The long-standing problem of estimating the age and sex of subadult skeletal remains has been significantly "solved" with the advances in understanding the growth and development patterns in the skeletons of young people. Kyra Stull, an anthropologist and forensic researcher at University of Nevada, Reno, and Danielle McLeod-Henning, a physical scientist at NIJ, share more about this research with NIJ writer and host Jim Dawson.
Reading and Resources
- Meeting the Forensic Challenges of Subadult Skeletons
- Subadult Virtual Anthropology Database from the University of Nevada, Reno
- Investigation of subadult dental age-at-death estimation using transition analysis and machine learning methods
- A Radiographic Database for Estimating Biological Parameters in Modern Subadults
SPEAKER 1: Welcome to "Justice Today," the official podcast of the Department of Justice's Office of Justice Programs, where we shine a light on cutting-edge research and practices and offer an in-depth look at what we're doing to meet the biggest public safety challenges of our time. Join us as we explore how funded science and technology help us achieve strong communities.
JIM DAWSON: Hello, I'm Jim Dawson, the science writer for the National Institute of Justice. Today I'm talking with Danielle McLeod-Henning and Kyra Stull about subadult skeletal remains. Kyra holds a Ph.D. in Biological Anthropology and is an anthropologist and forensic researcher at the University of Nevada, Reno. Danielle is a physical scientist and program manager with NIJ. I want to thank both of you for being here, and first, let me ask Kyra how one would define subadult. When you say that to people, they often look confused, so, if you could define it up front, I would appreciate it.
KYRA STULL: Yeah, thank you, Jim, for that introduction. I'm excited to be here, and I'm happy to try to provide a foundation for the rest of the conversation. So, in biological anthropology, subadult generally is referring to anybody that is an immature individual, which, of course, comes with its own complications. We roughly think about that as someone being between ages of birth and 18 to 20 years of age. Of course, when you then bring in legal thresholds and what that means in a socio-cultural context, that is--kind of changes as you are in different locations. But generally, we're talking about anyone less than 20 or 18 years of age.
JIM DAWSON: OK. And I don't mean to be overly grim, but what this really is, is when you find remains of children for forensic purposes, right, and you're looking at skeletal remains of a 4-year-old or a 9-year-old or a 14-, 15-year-old, how do you tell the age at death. And I guess you work from there. And I think a lot of us in the world have grown up with, well, you can tell the difference between boys and girls because of their pelvis and haven't given it much more thought of than that. But so let me get to that in a minute.
But first I want to give an idea of how big the problem is. When I was looking at statistics on this, there are something like 460,000 children reported missing in the U.S. every year. And most of them come back quickly and are found, and it isn't a big deal, but about one in 10,000 of the kids that go missing are found not alive, I think is the right term for it. So that's the focus of this is that. And NIJ--clearly Danielle looked at this a number of years ago and started focusing on grants. And I wanted to get a feeling from her on why this is important for NIJ.
DANIELLE McLEOD-HENNING: Thank you, Jim. So, as you both know, so NIJ is the research, development, and evaluation agency of the U.S. Department of Justice and is one of the lead funders of forensic science research, encompassing all forensic research disciplines. But of those, we also, of course, include forensic anthropology, where research funds--or where NIJ funds research to improve technologies, techniques, and the application of forensic anthropology to assess biological profile, identify injuries, and estimate time since death to assist in identification and investigation. So, research into subadult biological profile estimation is an identified need of the forensic science community, and it also aligns with NIJ's recently published Forensic Science Strategic Research Plan, which is available now on nij.gov. These NIJ investments are paramount to assisting in the identification of unidentified subadult remains and aiding in death investigation. Not only is this research a need of the forensic science community, it's also a need of the public to bring justice in cases of violent death and to bring a sense of closure to loved ones.
JIM DAWSON: Thanks. Well, that's terrific. And that's--all right. And let me go to Kyra and get to the crux of this. When you're confronted with subadult remains, how are they different from adult remains? You know, we always see: body was found, and it was 35 years old, give or take 5 years, or something like that. And I assume there's standards for that. What are the unique problems with subadults that you face? Or that researchers and forensic people face when they're looking at this?
KYRA STULL: Yeah. So when we generally--when we interact with law enforcement, we generally as—we, as in forensic anthropologists, are usually asked to estimate a biological profile, which is that snapshot of an individual. So age estimation, sex estimation, population affinity, stature. And all of that is used to usually facilitate positive identification. But when we are faced with subadult remains, those individuals are still growing, right? So we haven't actually attained those adult phenotypes that we are all so—you know, we know so well. And even though with soft tissue, you can talk about how tall a child is or what that child looks like, we really don't have enough skeletal collections to have created those biological profile techniques for children. So there are a lot of biological and methodological complexities that come into actually making those estimations. But the real problem has been that we haven't had the data available to make those methods.
So we, as forensic anthropologists, heavily rely on skeletal collections that are usually coming from donors or cadavers, right? So University of Tennessee, Knoxville has the Bass Collection, which is probably the most famous one that started back, you know, over 30 years ago now. But those are primarily individuals that have donated themselves to science or next of kin who donate themselves. And generally speaking, we don't have individuals that donate their children to science if they have died, which is absolutely understandable. But because of that, anthropologists have really been limited in method development to be able to build age estimation techniques or sex estimation techniques. So there's a lot of biological and methodological things that happen, but the first problem was that we actually didn't have data available to make the methods or test the methods or validate the methods. And historically, up until, you know, 5 years ago, we heavily depended on historic skeletons, which are individuals that have died, you know, 150 years ago, which we know have different growth patterns, have different environments, have different--come from a variety of situations that contemporary individuals aren't faced with today. So, using those historic skeletons are not generally recommended for use in a modern context.
