23 Differentiation of Animal and Human Hair

Introduction

Presence of hair on skin is unique feature of human beings. Each hair consist of the part within the follicles the hair root and shaft projecting the body surface. The hair is nourished by a hair follicle. Hair follicle produced keratinized cell which push the shaft from below and spread the oily secretion over the shaft. Due to such type of secretion hair is protected against adverse environment. Entire hair consist of three regions medulla in the middle, a thicker cortex around medulla and a delicate covering of cuticle which is made up of keratinous cells. Hairs are differentiated with characteristic length, color, shape and root appearance. Considerable variability also exists in the types of hairs that are found on the body. In humans, hairs found on the head, pubic region, arms, legs, and other body areas have characteristics that can determine their origin. Because hairs can be transferred during physical contact, their presence can associate a suspect to a victim or a suspect to a crime scene. The types of hair recovered and the condition and number of hairs found all impact on their value as evidence in a criminal investigation. Comparison of the microscopic characteristics of questioned hairs to known hair samples helps determine whether a transfer may have occurred. Hair evidence is very important because of the transference or exchange phenomenon. Hair samples are often critical clues to identifying the perpetrator of a broad range of crimes, including rape, burglary, assault, and vehicular homicide. Crimes such as burglary and armed robbery typically involve the recovery of debris and articles of clothing which may contain hairs useful for the identification of suspects. Hair is present on many different regions of the body. Each region, such as the head, pubic area, chest, axillae, and limbs, has hairs with microscopical characteristics attributable to that region. Although it is possible to identify a hair as originating from a particular body area, the regions of the body that are primarily used in forensic comparisons are the head and pubic areas. Physical contact may result in the transfer of hairs. These can transfer directly from the region of the body where they are growing or they can transfer from the clothing of individuals. These hairs are shed on clothing and on items in the environment. Contact between a victim and a suspect’s environment can easily cause a secondary transfer of hair. Hairs that are found on the clothing of suspects or victims and appear to have fallen out naturally may be the result of transfer. Hairs that have been forcibly removed may suggest a violent confrontation (Singh, 2014).

Human hair unquestionably figures as a clue or possible clue in a very considerable percentage of crimes, particularly those of violence, but only slightly less in crimes of stealth, since most individuals have a greater or fewer tendencies to lose hairs unconsciously and at random. It is indeed strange that so tempting a type of evidence should have been so indifferently treated by criminal investigators. Some criminologists have expressed confidence in their ability to determine the source of a hair, but usually without benefit of adequate study and by methods that are not generally known (Kirk, 1940).

Hair being the most common biological material found at the scene of crime, plays a crucial role in criminal investigations related to wildlife, taxonomy, Investigative dermatology, pathology and other applied fields of forensic science. As the growth is continuous from birth of an individual till death, there is constant loss and replacement of the hair strands spread over the body so they get transferred during the act of a crime. Its microscopic comparison and chemical analysis plays a very significant role other than blood and fingerprints. Hair is usually used to study characterisation of the known sample versus the questioned hairs recovered from the crime scene to check if they are from a common source for the establishment of a relation between crime and the criminal. Hair identification is done non invasively followed by invasive examination and it provides very precise results along with other relevant information about the suspect and proves its utility over other evidences in the detection of drugs, other illegal substances along with the information of habits and geographical region. Presently it is a widely accepted tool to identify the age, sex, colour, race, disease profile, diet, occupational and environmental exposure, metal poisoning, geographical indicator, illegal wildlife trade, sexual assault, rape, disputed maternity and paternity matters and in cases of mitochondrial DNA examination where the questions are raised related to evolution and inheritance. Hair also provides the information related to the poisonous or toxic substance that may have been linked to health or problems in psychological, re-productive disorders and in developmental toxins (Aparna and Yadav, 2013). Hair is always considered to be associative evidence and its ultimate objective being to associate a suspect and the victim in the act of crime supported by evidences based on the scientific approach and the crime scene scenario.

