The book devotes one chapter to each pair of human
chromosomes. Since one (unnumbered) chapter is required to discuss the
sex chromosomes, the final chapter is number 22. Ridley was inspired to adopt this model by
Primo Levi's book
The Periodic Table. ;Chapter 1, Life The first chapter begins with a quote from
Alexander Pope on the cycle of life. The very broad topic "Life" is also the topic of the chapter. Ridley discusses the history of the gene briefly, including our "
last universal common ancestor". ;Chapter 2, Species Ridley discusses the history of human kind as a genetically distinct species. He compares the human genome to
chimpanzees, and ancestral
primates. He also points out that until the 19th century, most scholars believed that there were 24 sets of genes, not 23 as known today. ;Chapter 3, History This chapter discusses the interplay between early geneticists, including
Gregor Mendel,
Charles Darwin,
Hermann Joseph Muller and
Francis Crick. ;Chapter 4, Fate
Huntington's chorea is used to discuss the use of a particular sequence on
Chromosome Four to cause traumatic health consequences. The search for the chromosomal source of this and other related diseases is discussed through the work of
Nancy Wexler, someone who may have inherited the gene but who turns to scientific work to study it in others. ;Chapter 5, Environment The concepts of
pleiotropy and genetic
pluralism are introduced. A brief history of the study of
asthma is used as the case study. Asthma is related to as many as fifteen different genes, many on
chromosome five. Specifically, this includes a change from
adenosine (A) to
guanine (G) at position 46 on the
ADRB2 gene. The ADRB2 gene is related to the control of bronchodilation and
bronchoconstriction. ;Chapter 6, Intelligence
Robert Plomin's announcement in 1997 of the discovery of "a gene for intelligence" on
chromosome 6 is the foundation for this chapter's lengthier discussion of the genetic basis for
intelligence. This included gene
IGF2R on the long arm of chromosome 6, which may also be related to
liver cancer. Ridley continues his premise in this chapter that the use of simple
genetic markers is inadequate to describe the complete function of the genome, or the causation of disease. ;Chapter 7, Instinct This chapter discusses whether the form and existence of
language has a genetic component. In particular, "
specific language impairment" is possibly related to a gene on
chromosome 7. Ridley discusses the scientific disagreement between Canadian linguist
Myrna Gopnik and others on whether this disorder relates to difficulties with
grammar formulation, or is a broader intellectual disorder. ;Chapter X and Y, Conflict protein, bound to the
double helix of DNA Ridley contemplates
evolutionary psychology using the genes
SRY on the
Y chromosome, and
DAX1 and
Xq28 on the
X chromosome. The theory of genetic conflict and evolution is debated using the rhetorical question, are we bodies containing genes, or genes in bodies? ;Chapter 8, Self-Interest
Richard Dawkins's concept of the "
selfish gene" is described by Ridley through a discussion of
retrotransposons. This includes the behavior of the
LINE-1 and
Alu transposons. Further, Ridley discusses the possible purposes of
cytosine methylation in development. The chapter also discusses how, through
reverse transcriptase,
retroviruses like
HIV copy themselves to the human genome. ;Chapter 9, Disease For chromosome 9, the book examines the discussion of the blood-typing genetic sequences. Namely, the
ABO blood groups and their impact on evolution are discussed. Other genes mentioned include
CFTR for
cystic fibrosis. Ridley concludes that the
Human Genome Project is largely based on the inaccurate belief that there is one single human genome. Proof that this is wrong comes from answering the question, which of the several choices of blood typing genetic sequence is selected, since each one has different disease-resistant and evolutionary consequences? ;Chapter 10, Stress The impact of stress on the human body is described starting with the creation of hormones by the
CYP17 gene on
chromosome 10. Ridley points out the relationship between
cholesterol,
steroidal hormones such as
progesterone,
cortisol,
aldosterone,
testosterone and
oestradiol. ;Chapter 11, Personality Ridley chooses the gene
D4DR which codes for the manufacture of
dopamine and is located on the short arm of
chromosome 11. Interactions between dopamine,
serotonin and other
serotonin neurochemistry are lightly covered. ;Chapter 12, Self-Assembly This chapter relates to how understanding the
genetic code matches models for
embryonic development among vertebrates. Ridley discusses
'gap' genes,
'pair-rule' genes, and
'segment-polarity' genes.