JIM DAWSON: So, and as a result of this, you started--the--what--it's called the Subadult Virtual Anthropology Database, is one of the issues you've developed. Could you look at that? And I know this involves, just for people with a, you know, from, you know, not much education on this, you're looking--talking about bones, teeth, structure, growth plates, those kind of things in skeletons, all of those. And I know at different times, from your work and reading your papers, they come into play at different times. So what you look at for a 2-year-old is different than a 6-year-old. It's not just you look at growth plates and you look at the--I mean, these things evolve, and you have to figure that out. But how does that tie in? And you need--as you were talking with all good forensic science, it needs a database behind it. And so, talk about your database a little bit if you would, please.
KYRA STULL: Yeah, absolutely. So, even though back in 2015 when NIJ so kindly awarded me the first grant, we really had major outcomes of that grant to be creating new methods. And while we had planned to create a sample, that is really when we first came into realization that we can't do anything in terms of method development without sample-building first. And so at that time, that first grant went into working closely with the individuals at the Office of the Medical Investigator in New Mexico. So they now also were funded, I think a year later, to develop the New Mexico Decedent Image. They also were working towards the same problem. Anyway, so we worked with them first on an American sample. So, between them and the Office of the Chief Medical Investigator in Baltimore, Maryland, we collected about thir--data from about 1,300 individuals in the United States. Since then, we have worked with collaborators in seven more countries. So that is Colombia, Brazil, France, the Netherlands, Angola, South Africa, and Taiwan. And that was funded from the NIJ as well in 2017. So now we have data collected on these age indicators, and more now, from approximately 5,000 individuals, which is pretty remarkable. So that is, by far, the largest repository of skeletal and dental reference data that is available.
And so, in these first two projects, we focused heavily on diaphyseal dimensions, epiphyseal fusion, dental development, and vertebral neural canal dimensions. And those first three variables are really the classic age indicators that we think about, and really they all have to do with how tall an individual is and how you go from having deciduous dentition to permanent dentition. And that is really the Holy Grail of all subadult age estimation techniques that have ever existed are from those three indicators. So since then, we also, like I said, have data from the vertebral neural canal, which gives us an idea of potentially a nonspecific stress indicator. And we now also have a grant from the NIJ from 2019, where we are collecting craniometrics, dental metrics, dental morphology, and cranial morphology from the United States sample. So the database is growing not only in individuals that comprise it, but also of the data within it. So I think at this point we have over--in some individuals, have over 450 data points collected on them, which is pretty remarkable.
JIM DAWSON: OK. It is. And let's explain to me then if you're looking--and let me--I can be a little simplistic here, but…
KYRA STULL: No, let's talk about it.
JIM DAWSON: Yeah, if you have three sets of remains and they're all subadults, what--how do you distinguish--I mean, I know they're different things at different stages, mentioned that, but what is it you're looking with when you're presented with this, if you walk up and there are the remains on the table? Do you start with size? How do you go about this? What do you look at? What do you look for?
KYRA STULL: Yeah, I think that that's a great question. In terms of those age indicators that we think of, they all kind of tell us different...or I should say they essentially put us in the correct location and ontogeny, and by ontogeny, I just mean growth and development, so how old that individual may be at certain times. So when we are very young, we can heavily rely on something like diaphyseal dimensions because they have a very strong correlation with chronological age. So, you know, if you think about how quickly kids grow when they're very young, that is how we can depend on those diaphyseal dimensions, because it's the length of their arms and their legs. But as you continue to increase in size and you grow older, the part of our body that's allowing us to grow is also that epiphyseal fusion. And so epiphyseal fusion actually occurs when you stop growing, right. So, we get through that wonderfully uncomfortable period in life of puberty, and then you've reached your maximum height. And during that really wonderful, uncomfortable time is when we can look at those fusion patterns, right?
So where diaphyseal dimensions are really useful for young individuals, epiphyseal fusion is really helpful in individuals like from, you know, 10 years of age to 20 years of age. So you kind of have this trade-off between those two. And then dental development is really lovely because it occurs through at least the first two thirds of growth and development, right? So when you are a kid, you actually already have--well, I should say when you're in your first year of life, you already have your first molar growing inside of your jaws. And that first molar, so we would be able to look at that, you know, from the time it erupts at six and then through its root development three years later. And we all know what kids look like, you know, losing their teeth and getting their permanent teeth in. And that is--that mixed dentition and growth and development of their teeth, we can kind of use. Mostly, it's going to be the most informative from that 5- to 12-year-old period. So all of these indicators kind of tell us a different story about the individual, but then also, importantly, how they're interacting is going to give us the best idea.
So I think, Jim, you and I talked about it for the previous publication, but because these are all telling us different stories, there's no really best age indicator that anthropologists can walk away from and say teeth are always going to be it or long bones are only going to be at or epiphyseal fusion is going to be perfect, because really it all depends on how old that individual is for which indicator is going to give you the best information, and also the interaction of the traits that you have available, right, because we generally are not faced with remains that are complete skeletons also. So we have to be able to work with what we have available.
JIM DAWSON: Thanks for listening to part one of this episode. Please stay tuned for part two of this conversation about subadult skeletal remains.
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Opinions or points of view expressed in these recordings represent those of the speakers and do not necessarily represent the official position or policies of the U.S. Department of Justice. Any commercial products and manufacturers discussed in these recordings are presented for informational purposes only and do not constitute product approval or endorsement by the U.S. Department of Justice.