Cut marks, saw marks, and forensic anthropology

Human skeletal remains are not a common occurrence at forensic scenes but, when present, they can preserve a great deal of information about the events surrounding the deposition of a corpse. Forensic anthropology, the field that specializes in the analysis of human skeletal remains in medico-legal contexts, has garnered a good deal of attention from the popular media in recent years. Most of that attention comes from Fox's drama series Bones, which ran from 2005 to 2017 and followed the exploits of forensic anthropologist Temperence Brennan (a character from the novels of forensic anthropologist Kathy Reichs). Suffice it to say, forensic anthropology is now among the most popular courses offered in anthropology departments (including at UNCG where I teach), and undergraduate concentrations and graduate programs in forensic anthropology have popped up across the country. 

Forensic anthropology encompasses a wide variety of methods and techniques, one of which is forensic taphonomy. Taphonomy, broadly defined, is the study of how organic remains (like skeletons) transition from living to static entities. In a forensic context, we ask the question "what happens to a person between death and discovery"? A class of taphonomic data, known as bone surface modifications, or BSMs, is particularly useful for answering this question. Marks on bone surfaces, like carnivore tooth marks, saw marks, insect damage, and the like, can provide critical evidence concerning an individual's death and their body's journey after death. Some insects, for example, are only active on the surface, so if we find damage from that particular insect on human bones, we can be sure that the bones were exposed on the surface, at least for some period of time. A few years ago, in a high-profile murder case in North Carolina, where I live, marks on the bones of a human skeleton were used to help identify the saw used to dismember a body. 

Last fall, my friend and colleague, Travis Pickering, who has spent the better part of 25 years studying taphonomy, was solicited to write a review on the use of BSMs in forensic anthropology for the journal WIREs Forensic Science. He graciously invited me to collaborate on the undertaking, and he and I spent the last year researching how BSMs were integrated into the forensic sciences and how they've been used in crime scene reconstruction. The result of those efforts is an article titled "Cruel traces: bone surface modifications and their relevance to forensic science." (I wish I could take credit for the clever title, but that was all Travis.) As much work as they are, I enjoy writing review articles that cover such a wide swath of a particular field of inquiry because they force me to explore literature that I otherwise might not even have come into contact with. 

Several key themes emerge in our review, namely that: (1) the study of BSMs developed first in the paleontology and archaeology of the mid- to late-1800s and was later adopted by forensic investigators; (2) ultimately, a BSM's utility for forensics (or any other field) is only as good as our ability to link that BSM with a particular process, and that link can only be established through systematic observations of a process actually producing a specific BSM; (3) the features of the BSM itself are not always enough to provide a positive identification, and contextual information must always be used (e.g., serrated knives and shark teeth create very similar striations on bones surfaces, but if the bones were recovered far inland, a shark origin is much less likely); (4) the admissibility of expert scientific testimony in federal courts (the so-called "Daubert" standards) privilege the validity of a scientific methodology over the expertise and experience of any one scientific expert.

As an example, consider a linear striation on the surface of a bone recovered from a crime scene. Now, we might logically interpret that mark to have been produced by a knife. That's all well and good, but lots of things can create a linear mark on a bone: a small, sharp sand grain on the ground, the tooth of a scavenging dog, and so on. How might we know that the knife is, in fact, the source of the mark? Well, for one, we need to conduct an experiment where a knife is observed to create a particular mark on a bone's surface (this can be done with donated human skeletal material or, more commonly, the bones of other mammals like deer or pigs). That way, we know for sure what a knife mark looks like. There are lots of different types of marks, though, and even the same knife can create slightly different marks depending on how it is wielded, so one experiment is typically not enough. However, what if a knife was found alongside the human skeletal material? This sort of contextual information, when considered along with the morphology of the mark itself, can provide additional clues and make our identification that much more probable. When this evidence is presented in court, its admissibility, at least according to federal standards, will have less to do with the experience of the expert witness than with the rigor of the methodology used to identify the BSM. 

Importantly, no methodology can definitively, with 100% confidence, identify the source of a particular BSM. Why not? Well, forensic investigators do not themselves witness a crime: the relevant details must be reconstructed. This is where we get the phrase "crime scene reconstruction" and its common association with archaeology, and for good reason. Forensic investigators are in many ways like archaeologists: whereas archaeologists use artifacts and architecture to reconstruct ancient cultures, forensic investigators use evidence to reconstruct a crime. This means, though, that we must work with probabilities, rather than absolute certainties. When we are able to match up a BSM from a crime scene to an experimentally produced BSM, it becomes highly probable, thought not absolutely certain, that the object that created the crime BSM is the same as the object that created the experimental BSM.

