The misconceptions around genetics
Many people think that having one gene here or there is enough to cause diseases, but most of the book is showing how complicated genetics really is. Ridley goes as far as criticizing the Human Genome Project, explaining that the HGP is founded on a simplification. Ridley doesn't think there is such a thing as one universal genome, because animals are constantly evolving and changing.
The battle between the sexes
Although the drama between men and women seems deeply social and behavioral, Ridley says the real issues are genetic, since our hormones, our bodies, our personalities, and our temperament are all borne from our genetic code. This, along with the sexual arms race that drove the development of homo sapiens, helps to explain the way gender shaped our evolution.
The timelessness of life and death
Ridley takes a moment in chapter 14 to express the irony that over 50 billion generations of animal life have existed on earth, and DNA still works, all these years later. This means that although animals live and die, the genome has been immortal and eternal for billions of years. "Life" itself has been going on non-stop since its origination.
Intelligence and eugenics
Although some studies have found genetic factors that contribute to intelligence, that doesn't mean that the question of intelligence is solved. Ironically, people who understand genetics poorly are most likely to misuse eugenics for pointless goals. There is no way to perfectly read a gene code and determine what kind of a person the DNA will make. This is why Ridley opposes the compulsory sterilization of Down's Syndrome sufferers.
Politics
Because politicians aren't trained in science (typically speaking), there is a serious risk when it comes to public health, because scientists are competing against common misconceptions, and policy makers are subject to the same common misconceptions that everyone else is. He uses the sheep brain disease, scrapie, to make his point.
