Essential Forensic Biology
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Essential Forensic Biology

Alan Gunn

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Essential Forensic Biology

Alan Gunn

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A completely revised and updated edition that teaches the essentials of forensic biology, with increased coverage of molecular biological techniques and new information on wildlife forensics, wound analysis and the potential of microbiomes as forensic indicators

This fully revised and updated introduction to forensic biology carefully guides the reader through the science of biology in legal investigations. Full-colour throughout, including many new images, it offers an accessible overview to the essentials of the subject, providing balanced coverage of the range of organisms used as evidence in forensic investigations, such as invertebrates, vertebrates, plants and microbes. The book provides an accessible overview of the decay process and discusses the role of forensic indicators like human fluids and tissues, including bloodstain pattern analysis, hair, teeth, bones and wounds. It also examines the study of forensic biology in cases of suspicious death.

This third edition of Essential Forensic Biology expands its coverage of molecular techniques throughout, offering additional material on bioterrorism and wildlife forensics. The new chapter titled 'Wildlife Forensics' looks at welfare legislation, CITES and the use of forensic techniques to investigate criminal activity such as wildlife trafficking and dog fighting. The use of DNA and RNA for the identification of individuals and their personal characteristics is now covered as well, along with a discussion of the ethical issues associated with the maintenance of DNA databases.

  • Fully revised and updated third edition of the successful student-friendly introduction to the essentials of Forensic Biology
  • Covers a wide variety of legal investigations such as homicide, suspicious death, neglect, real and fraudulent claims for the sale of goods unfit for purpose, the illegal trade in protected species of plants and animals and bioterrorism
  • Discusses the use of a wide variety of biological material for forensic evidence
  • Supported by a website that includes numerous photographs, interactive MCQs, self-assessment quizzes and a series of questions and topics for further study to enhance student understanding
  • Includes a range of important, key case studies in which the difficulties of evaluating biological evidence are highlighted

Essential Forensic Biology, Third Edition is an excellent guide for undergraduates studying forensic science and forensic biology.

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Part I
Decay and the Discovery and Recovery of Human Remains

The Decay of Human Bodies

1.1 Introduction

The time before a person dies is the ante‐mortem period, whilst that after death is the post‐mortem period. The moment of death is the ‘agonal period’ – the word being derived from ‘agony’, because it used to be believed that death was always a painful experience. Either side of the moment of death is the peri‐mortem period, although there is no consensus about how many hours this should encompass. It is important to know in which of these time periods events took place in order to determine their sequence, the cause of death, and whether or not a crime might have been committed. Similarly, it is important to know the length of the post‐mortem period, referred to as the post‐mortem interval (PMI). This is because by knowing exactly when death occurred it is possible, among other things, to either include or exclude the involvement of a suspect. The study of what happens to remains after death is ‘taphonomy’ and the factors that affect the remains are ‘taphonomic processes’. Thus, burning, maggot feeding, and cannibalism are all examples of taphonomic processes.
When investigating any death, it is essential to keep an open mind as to the possible causes. For example, if the partially clothed body of a woman is found on an isolated moor, there are many possible explanations other than she was murdered following a sexual assault. First, she may have lost some of her clothes after death, through them decaying and blowing away or from them being ripped off by scavengers. Second, she may have been a keen rambler who liked the open countryside. Most people die of natural causes and she may have suffered from a medical condition that predisposed her to a heart attack, stroke, or similar potentially fatal condition whilst out on one of her walks. Another possibility is that she may have committed suicide: people with suicidal intent will sometimes choose an isolated spot in which to die. Another explanation for the woman's death would be that she had suffered an accident, such as tripping over a stone, landing badly, and receiving a fatal blow to her head. And, finally, it is possible that she was murdered. All of these scenarios must be considered in the light of the evidence provided by the scene and the body.

1.2 The Stages of Decomposition

After we die, our body undergoes dramatic changes in its chemical and physical composition and these provide an indication of the PMI. The changes also influence the body's attractiveness to detritivores (organisms that consume dead organic matter) and their species composition and abundance. These also act as indicators of the PMI. Furthermore, the post‐mortem events may preserve or destroy forensic evidence, as well as bring about the formation of artefacts. For example, the discharge of bloody fluids from the mouth and nose or the bluish discoloration of the skin, which are perfectly normal consequences of decay, can be mistaken for signs of assault or poisoning. An understanding of the decay process, and factors that influence it, is therefore essential for the interpretation of dead human and animal remains.
Animal decomposition in terrestrial environments can be divided into four stages: fresh, bloat, putrefaction, and putrid dry remains. However, these stages merge into one another and it is impossible to separate them into discrete entities. Indeed, bloat results from the process of putrefaction and therefore is dealt with as a sub‐section of putrefaction in this chapter. In addition, a body seldom decays in a uniform manner. Consequently, part of the body may be skeletonised, whilst another part retains fleshy tissue.