A major hurdle for forensic investigators is that some BSMs can be difficult to tell apart from each other. The marks produced by different types of saws, for instance, share many features. So, too, do the marks produced by different types of knives. With so much overlap, how similar do the little bumps, grooves, and edges of a crime BSM have to be to an experimental BSM to be considered "the same"? What features should we even be looking at, and how do we define them? One analyst's "deep groove" may be another's "V-shaped striation." This sort of inconsistency makes it difficult for BSM analysis to attain Daubert-level methodological rigor. Travis and I conclude with the suggestion that computerized image analysis of BSMs coupled with statistical classification might get us closer to reaching that level of rigor. Either way, it will be interesting to see how the field progresses from here.

Forensic anthropology and political violence in Guatemala

Between 1960 and 1996, Guatemala experienced a brutal civil war that cost the lives of over 200,000 people. While the roots of the conflict stretch back nearly 500 years to the exploitative policies of the Spanish Empire, it was in 1960, in response to a CIA-backed coup that overthrew the country's democratically elected president, that a rebellion broke out to overthrow a repressive military regime. Among the most tragic features of this conflict was the systematic murder of ethnic Mayans, who were seen as rebel sympathizers.

While we were in Spain in the spring of 2019, my wife and I visited the Museo Nacional de Antropología in Madrid. The museum had an exhibition featuring a series of haunting photographs by Jonathan Moller, who documented the work of forensic anthropologists involved in the recovery, excavation, and identification of skeletal remains from the disappeared. This is taken from the exhibit:

Since 2000 a Guatemalan citizens' movement has sought justice and challenged impunity. The exhumations and subsequent investigations by forensics have played a key role in that effort, as they offered survivors the opportunity to expose the truth, providing concrete evidence of the atrocities committed in the war. For many years, the government of Guatemala buried the truth about these killings and massacres, just as they buried hope for a better life in Guatemala. The perpetrators of the crimes have responded to the exhumations by unleashing a new wave of political assassinations and death threats to prevent the truth from coming to light.  

The exhumations bring back the pain and horror, but at the same time they impart healing and closure to the surviving families. The survivors are finally reunited with their loved ones, and they are able to mourn and give them a proper burial in the village cemetery, to be at peace with them and with themselves, since many feel guilt for having survived. The exhumations, mourning and re-burials help the survivors recovery their dignity. 

These photographs were taken between 2000 and 2001, when Jonathan Moller was part of the forensic anthropological team of the Office of Peace and Reconciliation, which worked in the municipality of Santa María Nebaj. They represent a starting point to begin to tell the story of the repression and unspeakable violence suffered by the Mayan peoples of Guatemala, and they can only begin to convey the emotion and intensity of what was experienced at that time. Jonathan witnessed the families' pain and grief as they relived these horrible atrocities, and he also shared their joy and celebration at recovering the remains of their loved ones.

The recovery of historical memory allows us to know the past to understand the present and thus have references to build a just and peaceful society that values above all the life and dignity of people.

 The images are extremely powerful--here is just one that I snapped with the camera on my phone:

A member of the forensic team carefully lifts the remains of two men who
were killed in the violence in the 1980s. Jonathan Moller, Nebaj, 2001.

Just another example of how anthropology matters. You can read more about these efforts at the Fundación de Antropología Forense de Guatemala. 

Osteology in the Carolinas

I attended the first meeting of the Osteology in the Carolinas Interest Group (OCIG) this past Saturday (2/8). The event was organized by Gwen Robbins Schug (Appalachian State) and Dale Hutchinson (UNC-Chapel Hill) and was held at UNC-Chapel Hill. The purpose of the group is to be "a gathering focused on the analysis and interpretation of human skeletal remains from contexts pertinent to bioarchaeology, forensic anthropology, and paleoanthropology." In his introductory remarks (after showing off a hilarious t-shirt ode to syphilis), Dale noted that most researchers with these interests often fall between traditional disciplinary boundaries, so the group was meant to fill that gap.