Homeotic genes and
Hox genes are described briefly.
Walter Gehring's discovery of the
homeobox set of codes in 1983 is related to an on and off
switch metaphorically. ;Chapter 13, Pre-History Ridley describes the relationship between the development of
Indo-European and other ancient
root languages and the classical
polymorphisms which map genetic frequencies in
Eurasia. The interplay between the
breast cancer genes
BRCA2 on
chromosome 13 and
BRCA1 on
chromosome 17 help to illustrate these larger concepts. Ridley also describes genetic studies of different types of peoples to isolate why people developed a mutation allowing adults to
digest lactase in adulthood. He concludes that since the
herding tribes of the world all evolved this mutation earliest, these people's genes adapted to their environment. This may sound like
Lamarck's tale of the
blacksmith's strong arms 'handed down' to his sons, but it is not. The controversial conclusion is that willed action can alter our evolutionary history and genetic composition, by changing the environment to which we have to adapt. ;Chapter 14, Immortality This chapter examines the so-called "immortality" of the genetic code - i.e. how is it that genetic code can remain as precise as it has been for 50 billion copyings since the dawn of life? Part of the answer is in the protein enzyme
telomerase, lying on
chromosome 14 and coded by the gene
TEP1. ;Chapter 15, Sex Ridley discusses two chromosome 15 genetic diseases,
Prader-Willi syndrome and
Angelman's syndrome: Prader-Willi inherited from the father, Angelman's from the mother, through sexual antagonism and the placenta's control by paternal genes. ;Chapter 16, Memory Ridley debates the old knowledge versus instinct problem, claiming that natural selection will be the explanation of the instinct for grammar, and noting that many animals including invertebrates can learn. All the same, he argues that the brain is controlled by genes and gene products. ;Chapter 17, Death The TP53 gene on chromosome 17 suppresses cancer cells, while oncogenes stimulate cell growth and can cause cancer if kept switched on, while TP53 can cause cancer when kept switched off. Other mutator genes like BRCA1 and BRCA2 contribute to breast cancer. ;Chapter 18, Cures
Recombinant DNA enabled genetic manipulation with restriction enzymes and a ligase. Genetic engineering has been highly controversial, especially in food production; it might, writes Ridley, one day be used in humans. ;Chapter 19, Prevention It might be possible to prevent or cure
Alzheimer's disease and
coronary heart disease. APO genes like APOE influence fat and cholesterol metabolism. The E4 allele of EPOE contributes to the plaque buildup of Alzheimer's.
Genetic testing may help patients take early preventative action. ;Chapter 20, Politics The sheep brain disease
scrapie appeared to be infectious but did not involve a microorganism. The disaster of
Creutzfeldt–Jakob disease in humans was found to be caused by the PRP gene which produces a
prion protein that aggregates into clumps, destroying brain cells. Ridley attacks the panicky handling of
prion disease outbreaks by governments. ;Chapter 21, Eugenics Eugenics a century ago, based on faulty knowledge of genetics, led to immoral actions by governments and the US Supreme Court, pushing through
compulsory sterilization of people such as those with trisomy 21 which causes
Down syndrome. Ridley discusses the conflict between society, in the form of the state, and the individual. ;Chapter 22, Free Will Ridley addresses the heated debate between
genetic determinism and freedom. Children are moulded both by their peers (other children) and by their genes. He argues that behaviour is in the short term unpredictable, but "broadly" predictable in the long term. ==Reception==