1.2.1 Fresh

Once the heart stops beating, the blood pressure drops and blood is no longer moved through the body. The blood within the vessels therefore settles under gravity to the lowermost dependent regions. Consequently, shortly after death, the skin and mucous membranes appear pale. Once the circulation ceases, tissues and cells no longer receive oxygen and nutrients and they begin to die. Different cells die at different rates, so, for example, brain cells die within 3–7 minutes, while skin cells can be taken from a dead body for up to 24 hours after death and still grow in a laboratory culture. Contrary to folklore, human hair and fingernails do not grow after death, although shrinkage of the surrounding skin makes it seem as though they do. Temperature Changes

Because normal metabolism ceases after death, our body starts to cool in a process known as algor mortis: literally, the coldness of death. For many years, measurements of body temperature were the principal means of determining the PMI. However, the technique suffers from a variety of shortcomings. To begin with, the skin surface usually cools rapidly after death and the mouth often remains open. Therefore, measurements recorded from the mouth or under the armpits would not reflect the core body temperature. In living persons, one way of determining core body temperature is with a rectal thermometer. However, this approach is not always appropriate in forensic cases. This is because inserting a rectal thermometer often requires moving the body and removing the clothing. This potentially interferes with evidence collection in cases where anal intercourse before or after death occurred.
Nowadays, the body temperature of living humans and many domestic animals is often determined from the temperature in the external auditory canal, measured using a custom‐designed electronic digital ear thermometer. This has the advantage of being quick, non‐invasive, and does not risk cross contamination or breakage of the thermometer in the body. The external auditory canal temperature correlates well with the brain temperature and it is useful for recording the temperature of dead bodies in hospital settings (Baccino et al. 1996). Unfortunately, in forensic scenarios, there are often complications that make the measurement of the ear temperature either difficult or the interpretation of the results questionable (Rutty 1997); for example, if the body is submerged or water enters the ear canal from rain or condensation, if there is bleeding into the ear canal following a skull fracture, and if there is traumatic damage to the ears from blows to the head.
A second major problem with using body temperature as a measure of the PMI is that the rate of cooling depends upon a host of complicating factors. These start with the assumption that the body temperature at the time of death was 37 °C. In reality the body temperature may be higher (e.g. owing to infection, exercise, or heat stroke) or lower (e.g. hypothermia or severe blood loss). In addition, the rate of temperature loss depends upon numerous factors (Table 1.1). For example, subcutaneous fat acts as an insulator that reduces the rate at which heat is lost from the body. Adult women tend to have a higher fat content than men, and therefore the bodies of a woman and a man of the same weight cool down at different rates. Similarly, the body of a fat man who dies inside a car on a hot sunny day may not lose heat to any appreciable extent; indeed, his body temperature may even increase.
Table 1.1 Factors affecting the rate at which a body cools after death.
Factors that enhance the rate of cooling
Small body size
Low fat content
Body stretched out
Body dismembered
Serious blood loss
Lack of clothes
Wet clothes
Strong air currents
Low ambient temperature
Rain, hail
Cold, damp substrate that conducts heat readily (e.g. damp clay soil)
Body in cold water
Dry atmosphere
Factors that delay the rate of cooling
Large body size
High fat content
Foetal position (reduces the exposed surface area)
Clothing – the nature of clothing is important because a thin, highly insulated layer can provide more protection than a thick poorly insulated material.
Insulated covering (e.g. blanket, dustbin bags, paper, etc.)
Protection from draughts
Warm ambient temperature
Warm microclimate (e.g. body next to a hot radiator)
Exposed to the sun
Insulated substrate (e.g. mattress)
High humidity
Various formulae relate body temperature to the length of time since death, but these are mostly too simplistic to be reliable. Clauss Henßge designed a sophisticated nomogram that accounts for body weight and environmental temperature and allows application of corrective factors according to the individual circumstances of the case (Henssge and Madea 2004). A nomogram is a graphical calculator that usually has three scales (Figure 1.1). Two of these scales record known values (rectal and environmental te...

Table of contents

Citation styles for Essential Forensic Biology
APA 6 Citation
Gunn, A. (2019). Essential Forensic Biology (3rd ed.). Wiley. Retrieved from (Original work published 2019)
Chicago Citation
Gunn, Alan. (2019) 2019. Essential Forensic Biology. 3rd ed. Wiley.
Harvard Citation
Gunn, A. (2019) Essential Forensic Biology. 3rd edn. Wiley. Available at: (Accessed: 14 October 2022).
MLA 7 Citation
Gunn, Alan. Essential Forensic Biology. 3rd ed. Wiley, 2019. Web. 14 Oct. 2022.