Comprehensive Study Notes on Forensic Anthropology

Introduction to Forensic Anthropology

• Definition of a Forensic Anthropologist:

  • An expert specialized in the analysis of human remains.

  • The role involves the application of anthropology (the study of humans) to criminal investigations.

• Determinations Made Through Bone Analysis:

  • Species: Identification of whether remains are human or animal.

  • Sex identification.

  • Estimated Height ($\sim \text{Height}$).

  • Estimated Age ($\sim \text{Age}$).

  • Ancestry.

  • Cause/Manner of death: Evaluation of trauma, disease, etc.

  • General state of health.

  • Type of occupation or repetitive physical activities.

Bone Basics and Biological Composition

• What is Bone?

  • Bone is a rigid, connective tissue that forms the skeleton of vertebrates.

  • Quantity in the Human Body:

    • Adults: Approximately $206$ bones.

    • Birth: Infants are born with approximately $270$ bones; this number decreases as bones fuse during growth.

  • Biological Status: Bone is considered a living tissue and serves as an excellent source for DNA.

• Functions of Bones:

  • Support and Movement: Provided by the limbs.

  • Protection: Provided by specialized structures such as the skull bones and ribs.

  • Mineral Storage: Acts as a reservoir for essential minerals.

  • Blood Cell Development: Occurs within the marrow.

• Chemical and Structural Composition:

  • $35\%$: Composition of collagen, ground substance, and cells.

  • $65\%$: Composition of calcium (specifically hydroxyapatite).

• Bone Cell Types:

  1. Osteoblasts: Their function is to make and deposit bone tissue (Etymology: "Blast" = Build).

  2. Osteoclasts: Their function is to degrade and resorb bone tissue (Etymology: "Clast" = Chew).

  3. Osteocytes: Known as "watcher cells," they monitor the status of the bone (Etymology: "Cyte" = Sight).

Determining Species: Human vs. Animal

• Comparative Anatomy:

  • Cells: Humans possess round cell structures; animals possess rectangular or linear cell structures.

  • Ribs:

    • Humans: C-shaped; typically numbering less than $12$ (< 12).

    • Animals: Linear/straight; typically numbering more than $13$ (> 13).

  • Limbs:

    • Humans: Children have unfused growth plates.

    • Animals: Process fused growth plates.

  • Muscle Attachment Areas:

    • Humans: Fewer attachment areas; bones are generally straight.

    • Animals: More muscle attachment areas; bones are often curved.

  • Upper Limbs:

    • Humans: Feature a large trochanter and an angular upper head.

    • Animals: Feature a small trochanter and a flat upper head.

Quantitative Identification: Height and Ancestry

• Height Determination:

  • Primary bones used for estimation include the humerus and the femur.

  • Estimations are based on a mathematical relationship between bone length and overall stature.

  • Variables: Formulas for estimation are specific to the individual’s sex, ancestry, and the specific bone being measured. Knowledge of ancestry and sex results in a significantly better height estimate.

• Ancestry Categories:

  1. African Descent: Includes individuals from Africa, the Caribbean, and African-Americans.

  2. Asian Descent: Includes individuals from China, Japan, the Inuit (Arctic regions), and Native American populations.

  3. European Descent: Includes individuals from Europe, East India, Pakistan, and Arab nations.

• Skull Analysis for Ancestry:

  • The skull displays the highest number of distinguishing traits among ancestral lineages.

  • Caveat: This analysis is controversial and may not be highly reliable due to ancestral intermixing; it provides suggestions rather than definitive conclusions.

• Ancestral Traits in the Skull:

  • African Lineage:

    • Orbits (Eyes): Rectangular shape.

    • Nasal Cavity: Wide space between eyes; nasal guttering (no ridges) at the base; wide, rounded nasal opening.

    • Prognathism: Bones stick out (protruding jaw).

  • Asian Lineage:

    • Orbits (Eyes): Round shape.

    • Nasal Cavity: Flared nasal opening; wide cheekbones; oval nasal opening.

    • Prognathism: Variable.

  • European Lineage:

    • Orbits (Eyes): Sloped downwards ("aviator" shape).

    • Nasal Cavity: Narrow/teardrop nasal opening; large, prominent nasal spine; steepled nasal silling.

    • Prognathism: Flat profile.

Biological Sex Determination

• Prerequisites: Determination of sex can only be accurately performed if the deceased has passed puberty.

• General Frame: Female frames and bones are typically more slender than male frames.

• Primary Diagnostic Bones: The skull and the pelvis are used, though the pelvis is the most reliable bone for sex determination.

• Skeletal Differences in the Skull:

  • Mandible: Male (square); Female (V-shaped).

  • Eye Orbits: Male (more square); Female (more rounded).

