Attribution of Ancestry

Attribution of Ancestry Screencast 1 Biological Profile Provide information for a positive identification: Ancestry (race or ethnicity) Sex Age Stature - Knowledge of each helps reduce search parameters when attempting to match remains with a missing person’s report ➢ Ancestry - Social Race (or Race) = what we look like - Ethnicity = related to our cultural background (religion, dress, practices, language, how raised) - Ancestry = individual’s ancestral geographic region of origin o Predominantly Asian, African or European - Current debate as to whether the terms race or ethnicity should be used - Ethnic cleansing in genocides o By determining race in genocide cases you are legitimising that people are different, which is why they were killed o Head shape can’t tell you religion or beliefs - Forensic anthropologists commonly adhere to the terminology used by law enforcement in their reports: o White = persons of mainly European descent o Black = persons of African descent o Asian = persons who ancestors originates in the Orient - USA – also use the terms Native American, Hispanic ➢ Census Data - Overlapping of traits that characterise individual groups - Much ambiguity when attributing ancestral group = hard to assign - Majority of characteristics used to assess ancestry apply only to adults - Positive assortative mating o Mating between individuals of similar groups o Similar cultural, social and religious backgrounds o Maintains an identifiable degree of consistency between an individual’s race and skeletal biology - People do not always mate with individuals of the same ancestry = Admixing o May identify with one group socially o Skeleton will show a mix of physical traits ➢ Ancestry - Estimating ancestry from skeletal remains is possible due to geographicallypatterned human variation - Different populations show variation in skeletal shape due to evolutionary processes such as: o Natural selection o Genetic drift o Mutation o Gene flow - Other aspects of biological profile influenced by ancestry o Sexual dimorphism, limb proportions and growth rate ➢ Anthroscopic Traits - Visual identification of traits that differ among ancestral groups - How traits are expressed is divided into discrete categories and not measured on a continuous scale o Subjective → influenced by or based on an individual’s personal beliefs, feelings and opinions - Example: Projection of the nasal bridge o African and Asian populations = non-projecting bridges o European populations = nasal bridge juts forwards a considerable degree o But what constitutes “projecting” and “non-projecting” ➢ Cranial Skeleton - Majority of traits used to determine ancestry found in the cranial skeleton - Focus in on three main ancestral groups – White, Asian, Black - Anthropologists examine four areas: nose, face, vault, jaws and teeth ➢ The Nose - Five features that vary amongst ancestral groups: 1. Root 2. Bridge 3. Spine 4. Lower border 5. Opening - Distance 1 = Nasal root (where the nasals meet the frontal bone) o How far the root of the nose projects in front of the lower border of the eye o White = projects forwards from the face (high) o Black/Asian = narrower and closer to the face (low) - Arrow 2 = Nasal spine (projection bone extending from the nasal floor) o White = spine very pronounced (large and projects forwards) o Asian = fairly small o Black = almost non-existent - Nasal root width (RW) o White = narrow o Asian = intermediate o Black = wide - Nasal opening o White = narrow, shaped like an isosceles triangle o Asian = intermediate o Black = wide, shaped like an equilateral triangle - Lower border of the nose o White = lower border forms a sill or a wall o Asian = still present but less sharp o Black = indistinct and gutter-effect on either side of the midline ➢ The Face - Facial projection (line 3) = caused by differences in jaw size o White = vertical face (possibly receding) due to smaller jaw o Asian = intermediate o Black = face projects forwards because the jaws are larger than Asian or White individuals - Shape of eye orbits o White = angular o Asian = round o Black = rectangular - Projection of the lower border of the eye o Asian population = projects forward of the upper border when viewed from the side o Black/White populations = no projection Screencast 2 ➢ Vault (“brain case”) ➢ Sutures - Wormian Bones o Accessory bones located in the lambdoid suture o Common in individuals of Asian descent ➢ Postbregma - The shape of the area behind the bregma (where the sagittal and coronal sutures