Human identification and forensic anthropology

Human identification and forensic anthropology provide the scientific framework for establishing the legal identity of an individual—whether living, dead, or represented by skeletal remains—through the evaluation of biological and physical markers. This process focuses on building a biological profile by determining four key parameters: race, sex, age, and height (stature). Race is identified through skull measurements and specific dental features, such as the shape of the incisors. Sex determination is highly accurate when using the bones of the pelvis and skull, relying on physical markers like the width of the greater sciatic notch in the hip. Age is estimated by tracking the appearance and fusion of ossification centers (points where bone replaces cartilage) and by analyzing dental development, including specialized techniques like Gustafson’s method, which looks at age-related wear and tear on the teeth. Stature is reconstructed by measuring the length of long bones, such as the femur, and using mathematical formulas to calculate the total body height. The most definitive method of identification is dactylography (fingerprinting), as fingerprint patterns are unique to every individual and never change throughout life. Other unique body markers, such as lip prints (cheiloscopy) or the pattern of ridges on the roof of the mouth (rugoscopy), can also provide secondary proof of identity. Together, these scientific methods ensure that investigators can accurately identify human remains and satisfy the legal requirements needed to prove that a specific individual is the subject of a crime or investigation.

Identification is the process of establishing the individuality of a person, whether living or dead. In forensic investigations, identifying the "Big 4" (race, sex, age, and stature) provides the foundation for building a biological profile.

Corpus Delicti

The term corpus delicti refers to the "body of the offense" or the "essence of the crime." In the context of human identification, it typically refers to the recovery of human remains; however, legally, it encompasses the objective evidence that a crime has been committed (e.g., the recovered stolen property in a theft or the charred debris in an arson case).

Classification of Identification Methods

Identification methods are categorized based on their level of certainty and the biological traits they analyze.

• Dactylography: Considered a definitive method of identification. It is the only method that can reliably differentiate between identical (monozygotic) twins, as their fingerprint patterns differ despite identical DNA.
• Superimposition: A specialized technique involving the matching of a recovered skull with an antemortem photograph of a missing person using specific anatomical landmarks (e.g., nasion, canthus). It is primarily used as a negative value test to exclude a suspected identity.

Medicolegal Significance

Establishing identity is mandatory in cases of:

• Unidentified bodies or skeletal remains.
• Mass disasters (e.g., plane crashes, floods).
• Claiming inheritance or insurance benefits.
• Criminal cases involving absconding suspects or imposters.

Race and sex are the most reliable indicators in building a biological profile from skeletal remains.

Race Determination

Race is identified through a combination of dental and skeletal measurements, with the cranium and long bones providing the most definitive markers.

• Cephalic Index (Cranium):
  • Formula: Maximum breadth of skullMaximum length of skull×100\frac{\text{Maximum breadth of skull}}{\text{Maximum length of skull}} \times 100Maximum length of skullMaximum breadth of skull×100
  • Classification:
    • Dolicocephalic (70–74.9): Africans, Aryans (Indian).
    • Mesaticephalic (75–79.9): Europeans, Chinese (ICE mnemonic: Indian, Chinese, Europeans).
    • Brachycephalic (80–85): Japanese.
• Anthropometric Indices:
  • Brachial Index: Ratio of the radius to the humerus (Upper limb).
  • Crural Index: Ratio of the tibia to the femur (Lower limb).
  • Intermembral Index: Comparison of the upper and lower limbs.
• Dental Features:
  • Mongoloid: Shovel-shaped incisors, taurodontism (enlarged pulp cavity), and enamel pearls on premolars.
  • Caucasoid: Carabelli’s cusp on the maxillary first molar.
  • Negroid: Increased tooth size and extra cusps.

Sex Determination

The pelvis is the most accurate indicator of sex, as its morphology is adapted for the physiological requirements of childbirth.

• Ashley’s Rule of 149 (Sternum): A total sternal length (manubrium + body) > 149 mm is characteristic of a male, while < 149 mm is characteristic of a female.
• Hyrtl’s Law: In males, the body of the sternum is > 2x the length of the manubrium; in females, it is < 2x the length.
• Pre-auricular Sulcus: Often deeper in females as a result of pelvic changes during pregnancy.

Krogman’s Accuracy

The accuracy of sex determination from skeletal remains increases significantly as more components of the skeleton are analyzed together.

• Pelvis: 95% (Best single indicator).
• Skull: 90–92%.
• Long bones: 80%.
• Pelvis and Skull combined: 98%.
• Complete skeletal set: 100%.

Age Estimation and Ossification

Age estimation is determined through the systematic evaluation of fetal measurements, the appearance and fusion of ossification centers, and dental development.

Fetal age estimation

Fetal age is estimated primarily based on the crown to heel length (CHL) using mathematical rules.

• CHL calculation: CHL = crown rump length (CRL) × 1.5.
• Rule of Hasse (< 5 months gestation): GA = √CHL.
• Rule of Morrison (> 5 months gestation): GA = CHL / 5.

Ossification centers

The timeline of appearance and fusion of ossification centers provides a reliable marker for age from the intrauterine period through early adulthood.

