by Sue Black
One day we might not even need to carry passports as our entire identity could be implanted in our hands, or indeed any part of our body. Such technology might sound the death knell for some aspects of the forensic anthropologist’s work. But not in my lifetime.
10
The Foot
“It’s a fact the whole world knows, that Pobbles are happier without their toes”
Edward Lear
Poet, 1812–88
I have always hated feet, living or dead. I hated dissecting them and I hated having to try to identify all those misshapen little nodular excresences that make up our bony toes. Feet have bunions, corns, callouses, warts, verrucas, gout. They can produce up to half a pint of sweat a day and they even make their own cheese. I hate it when you have to perform a postmortem on a decomposed body and you know that when you turn a sock inside out you are going to have to sift through the gloop of yellow-brown, slimy mush to find the lumps of bone. You might well find the floating toenails in this foot soup, and that sends a shiver down your spine. Gnarled, misshapen, fungus-ridden, thick slabs that have the cheek to ingrow: I hate them most of all.
In truth, feet are often overlooked during forensic postmortem examinations, which is ironic when you consider that they play such a big part in the iconography of the fictitious CSI forensic world, poking out cheekily from under a white sheet, usually sporting a fetching toe tag. It is also a mistake, because they do keep a lot of information hidden away under their arches. And that draws a glimmer of grudging respect from me.
To appreciate the foot we need to understand its purpose. The modern foot has two principal functions: to support the weight of our body when we are standing upright and to act as a mechanism of propulsion when we want to move. Pretty much nothing else.
The early twentieth-century naturalist and anatomist Frederic Wood Jones waxed lyrical about the foot: “Man’s foot is all his own. It is unlike any other foot. It is the most distinctly human part of his anatomical make-up. It is a human specialization and whether he be proud of it or not, it is his hallmark and as long as Man has been Man and so long as he remains Man, it is by his feet that he will be known from all other members of the animal kingdom.”
He was right: there is no other foot in the animal kingdom that looks like ours, and that is why palaeontologists get so excited when prehistoric human foot bones are found. A fossilized example from the Hadar region of Ethiopia showed that by about 3.2 million years ago our human ancestors were bipedal and walking on a modern-looking foot, a discovery that is supported by a number of other finds, the most important being the foot bone of a member of the Australopithecus genus of hominin from which we are believed to be descended: Australopithecus afarnesis AL 333-160. This specimen is a left fourth metatarsal and it is arched—a feature that is unique to the modern human.
In the human embryo, the lower limb starts to form around 28 days after fertilization, a couple of days after the upper limb has begun to develop. By day 37, a footplate resembling a paddle appears at the end of the limb and within four more days, digits are visible. Bones will begin to form towards the end of the second month. At birth, nineteen of the bones in the front and middle parts of the foot will be formed, plus the calcaneus, our heel bone, and the talus, which sits on top of it to make our ankle. Once growth is completed, each adult foot will have around twenty-six bones in total.
The calcaneus is the first foot bone to be visible on an X-ray, between the fifth and sixth month of our gestation, and the talus can be seen by the sixth or seventh month. The cuboid, the most lateral of the tarsal bones, may show bone formation just before we are born or within the first couple of months afterwards. In the past, looking at the developmental stage of these three bones was the most straightforward way of assessing the age of a fetus, and it was used by early pathologists to establish whether a deceased baby who had been delivered prematurely or aborted would have survived without medical assistance. Nowadays, of course, babies are viable from a much earlier age, but this information was often relied upon in the past to decide whether legal action should be taken against a mother.
Like our feet, our footprints are unquestionably human and there is no other animal that makes a similar print. Some or all of the heel, the lateral (outer) border of the foot, the ball and the pads of the toes may be visible in the impressions or marks we leave behind when our bare feet come into contact with a substrate, depending on the nature of the surface or material on which we have trodden. The medial (inner) edge will not leave a print as the internal structure of the foot raises this region into a series of arches that give our feet their elasticity and stability—the hallmark of the human foot.
Because a baby’s foot leaves a fuller print, there is a popular belief that the arches do not develop until about two years of age. In fact they start to form quite early: it is the presence of a pad of soft tissue that gives a young child’s foot its flatter appearance.
Ancient footprints preserved through time have helped to confirm the earliest dates established by archaeologists and palaeontologists for habitual human two-legged propulsion. It was another trio of Australopithecines who left behind some of the most remarkable evidence of their stroll across our planet’s surface millions of years ago. The Laetoli footprints in Tanzania, a trail of about seventy impressions made in volcanic ash, were covered over by a further volcanic eruption and remained hidden for 3.6 million years until they were found by the celebrated British palaeoanthropologist Mary Leakey in 1976.