meet) o Black = area concave o White/Asian = area flat or slightly convex ➢ Jaws and Teeth - Size of the jaws and teeth differ between ancestral groups o White = teeth too large for their jaws (crowding) o Asian/Black = large teeth but larger jaws (less crowding) - Observe differences in dental arches of upper jaw - Upper Incisors (front four teeth) o Asian = shovel-shaped incisors ▪ Raised edges on the lingual side of the teeth ▪ Particularly common on the upper central incisors o Black/White = spatulate (flat lingual surfaces) Structure White Black Asian Root High, Narrow Low, Rounded Low, Ridged Bridge High Low Low Spine Pronounced Small Small Lower Border Sharp (sill) Guttered Flat, Sharp Width Narrow Wide Medium Profile Straight Projecting Intermediate Shape Narrow Narrow Wide Eye Orbits Angular Rectangular Rounded Lower Eye Border Receding Receding Projecting Brow Ridges Heavy Small Small Muscle Marks Rugged Smooth Smooth Vault Sutures Simple Simple Complex Postbregma Straight Depressed Straight Jaws Small Large Large Palatal Shape Parabolic Hyperbolic Elliptical Upper Incisors Spatulate Spatulate Shovelled NOSE FACE VAULT JAWS and TEETH ➢ Metric Methods - Metric methods provide a single, most probable group for a skeleton of unknown ancestry - Individuals of known ancestry have certain skeletal features measured - Distribution of these measurements is calculated for various ancestral groups - Cranial measurements can be used to attribute ancestry o Popularised by Eugene Giles and Orville Elliot (1962) ▪ A statistical procedure that uses any number of measurements to distinguish between two or more groups o Used the Terry collection and nine measurements to distinguish between White and Black populations (plus Native Americans from the prehistoric site of Indian Knoll) - Example: measuring the width of the nasal opening in two groups of skeletons – one White and one Black o Comparing the measurements from the two groups will show that the White population has a narrower nasal opening (as evidence by smaller measurements) - Deceptive – appear more accurate than they actually are ➢ Problems with Metric Methods - Samples used to generate these methods are not representative of a modern population - Majority research based on Hamann-Todd and Terry collections o Accumulated in midwestern USA during early and middle 1900s o Skeletal changes have been documented over last 50 years - Measurements can be ambiguous – hard to take/replicate - Metric methods quantify what is already observable o If you can’t determine ancestry using morphometric methods, will metric methods be any better? ➢ FORDISC - FORDISC = computer program which determines ancestry through discriminant function analysis of cranial measurements (Jantz and Ousley, 2005) o Looks at within group variation – how much individuals in a group vary o Followed by between group variation – difference between groups (influenced by geography, ancestry, mating patterns) - Data originates from the Forensic Data Bank (1986) - Modern population with institutions such as University of Tennessee contributing the data - 3400 cases to date - Computer assesses how much populations differ from one another and then determines which group an individual belongs to → posterior probability - Posterior Probability o The probability that a hypothesis is true o Higher the number = more likely your individuals falls into that group o Aim for posterior probability approaching 1.0 (greater the number, more confident we are of the outcome) o Posterior probability <0.5 = poor probability - Takes a series of measurements using a number of landmarks on the skull o Measurement 1 = maximal cranial length o Measurement 2 = Nasio-occipital length o Measurement 3 = Maximum cranial breadth Insert your measurements (mm) and select which population you want to compare your skull with - The posterior probability is what we are interested in. It tells us which population our skull most closely matches - The greater the posterior probability, the more confident we are it came from that population - Based on the measurements provided, FORDISC indicates this skull is a black female ➢ Limitations to FORDISC - Will only return correct ancestry attribution when the cranium is complete - Individual needs to belong to one of the populations represented in the program’s reference sample (not everyone is included) - Classifies <1% with confidence (Elliot and Collard, 2009) - Designers argue issues are with how the program is used or misinterpretation of the results - Use with CAUTION