The chapter also discusses how, through reverse transcriptase, retroviruses like HIV copy themselves to the human genome. Simple determinism, whether of the genetic or environmental kind, is a depressing prospect for those with a fondness for free will. Because gene mutations (changes in the base sequence) often have two separate effects, one beneficial and one harmful.

Take the case of chromosome 4, which is home to the gene for Wolf-Hirschhorn syndrome, a rare and deadly disease that leads to early death, and to the gene for Huntington disease, which causes slow but certain neurological devastation in patients in mid-life.The reader is not left feeling like an insider to the world of science, but a very appreciative outsider.

For example, the chapter Fate, which I found the most fascinating, sought to prove that a good portion of our lives is written in our genetic code.Of course I haven't read Siddhartha Mukherjee's book, but I still suspect this book is better for the genetic novice. Suffice it to say that Ridley's talent for writing genetic science is not matched by his writing about current genomic science. An extraordinarily nimble synthesist, Ridley leaps from chromosome to chromosome in a handy summation of our ever increasing understanding of the roles that genes play in disease, behavior, sexual differences, and even intelligence.