The Australopithecines walked in a modern heel-strike, toe-off mode, with a short stride that suggests a more diminutive stature than that of the modern human, a presumption confirmed by other bones. The Australopithecine footprints were undeniably “human” and they provided us with the earliest date we have for the emergence of competent bipedality as a preferred mode of locomotion. What these impressions also finally resolved was the argument about which came first: big brains or bipedal locomotion. Studied alongside research on the skulls and limbs of Australopithecines, they confirmed that it was, indisputably, walking on two legs, and the freedom it gave us to use our upper limbs to explore, that first characterized us as human. Perhaps only then did we start to work on our big brains. Standing upright was the pivotal action that changed the future of our species, other species and our planet. As Wood Jones had insisted, we owe it all to the humble foot.
Other countries might not be able to match the richness of the palaeontological treasures of Africa, but one of the oldest sets of hominid footprints found so far outside that continent was discovered in the UK. The Happisburgh footprints, made by a group of adults and children, were revealed in 2013 in Norfolk, in the muds of an ancient estuary, and dated to between 850,000 and 950,000 years ago. They were stumbled upon by a team of scientists who were working on another project after the protective layer of sand that had been concealing them was washed away in the huge St Jude’s storm of that autumn. The sediment lay below the high-tide mark and the scientists knew they were in a race against time and tide to record them before the sea eroded them permanently. Their swift thinking won them a Rescue Dig of the Year Award after their pictures were exhibited later at the Natural History Museum. Within two weeks of re-emerging, the footprints had gone.
Footprints, and what we can tell from them, fascinate scientists across many different specialisms. While clinicians will look at them to see if there is an abnormality they may be able to fix, forensic podiatrists study them to compile evidence for the court. Perhaps a footprint has been left in blood at a crime scene, or in soil outside a window, and it may be possible to match this to a suspect. Obviously, this investigative approach has greater value in situations where people habitually walk around in bare feet. In cooler climates, and outside the home, it is much more likely that we will find shoe prints.
But these can be useful, too. Shoes can be matched to the person they belong to, especially when they have been worn without socks or tights. If you look inside one
of your shoes, you will see some kind of replication of your footprint. A podiatrist could compare this print, or at least a version of it, with your foot to determine the likelihood that the shoe and the print are yours.
Footprints can give us quite a lot of information about the person, or people, who left them. For example, we can estimate the length of their stride and therefore their height, just as it was possible to do with the Australopithecine impressions. We can work out what shoe size they take. We can tell how many people were present at a scene and whether they were standing, walking or running.
If the print of a bare foot is sufficiently clear, we may be able to lift toe prints in the same way as we do fingerprints. These were of some help in identifying the bodies of children after the Asian tsunami of 2004. Toe prints could be compared with bare footprints found around the family home where, say, the child might have climbed on furniture. More recently, Japan has been considering setting up a footprint register alongside their fingerprint database. This may sound a strange idea, but there is a logic to it. Because feet are frequently protected by shoes, they tend to survive better in mass fatality situations than other parts of the body. For this reason, the records of some military air personnel may include bare footprints as a potential additional means of identification in the event of a plane crash.
In recent years, probably the most infamous case involving footprint evidence was the murder of Meredith Kercher in Perugia, Italy in 2007. The body of twenty-one-year-old Meredith, a British exchange student, was found on the floor of her bedroom in the flat she shared with three fellow students. One of her flatmates, Amanda Knox, and her boyfriend, Raffaele Sollecito, were charged with Meredith’s murder and a third person, Rudy Guede, a regular visitor to a neighbouring flat, was also later arrested in connection with the crime.
With three defendants, it was always going to be difficult to separate truth from speculation, and at the centre of much of the confusion was some less than reliable forensic evidence, including a partial footprint in blood on a bath mat at the scene. The blood was confirmed by DNA analysis to be Meredith’s; the owner of the footprint was not so easy to determine.
The prosecution alleged that the print was a “near perfect” match with Sollecito’s right foot, but not for Knox or Guede. However, expert witnesses called by the defence pointed out fundamental errors in the testimony of the prosecution’s expert and offered evidence that the print was more likely to be Guede’s. The prosecution’s witness was a physicist, not an anatomist, and it is always troubling when scientific evidence relating to anatomical features is being interpreted by a professional whose expertise is in another discipline.
The custody footprint taken for comparison with the print from the scene was static and had been recorded in ink on paper—two very different materials from the blood and thick fabric involved in the formation of the original print. No attempt had been made to replicate the effects of the much greater absorbency of the bath mat or the consistency of the blood.
Guede opted for a fast-track trial and was found guilty of the sexual assault and murder of Meredith. He was sentenced to thirty years in prison, later reduced to sixteen. Knox and Sollecito were convicted of murder and both served almost four years in jail before being acquitted on appeal. The appeals were then quashed and both were found guilty a second time, only for these convictions to be annulled once more, by the Court of Cassation, the highest court in the land, on the grounds of reasonable doubt. This decision definitively ended the case and Knox and Sollecito walked free.
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The pattern of footprints can tell us whether the person who left them was standing still or moving. We can all recognize people by the way they walk, although we are usually processing other clues simultaneously. Despite my poor eyesight, I can pick out my husband from a distance by how he stands and walks, but I am also going by his size, shape and the clothes he is wearing and, more often than not, because he is roughly where I expect him to be, even if the figure I am looking at is all a bit of a blur.