Thirteen papers were given, and I would say that there were between 20-30 attendees. I was only able to stay for part of the morning session, but those papers that I did see were very interesting. Some snippets from my notes of the meeting:

• Chin-hsin Liu (Appalachian State) presented on the bioarchaeology of Bronze and Iron Age burials from Thailand. It was nice to hear from an area and time period about which I know almost nothing. Chin-hsin did say that many of the skeletons could not be analyzed in detail since they are left exposed by the state for tourism. Isotopic data indicate that populations tended to eat more-or-less the same diets even as they experienced a number of techno-sociological changes from the Bronze to Iron Ages.
• Sara Juengst, a PhD student from UNC-Chapel Hill, spoke about her research in the Titicaca Basin of Bolivia. She discussed how strontium isotope data can be used to identify the geographic area where individuals grew up and lived. Using this data, she found that a couple of the analyzed burials contain "non-local" individuals that were, perhaps, she suggested, pilgrims from other regions.
• Chuck Hilton, our colleague at UNCG, gave a really interesting talk on his research with human remains from Alaska. Essentially, he is interested in tracking skeletal changes associated with the shift from caribou- to whaling-based subsistence economies among Alaskan foraging populations a couple thousand years ago at a site called Point Hope. Chuck noted that data on the skeletal health of forager populations tends to be limited, as they are highly mobile and do not typically produce large cemeteries. Luckily, there are around 400 skeletons from this site, and Chuck found, intriguingly, that the folks practicing whaling were much less healthy than the earlier, caribou-hunting, people. Tuberculosis was especially prevalent in the former population (Chuck suggested that this could be linked either to increased marine mammal consumption or contact with infected NE Asian populations). The question becomes, of course, if whaling had such negative repercussions for health, why practice it? I was wondering if this isn't an example of costly signaling−whaling is, after all, a dangerous and, as Chuck put it, "boom or bust" proposition, so perhaps the individuals that engaged in it gained added prestige (and, thus, mating opportunities). I'll have to get his take on this.
• Megan Perry (East Carolina) talked about her team's work at the very famous site of Petra (you may recognize the picture below from Indiana Jones and the Last Crusade−this is the city's treasury building). Orthodox thinking tells us that as a large, cosmopolitan urban center, Petra would have been ridden with diseases. However, preliminary analyses of the human remains suggests a surprisingly healthy population, and Perry and her team plan on testing this hypothesis further. 

  

  The treasury building at the ancient Nabataean city of Petra (courtesy of UNESCO).

• The last talk that I was able to hear was from Dan Temple (UNC-Wilimington). He was looking at human life history trade-offs with a collection of Jomon skeletal remains. Some background: bodies only have so much energy to delegate to various tasks like growth, maintenance, and reproduction, and life history theory is interested in understanding how the body uses these limited resources. Almost all individuals undergo some sort of stress early in development (low birth weight, disease, etc.), and human physiology is plastic enough to devote extra energy to combat these. The question is how does this impact the rest of an individual's life? Temple tested two models: (1) that these early stressors actually better prepare individuals for other setbacks later on; and (2) that the extra energy used early on in development actually makes those individuals more susceptible to later insults (a "borrow now, pay later" sort of idea). Using linear enamel hypoplasias, which are imperfections in the formation of tooth enamel that reflect episodes of stress, Temple found that those individuals affected by hypoplasia earlier on in their lives had more pathological conditions later on and lower life expectancy. This supports the "borrow now, pay later" hypothesis.

There were a number of other talks that I'm sorry I missed, including our department head, Bob Anemone, who talked about his predictive geospatial modeling, Steve Churchill (Duke), who discussed new hominin discoveries in South Africa, and Mark Teaford (High Point University), who talked about the latest in dental microwear. Looking forward to attending this get-together in the future.

Forensic anthropology in conflict zones

The popular press has taken some recent shots at the utility of anthropology specifically, the social sciences generally and, most broadly, a liberal arts education. While this knowledge may not produce a bunch of millionaires, it does make real differences in the lives of real people. We (the Department of Anthropology at UNCG) hosted a great talk this past Wednesday (November 6th) that demonstrates this very process in action. David Hines, a Ph.D. candidate at the University of Florida, presented on his forensic anthropological work excavating mass graves in Iraq. David originally contacted the department because his father taught at UNCG and, during the few months a year that he is in the states, makes him home in Greensboro. Currently, he serves as a forensic anthropology trainer for the Iraq offices of the International Commission on Missing Persons.

The numbers that Hines cited are staggering: an estimated 300,000 to over 1,000,000 missing people are thought to be buried in known or unknown mass graves within the country, most as a consequence of Saddam Hussein's regime. Hines related that most of these deaths occurred during the Iran-Iraq War (1980-1988), political infighting, the murder of political dissidents, terrorism, and the Anfal campaign (the genocide of the Kurds and other non-Arab populations in the late 1980s). He gave a nice overview of the political situation in the country (which is critical to understanding how this sort of work can be carried out) and how they go about finding and excavating the mass graves.

The talk was really, really well attended (350+ showed up), thanks largely to the organizational talents of our Student Anthropological Society. A huge thanks to David for taking the time to visit!