History and Development of Forensic Biology

Forensic biology as a distinct discipline emerged in the early twentieth century on the back of Karl Landsteiner's 1901 discovery of the ABO blood group system. Within two decades, German and Japanese courts were using ABO typing to resolve paternity disputes, and by the 1930s, blood-grouping evidence was admitted in criminal trials in the United Kingdom, the United States, and parts of continental Europe. The discrimination power was limited: roughly 45 per cent of the world population has blood group O, so ABO typing could exclude a suspect but rarely provide strong positive evidence.

Through the mid-twentieth century, serologists expanded their toolkit. The MN blood group system (Landsteiner and Levine, 1927) added another layer of discrimination. Secretor status, the property of secreting ABO antigens into saliva and other body fluids, was shown to be inherited and detectable in dried stains by the 1930s, extending blood-group typing to semen and saliva evidence. Phosphoglucomutase (PGM) isoenzymes added a further discriminating marker from the 1960s onward. By the late 1970s, a skilled serologist working with a good-quality sample could test five or six independent genetic markers and arrive at match probabilities in the range of one in several hundred or one in a few thousand. That was genuinely useful but far short of the near-certainty that DNA profiling would later deliver.

The field's legal acceptance was also a product of this period. In England, courts admitted blood-typing evidence from the 1930s on, with judicial guidance specifying that the evidence could exclude a person but that a matching type was not proof of identity. In the United States, some states were slower to admit such evidence, and individual courts set their own thresholds for expert testimony until the Federal Rules of Evidence (1975) created a more structured framework, later refined by the Daubert decision in 1993.

In 1984, Alec Jeffreys and colleagues at the University of Leicester developed a method for producing individual-specific DNA patterns using restriction enzymes and Southern blotting. Jeffreys called the output a DNA fingerprint, a term that stuck in public discourse even though the scientific community preferred DNA profile. The method, formally called Restriction Fragment Length Polymorphism (RFLP) profiling, worked by cutting genomic DNA at specific sequences, separating the resulting fragments by size using gel electrophoresis, and detecting the pattern with radioactively labelled probes that bound to hypervariable minisatellite regions. Each person's pattern was highly distinctive.

The first forensic application came in 1985 when Jeffreys used RFLP profiling in an immigration case: a Ghanaian boy whose right of entry to the United Kingdom was disputed had his biological relationship to his mother confirmed genetically. The first criminal application followed in 1986. In the village of Narborough, Leicestershire, two teenage girls had been raped and murdered, in 1983 and 1986 respectively. Police asked Jeffreys to compare semen samples from both crimes. The profiles matched each other but did not match the prime suspect, a local man who had confessed to the 1986 murder. The confession was false. Police then ran what is believed to have been the world's first DNA mass screening, collecting blood from more than 4,000 local men. Colin Pitchfork, who had persuaded another man to give blood on his behalf, was eventually identified and convicted. His 1988 conviction stands as the moment forensic biology acquired its most powerful tool.

RFLP profiling had a significant practical limitation: it required a relatively large quantity of intact, high-molecular-weight DNA. A dried bloodstain smaller than a ten-pence coin often yielded no result. This constraint shaped early casework, concentrating DNA evidence on blood, semen, and tissue samples large enough to provide adequate template. The arrival of PCR transformed that constraint entirely.

Kary Mullis developed the polymerase chain reaction in 1983, a method for exponentially amplifying a specific DNA sequence using repeated cycles of denaturation, primer annealing, and extension. PCR meant that forensic laboratories could, in principle, obtain a profile from a single cell. The first PCR-based forensic method used the DQ-alpha (HLA DQA1) locus, a relatively simple polymorphism that provided limited discrimination but proved the concept. By the early 1990s, laboratories were multiplexing PCR to type several loci simultaneously.

Short Tandem Repeats (STRs) became the standard markers. STR loci consist of a short sequence motif (typically 2 to 6 base pairs) repeated in tandem. The number of repeats varies between individuals. PCR can amplify STR loci efficiently and the products are separated by capillary electrophoresis, producing peaks at precise sizes. Multiplexing across 13 to 24 loci yields match probabilities routinely stated as less than 1 in a billion for unrelated individuals. The UK's National DNA Database, established in 1995, was the first national forensic DNA database. The FBI's CODIS (Combined DNA Index System), launched in 1998, followed, and dozens of countries have established similar systems. CODIS uses 20 core STR loci as of 2017, enabling database searching across participating laboratories.

Court acceptance of STR profiling came rapidly in most jurisdictions once peer-reviewed validation studies accumulated. In the United States, the National Research Council's 1996 report on DNA evidence provided a framework for statistical interpretation that courts adopted. In India, the DNA Technology (Use and Application) Regulation Bill was introduced in 2018 and revised thereafter, reflecting ongoing legislative work to formalise the use of DNA databases while addressing privacy concerns under the Digital Personal Data Protection Act 2023. The European Union's Prum Convention (2005) established cross-border DNA database sharing among member states. The underlying science is the same; the legal frameworks governing access, storage, and expungement differ significantly.