Gait analysis, the study of the manner in which we move, is quite distinct from this kind of everyday recognition. Experts in this forensic technique claim to be able to match the pattern of movement of an offender—often with nothing more to go on than some very poor-quality CCTV images taken from an odd angle—with that of a suspect in front of them in a police station custody suite. Both offender and suspect, if indeed they are two separate people, will usually be unknown to the expert and probably wearing different clothes, so the rationale is that comparison is being made on gait pattern alone. But the fact that these are very different environments could have a bearing on the way a suspect moves. In the first, they are unaware they are being watched; in the second, they know that their walk is being scrutinized.
It is said that our walk is unique to each of us, but there is no solid evidence to support this theory. Of course, if someone has a particularly unusual gait, such analysis is likely to be more reliable, but the way we move is not necessarily always going to be the same. We walk differently if we are in high heels from how we walk in flats; if we are wearing comfortable or uncomfortable shoes; if we are carrying a heavy bag on one shoulder, or a bag in each hand, or if we are walking uphill on cobbles rather than downhill on an even pavement. We do not yet have enough valid information on how our locomotion may be affected by these and other conditions.
Gait analysis has been presented in court to convict defendants but as the methodology is relatively new, care must be taken over the safety of the evidence. The Rt Hon Sir Brian Leveson summed up the need for caution when he described forensic gait analysis as “a much younger and less scientifically robust area.” A “judicial primer” has now been given to all judges in the UK to clarify for them where the science for gait analysis is reasonably tried and tested and where there is much research still to be done.
In 2013, expert evidence presented by a forensic podiatrist was used by the defence as the basis of an appeal against a murder conviction. Following an altercation outside a McDonald’s restaurant in Wythenshawe in 2006, a twenty-five-year-old man had been shot dead. The case against the alleged gunman had collapsed and he had been acquitted. But if you are party to a murder, you do not have to be the one who pulled the trigger to be charged with the crime, and Elroy Otway, the man accused of being the driver of the getaway car in which the gunman had been a passenger, was tried in 2009 on the basis of “joint enterprise,” found guilty and sentenced to a minimum of twenty-seven years in prison.
The car had been identified and CCTV footage from a service station showed a man filling it with petrol shortly before the murder. The forensic podiatrist called to give expert evidence had compared Mr Otway’s gait in the custody suite with that of the individual on the CCTV recording.
At appeal, the defence counsel argued that gait analysis was not sufficiently advanced as a methodology to be permitted as evidence and they did not accept that the podiatrist was a competent forensic expert. The evidence was, they claimed, circumstantial. However, the three judges hearing the appeal in London considered the evidence as a whole and overruled the grounds for the appeal. The trial judge had, they said, been entitled to rule the evidence as admissible, and to allow the court to hear the podiatrist’s opinion, leaving the validity of the forensic gait analysis open to debate. They did add, though, that they did not endorse the use of podiatric evidence in general. It is important that scientists and the judiciary work together to ensure that what gets into court to be heard by the jury is founded in verifiable science, which meets the required standards of repeatability, reliability and accuracy, and that it is probative.
Running produces a different characteristic human gait and footprint from walking or standing. Standing requires two feet to be in contact with the ground. When we walk, one foot at a time leaves the ground. At the peak of a fast run, there is a phase when there is no contact with the ground at all and the runner is technically airborne. The distinction b
etween walking and running is central to the rules of speedwalking, in which running is prohibited. Hence the rather odd gait synonymous with the sport, which enables the competitors to walk extremely fast while always keeping one foot on the ground.
Human walking has a double-pendulum action called the gait cycle, which involves both a standing and a swing phase in each leg at different times. The stance phase occupies about 60 per cent of the cycle and the swing phase the remaining 40 per cent. Gait involves a combination of movements in a chain across both phases. At any one point in time, a limb is in one of the following positions: heel strike, foot flat, mid-stance, heel off, toe off and swing. Try it. Walk in slow motion and note where each limb is during the different phases of the cycle.
The stance phase begins with heel strike and the swing phase with the toe off. The whole of the foot becomes engaged in the walking motion, from the heel at the back to the big toe at the front. This is why, in a walking footprint, the deepest impressions are made by the heel when it strikes and the big toe when it pushes off. In a purely standing footprint there is no “dig-in” associated with the heel or the big toe.
Although our feet have only two main functions, keeping us standing and moving us around, we can train them to become incredibly dextrous when necessary. Indeed, Luther Holden, a nineteenth-century anatomist surgeon from Birmingham, described the foot as “pes altera manus,” loosely translated as “the other hand.” The bones are homologues of those in the hands, with the seven tarsals in each foot equating to the eight carpals in our hands and the five metatarsals to the five metacarpals. And the phalanges, of which we have fourteen in each hand and each foot, have the same name and position in the toes as they do in the fingers: distal, middle and proximal. Other than our big toe, the hallux, and our little toe, digiti minimi, we simply number our toes from one (big) to five (small) without bothering to give them names.