Science writer Francis (Why Men Won’t Ask for Directions, 2003) sets out to dethrone the notion that genes are the “directors” of the “plays” that are our lives, orchestrating our development and determining our risk for disease and sundry physical and behavioral traits.
Yes, genes are important, writes the author, but they are subject to regulation by forces that can turn them on or off, sometimes for a lifetime, sometimes across generations. These forces can come via the cell housing of the genes, other parts of the body or the environment, in each instance initiating the actions of chemicals that bind (or unbind) one or more parts of a gene, preventing (or activating) its transcription. This is an “epigenetic” process—epigenetics is the science that studies the ways in which DNA can undergo long-term regulatory changes that do not involve mutations of the genes themselves. To illustrate, Francis provides a dizzying array of examples, which can be distracting. Do we really need the entire plot of The Deer Hunter to explain how each character’s presumed early-life stress determines reactions to combat? The point is that stress, particularly chronic stress in utero, can reset an individual’s stress barometer to ultrasensitivity, with unhealthy long-term consequences. Other early-life examples include the effects of maternal malnutrition and the bizarre consequences, including shrunken testicles, resulting from long-term anabolic steroid use. But it’s not only hormones that affect gene regulation. Epigenetic processes can occur randomly and sometimes be reversed. There is also the phenomenon of imprinting, by which offspring can vary dramatically depending on whether the genes activated derive from the father or the mother. Emerging cancer studies also indicate that epigenetic events may spur progression as well as spontaneous remissions.
In his zeal, Francis provides a primer of a new science that will please some readers; others may want—and can expect—more in-depth accounts to come.