Chapter 13: Species Identification

Species identification represents a foundational technique in forensic biology, particularly when determining whether biological evidence originates from human or non-human sources. This chapter examines the immunological and molecular approaches that enable forensic scientists to make these critical distinctions with high confidence and specificity. Antibody-based methods form the traditional cornerstone of species identification work, requiring careful selection of appropriate antisera such as anti-human antibodies and rigorous titration procedures to ensure that reactions target only the intended species while minimizing cross-reactivity with other biological sources. Immunochromatographic assays, commonly known as lateral flow tests, have revolutionized rapid screening protocols by detecting species-specific proteins like human hemoglobin and human Glycophorin A with speed and simplicity suitable for preliminary casework. Classical precipitation-based immunological techniques including double immunodiffusion assays—performed through ring assay and Ouchterlony assay methodologies—remain valuable confirmatory tools that visualize antigen-antibody binding patterns as precipitin lines, providing visual confirmation of species identity. Crossed-over electrophoresis extends these immunological approaches by combining electrical separation with immunological detection. Modern forensic casework increasingly incorporates molecular methods that offer superior specificity and can succeed even when biological material is degraded or scarce. DNA sequencing of mitochondrial markers provides definitive species identification through comparison with reference databases, while single-base primer extension targeting species-specific genes such as cytochrome b enables rapid molecular discrimination between human and animal sources. The chapter emphasizes how integrating both immunological and molecular approaches provides comprehensive species identification capability, allowing forensic laboratories to handle diverse evidentiary materials with confidence and reliability in casework contexts.