Forensic Hair Analysis: Human and Animal Hair

1. Introduction

Hair is a common type of physical evidence found at crime scenes. Forensic analysis of hair can provide valuable insights into the identity of the individual or animal to whom the hair belongs. This post will discuss the structure of hair, the classification of hair into human and animal categories, the differences between human and animal hair, the biochemistry of hair, and the functions of hair.

2 Structure of Hair

Hair is composed of three main layers:

2.1.1 Cuticle

The cuticle is the outermost layer of hair, consisting of overlapping scales that protect the inner layers. The scales on the cuticle can be used to determine the direction of growth of the hair and can also provide information about the animal species from which the hair originated.

2.1.2 Medulla

The medulla is the innermost layer of hair, which may be continuous, discontinuous, or absent depending on the type of hair. The presence or absence of the medulla, as well as its size and shape, can be used to distinguish between human and animal hair.

2.1.3 Cortex

The cortex is the middle layer of hair, containing pigment granules (melanin) that determine the hair’s color. The cortex makes up the majority of the hair’s structure and is responsible for the hair’s strength and elasticity.

3. Classification of Hair

Hair can be classified into two main categories: human hair and animal hair.

3.1 Human Hair

Human hair is generally finer and has a longer growth cycle than animal hair. Human hair can be further classified based on its location on the body, such as scalp hair, pubic hair, and facial hair.

3.2 Animal Hair

Animal hair varies widely in terms of its structure and appearance, depending on the species of animal. Animal hair can be further classified based on the type of animal, such as mammal hair, bird feathers, and reptile scales.

4. Differences between Human Hair and Animal Hair

There are several key differences between human hair and animal hair that can be used to distinguish between them:

• Human hair generally has a finer texture and a longer growth cycle than animal hair.
• Human hair often has a medulla that is continuous or absent, while animal hair typically has a medulla that is discontinuous or fragmented.
• The scale pattern on the cuticle of human hair is generally more regular and uniform than the scale pattern on animal hair.
• The pigment granules in human hair are generally smaller and more evenly distributed than the pigment granules in animal hair.

5. Biochemistry of Human and Animal Hair

5.1 Biochemical Composition of Hair

Hair is primarily composed of a protein called keratin, which is made up of amino acids. The specific amino acid composition of hair can vary depending on the species of animal and can be used to distinguish between human and animal hair.

5.2 Amino Acid Composition of Hair

The amino acid composition of hair can be analyzed using techniques such as high-performance liquid chromatography (HPLC) and mass spectrometry (MS). The relative proportions of certain amino acids, such as cysteine and serine, can be used to differentiate between human and animal hair.

Amino Acid	Human Hair	Animal Hair
Cysteine	High	Low
Serine	Low	High
Proline	Low	High
Glycine	High	Low

6. Functions of Hair

Hair serves a variety of functions in both humans and animals:

• Protection: Hair provides a barrier against environmental factors such as sun, wind, and cold temperatures.
• Sensory: Hair follicles contain sensory nerve endings that can detect touch, pressure, and vibration.
• Thermoregulation: Hair helps to regulate body temperature by providing insulation and allowing for evaporative cooling.
• Communication: In animals, hair can serve as a means of communication through visual cues such as raised hackles or brightly colored feathers.

7. Summary

Forensic hair analysis is a valuable tool in criminal investigations, providing information about the identity of the individual or animal to whom the hair belongs. By examining the structure of hair, the classification of hair into human and animal categories, the differences between human and animal hair, and the biochemistry of hair, forensic experts can provide valuable insights into the origin and identity of hair evidence. While hair analysis alone may not provide definitive identification, it can be used in conjunction with other forensic techniques to build a stronger case.