General structure of Hair

Hair is a fibre, thin structure approximately around 0.1mm in diameter with an oval or a circular cross- section. It is mainly composed of three concentric regions i.e. the outer layer being the cuticle which is a thin coating covered by tilted scales; the main constituent being cortex contributing to almost 90% of the total weight of the hair made up of differently shaped cells specific to the hair type and, the keratin fibres are arranged in a honeycombed arrangement of cell structure containing air pockets continuously or discontinuously, called the medulla. The follicle is the most active part which lies beneath the skin surface producing keratin proteins and the hair shaft collectively make up the hair strand. The follicle associated with the hair shaft acts as a mould to shape the strand. The hair shaft is stiff to a greater extent that helps reduce damage caused due to shear and stress in the strand. The frictional behavior is mainly linked to the cuticle which along with the cortex also determines the tensile strength and smoothness of the hair Condensation of alpha amino acids in the hair are bound together in same plane. Hair fibre is not uniform in composition and it is made up of both crystalline and amorphous regions. The segment of hair that captures the X-ray photograph of the keratin content is found to be around 20% and 80 % crystalline and amorphous respectively in nature. The keratin fibre is chemically composed of two forms i.e., α-keratin and β-keratin. The α form tends to remain folded but when it is stretched, it corresponds to the β-keratin form.

Type of Humans Hairs

Head and body hair of humans is classified as intermediate hair combining the characteristics of bristle and wool hairs. Four types of hair appear on the bodies of humans:

1) Primordial Hairs appear as early as the 3rd month of gestation, growing on the upper lip, the eyebrows, the palms and soles of the fetus. They gradually disappear and are replaced by softer lanugo hair over the entire body.

2) Lanugo Hairs are normally shed after the 6th month of gestation. They are fine, soft, unmedullated, and normally unpigmented hairs. The surface of lanugo hair is smooth with almost indiscriminate scales. It is replaced by vellus and terminal hairs. Lanugo Hair is often observed on an aborted fetus and can be useful in investigation of possible infanticide.

3) Vellus Hairs are the fine, soft, unmedullated hairs spread uniformly over the body surface. They rarely are more than 2 cm in length.

4) Terminal Hair is found on the scalp, eyebrows, eyelashes, and, to a lesser extent, the limbs of both sexes. Puberty is accompanies by pubic and axillary hair growth such as hair of the face, chest, back, arms, and legs. The various terminal hair types can be distinguished by density and morphology (Katz, 2005).

Type of Hairs in Animals

There are three types of hair usually found in animals:

1) Vibrissa: These are the whiskers of many animals. They are normally tactile and sensitive, such as the whiskers on a cat.

2) Bristle: This is the coarse bristle that provides an animal with a protective coat. These guard hairs can readily be identified by their distinctive appearance and morphology between various animal families.

3) Wool: Wool or fur provides insulation from wet and cold. These fine hairs cover the bodies of all mammals (Katz, 2005).

According to Deedrick and Koch (2004) animal hairs can be classified into three major groups on the basis of their microscopic appearance.

i) Deer family and antelope

ii) Commercial fur animals

iii) Domestic animals

For individual identification in these groups, deer family and antelope hairs are distinguished on the basis of their scale patterns, whereas commercial fur animals are distinguished on the basis of their color, color bands, scale patterns, and medullary structure. Domestic animals are distinguished primarily through their root structure, medullary structure, and pigmentation.

1) Deer family and antelope : Characteristics are –

a) Very coarse overall diameter (approximately 300m)

b) Medulla composed of spherical cells that occupy entire hair

c) Diameter constant throughout most of hair

d) Wineglass-shaped root

e) Regular wave or crimp

f) Commercial fur animals

2) The commercial fur Animals: this group includes several specimens commonly encountered in fur garments that are distinctive in their microscopic appearance. These are rabbit, seal, mink, muskrat, and chinchilla. Of these, seal and chinchilla are identified on the basis of the appearance of their down or fur hairs, not by their guard hairs. This is because guard hairs are frequently plucked from seal pelts for a more pleasing appearance. Chinchilla pelts have few, if any, guard hairs. The remaining specimens in the commercial fur group are identifiable largely by their characteristic colors and color banding. Characteristics are –

a) Very fine to medium overall diameter (20 to 150μ)

b) Characteristic medullary formations (serial or vacuolated)

c) Wide diameter variations in single hair

d) Hairs generally banded

3) Domestic animals: There are wide variations in color and length of the hair specimens in the domestic animal group. The identifying characteristics given are general and apply in most cases. In order to distinguish between dog and cat and between beef (cattle) and horse, it is usually necessary that the root be present. Characteristics are-

a) Medium overall diameter (75 to 150μ)