  • Brow Ridge: Male (thick and robust/large); Female (thin and slender/gracile).

  • Occipital Protuberance: Male (prominent); Female (less prominent).

  • Frontal Bone: Male (low and sloping); Female (higher and more rounded).

  • Surface of Skull: Male (rough/robust); Female (smooth/gracile).

  • Zygomatic Process (Cheekbone): Male (extends to ear opening or past it); Female (stops short of ear opening).

  • Mastoid Process: Male (larger/more robust); Female (smaller).

• Skeletal Differences in the Pelvis:

  • Subpubic Angle: Male (usually less than $90^{\circ}$ or < 90^{\circ}); Female (greater than $90^{\circ}$ or > 90^{\circ}).

  • Pelvic Cavity Shape: Male (heart-shaped); Female (oval or flattened oval).

  • Sacrum and Tailbone: Male (longer tailbone, sacrum curved inward); Female (shorter tailbone, sacrum curved outward).

  • Hips (Ilium): Female features a rectangular pubis and a wider ilium.

Estimating Age at Death

• Accuracy: The younger the individual (with fetuses being the most accurate), the more narrow and precise the age range estimation.

• Cranial Suture Closure:

  • Sagittal Suture: Closes at age $32$.

  • Lambdoidal Suture: Begins closing at age $21$, accelerates at $26$, and closes around age $30$.

  • Coronal Suture: Closed at approximately age $50$.

  • Squamosal Suture: Begins closing after age $60$.

• Ossification of Bones (Estimation Guidelines):

  • Arm: Humerus cap bones fuse at ages $4-6$; humerus cap fuses to shaft at ages $18-20$.

  • Leg: Femur head fuses to shaft at ages $16-18$; condyles join shaft at age $20$.

  • Shoulder: Clavicle and sternum close at ages $22-30$.

  • Pelvis: Pubic bone and ischium unite at ages $7-8$; ilium, ischium, and pubic bones fully ossify at ages $20-25$.

  • Sacrum: All segments unite at ages $25-30$.

• Odontology (Teeth):

  • Age can be estimated based on the eruption and loss of baby teeth vs. adult teeth.

  • Example eruption (Adult): Central Incisor ($7.35\text{ years}$), First Molar ($6.30\text{ years}$), Third Molar ($17-21\text{ years}$).

Forces and Trauma Analysis

• Terminology: Experts infer cause of death; they typically state that observed trauma is "consistent with" a specific event.

• Five Types of Bone Force/Injury:

  1. Compression: Force pushes down. Resulting fractures are simple lines. Common in skull/chest. Often associated with Blunt Force Trauma where the bone displacement matches the instrument shape.

  2. Shearing: Occurs via the immobilization of one bone segment. Often caused by falling or dismemberment. Characterized by vertical shear fractures.

  3. Bending: The most common type of force. Impacts occur at right angles. This type of trauma often implies a violent struggle. One subtype is the Greenstick fracture, which is common in children because their bones have more organic matrix and are more flexible.

  4. Torsion: A twisting force. Commonly associated with accidents (e.g., snowboarding) or child abuse. Results in Spiral fractures or Epiphyseal fractures where the epiphysis separates from the diaphysis.

  5. Tension: A pulling force. Often associated with dislocations, accidents, or violent struggles.

• Classifications of Trauma:

  • Blunt Force Trauma: Affects a wide surface area of bone. Fracture lines are usually simple. Healed trauma shows depressed areas and circumferential fractures with smooth, rejoined edges.

  • Projectile Trauma: Wounds exhibit complete displacement (removal) of bone material and are accompanied by radiating fracture lines.

  • Sharp Force Trauma: Injury with a narrow focus. Results in puncture wounds or grazing cut marks depending on the angle of force.

  • Strangulation: Result in a broken hyoid (throat) bone in approximately $34\%$ of cases. This is difficult to determine in children as their throat bones have not yet fused.

Evidence Collection and Skeletal Analysis Methods

• Collection Procedures:

  • Remains are often incomplete.

  • Bones are dried and sometimes coated in an acrylic mixture to ensure preservation.

  • Storage must be in a climate-controlled environment.

  • Recovery from soil requires soft brushes and dental picks to protect fragile bones.

• Analysis Methods:

  • Comparative Radiography: Imaging techniques such as X-rays are compared to antemortem records. Note: Bones are constantly being remodeled, so they may differ from old images over time.

  • Non-imaged Records Comparison: Use of medical records and notes regarding specific health conditions or surgical procedures.

  • DNA Analysis: Extracting nuclear or mitochondrial DNA from bone for identification.

  • Photographic/Video Superimposition: The image of a skull is superimposed over a photo or video to confirm identity.

  • Craniofacial Reconstruction: "Reconstructing" the facial features of an individual to create an approximation of their face for identification purposes.