Ridley writes that the switches controlling our 30,000 or so genes not only form the structures of our brains but do so in such a way as to cue off the outside environment in a tidy feedback loop of body and behavior. In fact, it seems clear that we have genetic 'thermostats' that are turned up and down by environmental factors. He challenges both scientific and folk concepts, from assumptions of what's malleable in a person to sociobiological theories based solely on the 'selfish gene.'

Ridley's proof is in the pudding for such touchy subjects as monogamy, aggression, and parenting, which we now understand have some genetic controls. Nevertheless, 'the more we understand both our genes and our instincts, the less inevitable they seem.' A consummate popularizer of science, Ridley once again provides a perfect mix of history, genetics, and sociology for readers hungry to understand the implications of the human genome sequence. --Therese Littleton