b) Medulla generally amorphous

c) Moderate diameter variation in single hair

d) Hairs generally unbanded

The pigmentation of animal Hair Fibre

Melanin is mainly responsible for the many shades of black, brown and other shades of hair and is found in the form of granules which are seldom uniformly distributed in fibre or in crimpy fibres the pigmentation is asymmetrical (Ancans et al, 2001). More pigmentation is observed in paracortex than orthocortex, this asymmetrical distribution of granules is originated by differential allocation of melanocytes inside the follicular bulb where the fibre is formed (Bell et al, 1967). Electron microscopy of the melanin granules revealed their egg-shaped bodies; the ratio varies in major and minor axis with the origin of granules. The Pigments get deposited over the layers of the granules in hair made up of layers formed of proteins (Stan & Paus, 2001; Harrison & Sinclair, 2003). Electron micrographs showed the axis of granules tends to lie parallel to the axis of cortical cells, and granules are arranged end to end on rows covered by fiblillar keratin (Franbourg et al, 2003; Tobin and Paus, 2001; Slominski et al 1996; Lindner et al 2001). Melanin is chemically inert in nature and are polymers of high molecular weight and known to be formed due to the action of tyrosinase to yield indole-5- 60quinone which then polymerizes. Several researches have revealed that natural melanin show close association with metals, especially iron and with proteins (). Thus, pigmentation of hair can serve as important parameter for differentiation of animal hair from human hair (Dahiya and Yadav, 2013).

Differentiation in Animal and Human Hair

a) Human hairs are generally consistent in color and pigmentation throughout the length of the hair shaft, whereas animal hairs may exhibit radical color changes in a short distance called bandi The distribution and density of pigment in animal hairs can also be identifiable features. The pigmentation of human hairs is evenly distributed, or slight ly more dense toward the cuticle, whereas the pigmentation of animal hairs is more centrally distributed, although more dense toward the medulla.

b) The medulla, when present in human hairs, is amorphous in appearance, and the width is generally less than one-third the overall diameter of the hair shaft. The medulla in animal hairs is normally continuous and structured and generally occupies an area of greater than one-third the overall diameter of the hair shaft.

c) The root of human hairs is commonly club-shaped, whereas the roots of animal hairs are highly variable between animals.

d) The scale pattern of the cuticle in human hairs is routinely imbricate. Animal hairs exhibit more variable scale patterns. The shape of the hair shaft is also more variable in animal hairs (Deedrick and Koch, 2004).

Three Main Difference in Human and Animal Hair

Conclusion

The hairs from the questioned source exhibit the same microscopic characteristics as the hairs in a known hair sample and can be associated to the source of the known hairs and others of similar breed i.e. it is stated that the questioned hairs can be associated with the source of the known hairs. Hairs are biological specimens and subject to variation. During the analysis of hair, the examiner must establish the range of variation in the sample and then determine whether the questioned hair fits in that range. The possibility cannot be dismissed that there may be two hair samples whose ranges of variation overlap and distinguishing between the samples is not possible. The hairs from the questioned source are microscopically dissimilar to the hairs in a known hair sample and cannot be associated with the source of the known hairs. The questioned hairs exhibit both similarities and slight differences to hairs found in a known hair sample, and no conclusion can be reached whether they could have originated from the known source. It may be that, in the opinion of the examiner, the differences are not sufficient to eliminate the source of the known hairs as being a possible source of the questioned hairs. At the same time, the presence of these differences precludes an association being made between the questioned and known hairs (Deedrick and Koch, 2004).

Summary:

Hair can be important physical evidence at a crime scene. The morphological examination routinely involves a two-step process involving a comparison microscope — (i) the identification of questioned hairs and (ii) the comparison of questioned and known hairs. During comparison, length of the hairs as well as a maximum number of microscopic features is considered. This associative evidence is particularly useful in crimes of violence where physical contact may have occurred, such as homicide and sexual assault. Crimes such as burglary and armed robbery typically involve the recovery of articles and clothing, which may contain hairs that are useful for the identification of suspects. Difference can be done through consistent in color and pigmentation throughout the length of the hair shaft, whereas animal hairs may exhibit radical color changes in a short distance called banding. The distribution and density of pigment in animal hairs can also be identifiable features. The pigmentation of human hairs is evenly distributed, or slightly more dense toward the cuticle, whereas the pigmentation of animal hairs is more centrally distributed, although more dense toward the medulla. The medulla, when present in human hairs, is amorphous in appearance, and the width is generally less than one-third the overall diameter of the hair shaft. The medulla in animal hairs is normally continuous and structured and generally occupies an area of greater than one-third the overall diameter of the hair shaft. The root of human hairs is commonly club-shaped, whereas the roots of animal hairs are highly variable between animals. The scale pattern of the cuticle in human hairs is routinely imbricate. Animal hairs exhibit more variable scale patterns. The shape of the hair shaft is also more variable in animal hairs.

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