These days an educated human being must confront two big ways in which her life is determined by forces outside of her control. First, there are her genes, which control biological life; then there's her social and economic environment, which shapes her ideas, preferences, and personality. To understand the structure of our lives, we have to understand how our genes and our environments interact, which is why, for centuries, we've been having debates about "nature vs. nurture." Are we "blank slates," shaped decisively by our experiences? Or is each human being, as Shakespeare's Prospero puts it, "a born devil, on whose nature Nurture can never stick"?
Science is moving steadily beyond the dichotomy between genes and the environment, but in ways that are not widely understood. In Epigenetics, Richard C. Francis, a biologist turned science writer, summarizes what we know about how the environment affects your genes, and vice versa. Essentially, events in the larger world can turn individual genes on and off -- and your children can inherit those "epigenetic" changes.
This little guy is how the environment affects your genes.
Epigenetics isn't terribly complicated, but it is a step beyond what most of us learned in high school. To review: A gene is a kind of template, containing information used by your cellular machinery to manufacture proteins. A gene "for" a stress hormone, for example, contains information telling your cells how to manufacture that hormone. The gene has two sections: one contains the template, and the other is a kind of "control panel" that turns the gene on, starting protein synthesis, or turns it off, rendering it inactive. Individual genes are constantly turning on and off, depending on the signals that arrive from outside of the cell where they're located -- so a stress hormone gene, located in a cell in your pituitary gland, may be turned off most of the time, until chemical signals arriving from elsewhere in the brain turn it on, when you see an enraged bear, say, or prepare for battle. This process is called gene regulation.
Scientists used to think of gene regulation as a fluid, short-term process: Genes, they figured, were constantly turning on or off, like lights on a switchboard. But it turns out the opposite is also true. Genes can be regulated for very long periods. A gene turned off in the womb can remain deactivated for a lifetime -- which is why unborn children exposed to famine in the womb can suffer from obesity later in life. A single traumatic event can permanently regulate genes in our stress system -- which is how a period of intense stress during wartime can result in long-lasting, chronic disorders like PTSD. What's happening, exactly? Small proteins called methyl groups plant themselves on those genetic control panels, and never leave.
The real surprise, Francis explains, has been that these epigenetic changes can be passed on from parent to child. Most often they're passed on indirectly. Rats who are poorly parented as children, for instance, often undergo epigenetic changes making them into inattentive parents, who in turn inflict the same epigenetic changes upon the next generation. In some species of plants, the epigenetic settings are actually passed on directly, with the parental DNA -- meaning that a new plant can inherit the responses of its ancestors to the environment they share. The environment, in this case, reaches right down into our genes -- and our changed genes shape the environment for others.
Epigenetics explain all this in clear, no-nonesense prose, without resorting to the examples from The Simpsons which seem to plague most science books these days. (It's more inventive: One particularly excellent chapter explains epigenetic change through the body of the steroid-addled baseball player Jose Conseco, from his brain to his testicles.) According to Francis, epigenetics ought to change our thinking in two ways. First, it ought to demystify the interaction of genes and environment: that interaction is constant, substantive, and prolonged, not paradoxical. And second, it ought to make us rethink how genes fit into an organism as a whole. Genes are important, he argues, but they're not in charge; instead, "the executive function resides at the cellular level," where genes are turned on or off. They're just part of a system, in which events flow from higher levels of organization down to our cells, and then flow back up, changing our lives as a whole.
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Leon Neyfakh is the staff writer for Ideas. Amanda Katz is the deputy Ideas editor. Stephen Heuser is the Ideas editor.
Guest blogger Simon Waxman is Managing Editor of Boston Review and has written for WBUR, Alternet, McSweeney's, Jacobin, and others.
Guest blogger Elizabeth Manus is a writer living in New York City. She has been a book review editor at the Boston Phoenix, and a columnist for The New York Observer and Metro.
Guest blogger Sarah Laskow is a freelance writer and editor in New York City. She edits Smithsonian's SmartNews blog and has contributed to Salon, Good, The American Prospect, Bloomberg News, and other publications.
Guest blogger Joshua Glenn is a Boston-based writer, publisher, and freelance semiotician. He was the original Brainiac blogger, and is currently editor of the blog HiLobrow, publisher of a series of Radium Age science fiction novels, and co-author/co-editor of several books, including the story collection "Significant Objects" and the kids' field guide to life "Unbored."
Guest blogger Ruth Graham is a freelance journalist in New Hampshire, and a frequent Ideas contributor. She is a former features editor for the New York Sun, and has written for publications including Slate and the Wall Street Journal.
Joshua Rothman is a graduate student and Teaching Fellow in the Harvard English department, and an Instructor in Public Policy at the Harvard Kennedy School of Government. He teaches novels and political writing.