Carpal bone appearance sequence: Capitate (2 months) → Hamate (3 months to 1 year) → Triquetral (3 years) → Lunate (4 years) → Scaphoid (5 years) → Trapezium/trapezoid (5–6 years) → Pisiform (9–12 years).

Dentition

Dentition is the most reliable marker for age estimation in children (mineralization) and remains useful in adults through secondary changes.

• Primary (deciduous) teeth (20): Eruption begins at 6 months (lower central incisor) and is completed by 24 months.
• Secondary (permanent) teeth (32): Eruption begins at 6 years (first molar) and is completed by 17–25 years (wisdom tooth).
• Mixed dentition period: Between 6 years and 11 years; the total number of teeth remains constant at 24.

Advanced estimation methods:

• Gustafson method (> 25 years): Evaluates six secondary changes (Mnemonic: APSRTC): Attrition, Paradentosis, Secondary dentin (2nd reliable), Root resorption, Transparency of root (most reliable), and Cementum apposition.
• Boyde method: Counting microscopic incremental lines; the neonatal line (appearing at day 2 or 3) is a sign of live birth.
• Stack method: Estimates age from the height and weight of the tooth.

Stature (height) can be estimated from skeletal remains using mathematical correlations between the length of long bones and total body height.

• Regression Formulae: The Karl-Pearson formula is a widely utilized statistical method for calculating height from skeletal measurements.
• Multiplication Factor (Mnemonic: FeTHUR): A simplified method where the length of a dry long bone is multiplied by a specific factor to estimate height.
  • Femur: 3.7 (Best single bone; accounts for ∼27% of height)
  • Tibia: 4.5
  • Humerus: 5.3
  • Ulna: 6.1
  • Radius: 6.5
• Measurement Tool: A Hepburn osteometric board is used to accurately measure the maximum length of long bones.

Dactylography, or the Galton system, is a definitive method of identification based on the unique and permanent ridges found on the fingertips. These patterns develop between the 12th and 24th weeks of intrauterine life and remain unchanged until decomposition.

• Primary Patterns:
  • Loop (60–70%): The most common pattern; ridges enter and exit from the same side.
  • Whorl (25–30%): Ridges form concentric circles.
  • Arch (5%): The least common pattern; ridges enter from one side and exit from the opposite side.
  • Composite: A mixture of multiple patterns.
• Core and Delta Analysis:
  • Loop: Contains 1 core and 1 delta.
  • Whorl: Contains 1 core and 2 deltas.
  • Arch: Contains 0 cores and 0 deltas.

Advanced Identification Techniques

Beyond basic patterns, specialized branches of dactylography analyze microscopic details for higher accuracy:

• Ridgeology: The study and comparison of individual ridge characteristics (minutiae).
• Poroscopy (Locard’s system): The study of the arrangement, size, and frequency of sweat pores along the ridges.
• Edgeoscopy: The study of the microscopic contours and edges of the ridges.

• Cheiloscopy: Identification based on lip prints (using the Suzuki classification).
• Rugoscopy (Palatoscopy): Identification based on the unique patterns of the palatal rugae on the anterior hard palate.
• Podogram: Identification based on footprints; particularly useful for identifying newborns in hospital settings.
• Bertillon’s Method (Anthropometry): An obsolete identification system based on 11 specific body measurements and photographs.

Forensic serology involves the identification and analysis of biological fluids (blood, semen, saliva) and tissues (hair, bone) to provide definitive evidence for human identification and crime scene reconstruction.

Identification of Blood Stains

The analysis of suspected blood stains follows a tiered approach, progressing from presumptive screening to confirmatory testing.

Identification of Seminal Stains

Seminal fluid identification is critical in sexual assault investigations. Evidence is preserved for up to 3 days (sperm) or 4 days (semen).

• Presumptive (Screening):
  • UV Light: Seminal stains exhibit characteristic fluorescence.
  • Acid Phosphatase (AP) test: Detects high concentrations of AP secreted by the prostate.
• Confirmatory (Microchemical):
  • Barberio test: Produces yellow needle-shaped crystals in the presence of spermine.
  • Florence test: Produces brown rhombic crystals in the presence of choline.
• Definitive: Microscopic visualization of motile or non-motile spermatozoa.

Forensic Hair Analysis

Hair is a resilient form of trace evidence used to determine species, body region of origin, and potential maternal lineage via mitochondrial DNA.

• Medullary Index Formula: Diameter of medullaDiameter of hair shaft\frac{\text{Diameter of medulla}}{\text{Diameter of hair shaft}}Diameter of hair shaftDiameter of medulla

Forensic DNA Analysis

DNA fingerprinting provides a unique biological profile that can definitively identify individuals, except in the case of identical twins.

• Preferred Samples:
  • Blood: Collected in EDTA tubes; stained cells should be air-dried and sent in paper envelopes.
  • Dental Pulp: The most protected source of DNA in decomposed or charred remains.
  • Skeletal/Muscle: Bone and deep muscle tissue in advanced putrefaction.
• Markers: Analysis typically utilizes Short Tandem Repeats (STRs) or microsatellites, which are highly polymorphic regions of noncoding DNA