Genes are far too complex to understand simply.
Ridley spends a significant portion of the book explaining scientific mechanisms that are unique to DNA. One gene does this, one gene does that, but also many genes are in a matrix with other genes. For instance, a person with Asthma usually has at least 15 separate genetic mutations that all factor together to make the disease we call "Asthma." This hyper-complexity leads Ridley to be concerned about public safety, because policy makers and their constituents are drawing conclusions from their over-simplified understandings about genes.
Free will versus determinism.
Although typically free will discussions are left for the philosophers and theologians, Ridley discusses the issues from a genetic point of view. Those who are in favor of modifying the human gene code (through Eugenics) would not be able to determine a person's fate except to the extent that they shape a person's existence. But Ridley notices that humans are shaped by nature AND nurture, and his view is that the future will be shaped by genetic engineering.
Ancestors and evolution.
The most difficult part of human life to fathom is that science indicates that we evolved from a common ancestor with chimpanzees. In other words, we are animals, subject to our genes, our bodies, our instincts, and what's even more interesting, our genetic ancestors might hold clues as to why we developed in one way instead of another. These issues are within the domain of "science," but needless to say, they stretch well into the domain of philosophy.
