Who are you: Strategies for Presenting Forensic Anthropology and Human Variation in the Classroom

Transcription

1 Who are you: Strategies for Presenting Forensic Anthropology and Human Variation in the Classroom K. Lindsay Eaves-Johnson, M.A., University of Iowa Nancy Tatarek, Ph.D., Ohio University Philadelphia, PA 2007 American Association of Physical Anthropologists, Education Committee Fossils, Bones and Primates: Enriching High School Teaching

2 Who are you: Strategies for Presenting Forensic Anthropology and Human Variation in the Classroom (Lesson) Subject tie-in with General Science: Criminology, Math, Anatomy, Biology, Sociology, Writing Objective: Students will be able to identify major skeletal elements, determine relative age at death, biological affinity, to sex pelves, and determine stature. A Bone to Pick When people see human skeletons, they usually think of Halloween or something similarly creepy. Bones have had a bad rap for years, but recently, some popular TV programs, such as Bones, CSI: Crime Scene Investigation, or Forensic Files, just to name a few, have started turning public opinion around. Now, there are millions of people (maybe even you) who already know the amazing and exciting things that bones can tell trained researchers. The people who specialize in the study of human skeletons, whether they are prehistoric or recent, are called Physical Anthropologists. An Anthropologist is someone who studies people. A Forensic Anthropologist specializes in the study of recent human skeletons in a medico-legal context. This means that the results of their study may end up in court, or may help to solve a crime. MNI The minimum number of individuals assessment or the MNI, as it is usually referred to, is the first step in any investigation in which human remains have been separated from the body as a whole. This is often the case in skeletal specimens who

3 have not been embalmed, as the soft tissues decay, leaving the associations between the bones loose. These loose joints are easily disarticulated or pulled apart by animals or even by jarring movement. Most forensic cases that involve skeletal remains have been disarticulated (or the joints have been pulled apart) in some fashion. It is the job of a forensic anthropologist to determine the minimum number of individuals that could have contributed to the pile of bones at hand. This is determined by sorting the bones into lefts and rights for symmetrical elements. Two right humeri would tell you that more than one individual is represented, and would lead to an MNI of two. If there is no duplication of elements, the MNI is one. Use The Human Skeleton handout provided to aid you. Age at Death Estimate Age at death is estimated in several different ways. If teeth are present for the individual, it is possible to determine age by which teeth have erupted or come in. The pattern of tooth eruption is relatively predictable and often provides the best estimates of age for individuals younger than 25 years. After this point in time, all of the permanent teeth have erupted and wear on them is variable making estimates less certain. A young person who does not take care of their teeth could be confused, for instance with a much older individual. You may use the handouts entitled Human Dental Arcades and Sequence of Tooth Eruption to aid you in your determination of age. Another way to determine age, which is used when crania or head bones are present, is to examine the closure of the cranial sutures. The braincase or cranium is not really one big round bone, but is rather composed of many oddly shaped bones, that are all bonded together as an adult. Sutures are the squiggly lines seen on the cranium and are

4 the places where two or more bones meet. In very young people, these sutures may be open, so that after death, the skull falls apart like a puzzle. After age 17, however, the bones start to knit together and the sutures close. In some older individuals, these sutures may be completely obliterated (invisible, seamless). Again, like tooth eruption, there are fairly predictable and well documented times when theses sutures close or even obliterate. However, this method is often used to grossly classify individuals as: Neonate (newborn), Infant, Subadult (juvenile) and Adult, not as particular ages. The last method we will consider is similar to the examination of suture closure. This method examines the closure of the epiphyses or ends of bones. Most long bones are made of two parts: the diaphysis (the shaft) and the epiphyses (the knobby ends). These parts are unfused in young people and knit together at predictable points in time. It is because these parts are not stuck together, that your limbs are able to grow. The diaphysis grows up and down towards the epiphyses; when your epiphyses fuse to the diaphysis, you stop growing for good. Below is a partial list of some bones and when they fuse: 1. Hip Joint (Proximal femur)-fuses between years. 2. Ankle (Distal tibia and distal fibula)- each fuse between years. 3. Knee (Distal femur and proximal tibia)- each fuse between years. 4. Wrist (Distal radius and distal ulna)- each fuse between years. 5. Shoulder (Proximal humerus)- fuses between years. Another method, not considered here, is examination of the pubic symphysis.

