, fruit trees, cypress, ivy, and more.
I wandered back to the alleged crime scene. Apart from the woody species, it did not look very promising to me, although I thought it might be richer in trace evidence than at first sight. For one thing it was untidy, with plenty of woody detritus from fallen twigs, and these were bearing mosses and lichens; there were also some etiolated male nettles near the base of the oak. If they had been here together, as the girl had said, they might both have picked up a wide and specific range of trace evidence types, both from this year and residual pollen and other palynomorphs from previous years.
There are few absolutes in biology. Everything is probabilistic whether it concerns human health, the composition of the flora in a rich pasture, the animal and plant species found in any pond, or the growth pattern of daisies in the lawn. The identity and quantity of the various kinds of pollen and spores found in a sample depends on a great many variables, which we call ‘taphonomic factors’. I define palynological taphonomy as ‘all the factors that determine whether a palynomorph will be found in a specific place at a specific time’. It’s something that you learn gradually and can never take for granted. It always depends on context and we have to consider its complexities whenever we are interpreting our findings as it is so easy to come to a wrong, potentially damning, conclusion.
Think of what you see in a sunbeam at home. The large numbers of tiny particles could be your own skin flakes, mites, tiny fragments of insects, plants, fungi, or even mineral soil. All these contribute to the ‘air spora’, a useful term describing all the pollen, spores, and other microscopic entities floating around in the air. Eventually, they fall as ‘pollen rain’, creating dust on your mantelpiece or sideboard.
Some plants rely on the wind to disperse their pollen or spores, while others have evolved ways of attracting insects (and even bats or birds) for pollination. Flowers attracting animals are often coloured, perfumed, and give nectar while some, which attract flies, even smell like dung. Wind-blown pollen may travel some distance from the parent plant and, because the process of wind pollination is hit and miss, vast amounts are produced by some species – these are the ones that invariably give us hay fever. Grasses, sedges, oak, hazel, and many others all fall into this group. The flowers are usually green, yellow, or brownish, and are insignificant-looking. Invariably, they are grouped into inflorescences at the end of stalks, and are like little lambs’ tails shaking their pollen into the breeze. Finding wind-blown pollen on, say, a murder suspect does not necessarily mean that particular plant was present at the crime scene because, depending on the lie of the land, and any barriers such as buildings and vegetation, it may fail to reach the site even though it is capable of travelling considerable distances. A wall or tree trunk can provide a formidable barrier to pollen dispersal.
Just think of the way hazel catkins dance in the wind. These are beautiful, and a symbol of early spring, but each catkin is a mass of male flowers, the structure being so well suited to being flung about in the breeze, hurling out pollen as far as it can go but, even then, most of it lands in a halo around the parent. Just think of a flowering cherry tree when its blossoms fall. They invariably form a pretty pink areola around the trunk, extending out as far as the canopy. The pollen of most plants will form such a ring of varying distance around the parent plant, although some may escape into more turbulent air to be carried up into the air spora. From a forensic perspective, wind-pollinated plants can often be over-represented in the samples we take from the crime scene, while insect-pollinated plants can be under-represented. Their pollen might never reach the air, or never fall much further than the ground immediately underneath the parent plant, so finding its traces on a suspect or victim’s shoes and clothing is much rarer, and can be of considerable significance. Pollen of pine, grass, or hazel all might be over-represented in the air spora while daisy, clover, buttercup, sloe, and rose might be under-represented. Some wind-pollinated plants can be meaningful if their pollen production is moderate – nettle and dock are common, but they are generally more useful forensic markers than grass. Although distributed by wind, in
general, their pollen grains are fewer and less efficiently dispersed. One gradually gets to know the dispersal dynamics of various species.
There are always exceptions – that is just the nature of ecology – and, in one particular case, the presence of grass pollen, generally not useful, was vital. A colleague of mine in New Zealand, Dallas Mildenhall, was working on a murder case where, as it was revealed later, the offender had dumped his victim in a river and the body had floated downstream from the riverside crime scene. The task was to find the place where she had met her end. After her cardigan was peeled off her rotting corpse, grass leaves and pollen were laboriously collected from it. What was strange was that instead of having a single pore like virtually all other grass and cereal pollen, these grass pollen grains had two pores. This is rare indeed. One occasionally finds an aberrant pollen grain, malformed during development, but this aberration was obvious in all of the grass grains on the victim.
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