Biological evidence encompasses any material of biological origin that may be relevant to a legal proceeding. The major categories are blood, semen, saliva, vaginal secretions, urine, sweat, skin cells (touch DNA), hair, bone, and teeth. Each category has distinct collection, preservation, and analytical requirements, and each degrades at a different rate under different environmental conditions.

Blood is the most frequently encountered biological evidence in violent crime. It contains nucleated white blood cells that yield nuclear DNA, and red blood cells that carry ABO antigens. Wet blood should be collected on sterile swabs, air-dried before packaging, and stored at low temperature. Dried bloodstains on porous substrates such as fabric or wood can survive for years in cool, dry conditions. Heat, humidity, and UV radiation accelerate degradation; a bloodstain left in direct sunlight in a tropical climate may be analytically useless within weeks. See Blood as Biological Evidence for detailed collection protocols.

Hair is biologically complex evidence. A hair with its follicle attached contains nuclear DNA and can be profiled by standard STR methods. A shed hair without a follicle (effluvium or catagen hair) contains mitochondrial DNA but negligible nuclear DNA, requiring mtDNA sequencing rather than STR profiling. Hair shaft morphology, including pigmentation, cross-sectional shape, medullary pattern, and cuticle scale pattern, was historically used for species identification and general population-group assessment, but microscopic hair comparison has been severely criticised as a forensic method after a systematic FBI review beginning in 2012 found that examiners had overstated conclusions in a large proportion of cases reviewed. Morphological assessment of hair should be treated as a preliminary screen, not a basis for individualization.

Bone and teeth are the most durable biological materials. In decomposed remains or mass graves, they may be the only source of biological evidence available. Teeth enamel protects the inner pulp tissue, preserving DNA for centuries under favourable conditions. Bone cortical regions are sampled by drilling or cutting, with the petrous part of the temporal bone now recognised as the single best source of ancient or degraded DNA because of its high density and mineral content. Both bone and teeth are primary evidence in forensic anthropology; the forensic biology laboratory provides the DNA profiling component while skeletal analysis provides age, sex, stature, and ancestry estimation. See Forensic Anthropology for skeletal analysis methods.

Every forensic DNA method depends on principles first established in basic cell and molecular biology. The human cell contains a nucleus housing 46 chromosomes organised as 23 homologous pairs, carrying approximately 3.2 billion base pairs of DNA encoding roughly 20,000 to 25,000 protein-coding genes. Between genes lie vast non-coding regions that contain the repetitive sequences, including STR loci and minisatellites, that are most useful for forensic identification precisely because they are highly polymorphic and under no functional selection pressure.

Outside the nucleus, each mitochondrion carries its own small circular genome of approximately 16,569 base pairs encoding 37 genes. A single cell may contain hundreds of mitochondria, each with multiple copies of the mitochondrial genome, giving a total of hundreds to thousands of mitochondrial DNA molecules per cell compared to exactly two copies of each nuclear chromosome. This copy number difference explains why mitochondrial DNA is recoverable from samples where nuclear DNA has degraded beyond detection. The hypervariable regions HV1 and HV2 of the mitochondrial control region are the primary targets for forensic mtDNA sequencing.

The practical implications for forensic biology are direct. Nuclear DNA supports individual identification to probabilities routinely exceeding one in a trillion for unrelated persons. Mitochondrial DNA supports identification by maternal lineage, not individual identity: all maternal relatives share the same mtDNA sequence and cannot be distinguished from each other. Y-chromosome analysis similarly tracks the paternal lineage through Y-STR and Y-SNP profiling. Understanding these inheritance patterns is essential for correct interpretation of evidence, particularly in cases involving family reference samples. For the molecular detail of DNA structure and replication, see Chromosomes, Genes and the Human Genome.

Next-generation sequencing (NGS), also called massively parallel sequencing, sequences millions of DNA fragments simultaneously. Applied to forensic STR profiling, NGS detects sequence variation within repeat units that capillary electrophoresis misses, increasing discrimination power and resolving mixtures more reliably. Applied to single nucleotide polymorphisms (SNPs), NGS enables forensic DNA phenotyping: prediction of externally visible characteristics such as eye colour, hair colour, and skin tone from a DNA sample, and ancestry inference. These methods are now in operational use in several countries, including the Netherlands and the United States, with legal frameworks for admissibility varying by jurisdiction.

Investigative genetic genealogy (IGG), applied most prominently in the identification of the Golden State Killer in the United States in 2018, uses DNA profiles from crime scenes to search consumer genealogy databases and then builds family trees to identify suspects. The method raises significant privacy questions and has prompted regulatory responses: in the United States, the Department of Justice issued guidelines in 2019 restricting IGG use to violent crimes and unidentified remains. European data protection law under the GDPR creates additional constraints on database access and retention.

The trajectory from ABO typing to genomic forensics reflects a consistent pattern: each technological advance has increased discrimination power, reduced sample requirements, and extended the range of evidence types that can be analysed. The challenges that remain are not primarily technical. Mixture interpretation, low-template sample contamination, and the statistical communication of probabilistic evidence to juries are the areas where the greatest improvements in practice are still needed. For the laboratory infrastructure that supports these methods, see Forensic Biology Laboratory Organisation. For the application of biological methods beyond human identification, see Forensic Biotechnology, Forensic Botany, and Wildlife Forensics.