5 Biological Affinity Anthropologists agree (and genetic evidence supports) that all humans alive today are one species, Homo sapiens. Where anthropologists differ is on their views of race, often called ancestry or biological affinity. Some physical anthropologists do not use racial categories in describing humans, arguing that race has no biological meaning and is more of a social construct. Supporting this view is research that has shown that there is more variation within so-called racial groups than between them. In addition, admixture (inter-racial matings) may lead to persons of indefinite racial characteristics. This is more and more common in many cosmopolitan cities. The race-as-social construct paradigm, however, presents a problem for forensic anthropologists, who are daily faced with the problem of needing to estimate race for law enforcement agencies. For these forensic professionals, the only reason that so-called racial differences are of interest is in order to identify individuals, not to make sweeping judgments about a group of people. In identifying persons for law enforcement, forensic anthropologists apply biological traits to socially meaningful labels (race/ethnicity categories). This is perhaps the most difficult task a forensic anthropologist must perform. Many variables affect the attempt to link biological traits to social labels. As mentioned before, humans vary more between individuals than between groups labeled as races. Movement of people across the planet, inter-mating between groups and changes in how cultures construct racial identity can make the forensic anthropologist s task much more difficult. For instance, an individual may exhibit biological traits associated with individuals of African or African-American ancestry. However, this same individual

6 may self-identify as white or Caucasian. It is typically the self-identification that is recorded on personal records such as a driver s license. Individuals of mixed heritages may choose to self identify with one group versus the other, yet may possess skeletal traits of both. Most of the skeletal traits useful for distinguishing between ancestry origins are limited to the skull. Differences in the shape and size of the eye orbits, nasal shape and size and cheekbone structure are several of the more distinguishable features. Some groups differ in their limb proportion (ratios of limb length to stature, for example) or in the curvature of their femur (upper leg bone). Use the three handouts of Cranial Morphological Features with regards to ancestry to guide you in making a racial estimation. Sex Designation There are many physical differences between the sexes. In general, males are more heavily built or robust than females, who are said to be gracile. These differences manifest in varying degrees depending on the individual. The easiest persons to sex by their bones are those showing the most extreme level of robusticity or gracility. Persons of intermediate body form often fall into a gray area of indeterminate (meaning that the researcher could not figure out their sex with any degree of certainty). Prepubescent individuals cannot be sexed reliably since it is the hormones that come with adolescence that cause these skeletal differences between the sexes. Many of the more visual patterns of sexual dimorphism (literally meaning two bodies, one for males and one for females) are centered in the pelvis and in the cranium.

7 It is important to note, however, that while the bones may look different, both sexes have the full complement of bones (i.e. both sexes have 12 ribs). The pelvis is the best indicator of sex because females are built to reproduce (whether they choose to do so or not), and this capability is reflected in the configuration and shape of their pelvic bones. The cranium also shows patterns of robusticity and gracility that are easy to see with the trained eye. This kind of analysis, using only your eyes, is called anthroposcopic and can be applied to both the cranium and the pelvis. Use the two handouts for Sexually Dimorphic Features to aid you in making a sex determination. Stature Estimation Stature or height is commonly found on many types of records e.g. driver s licenses, and medical records. Forensic anthropologists can determine stature in two ways. The first method, called the Fully method, necessitates a nearly complete skeleton. Measurements are taken from the skull, vertebrae (except cervical vertebra 1), sacrum, femur, tibia, talus and calcaneus. These measurements are totaled and an estimation of the total heights of the vertebral disks is added to obtain stature. The second method in determining stature is more commonly utilized in situations of fragmentary remains (like forensic cases). A single bone (usually the femur or tibia, which provide the best estimate of stature) is measured and plugged into a formula specific to ancestry and sex. This method is usually associated with Trotter and Gleser. Provided are formulae for males and females of different racial backgrounds. Use the formula for the appropriate sex and biological affinity (as determined from your previous analyses) in making your estimation of stature. Femur length is provided on your Lab sheet.

8 Stature formulae for the femur (Male) White: 2.32 (femur length) ± 3.94 African-American: 2.10 (femur length) ± 3.91 Asian: 2.44 (femur length) ± 3.80 Hispanic: 2.44 (femur length) ± 2.99 White: 2.47 (femur length) ± 3.72 Stature formulae for the femur (Female) African-American: 2.28 (femur length) ± 3.41 References: Bass, W Human Osteology: A Laboratory and Field Manual, 4 th edition. Columbia, MO: Missouri Archeological Society, Inc. France, D.L Lab Manual And Workbook for Physical Anthropology, 3 rd edition. Belmont, CA: West Wadsworth Publishing Company. Walker, P. and Wood, E Crime Scene Investigations: Real-Life Science Labs for Grades San Francisco, CA: John Wiley & Sons, Inc. Wolfe, L.D., Lieberman, L.S., and Hutchinson, D.L Physical Anthropology: Laboratory Textbook, 5 th edition. Raleigh, NC: Contemporary Publishing Company of Raleigh, Inc. Skeletal exhibits are courtesy of the UI Teaching Collection