This new vanguard is a loose-knit group of geneticists, neuroscientists, cognitive psychologists, and others, some of whom call themselves developmental systems theorists. I call them interactionists because of their emphasis on the dynamic interaction between genes and the environment. Not all of the interactionists’ views have yet been fully accepted, and they freely acknowledge their ongoing struggle to articulate the full implications of their findings. But it already seems very clear that these implications are far-reaching and paradigm-shifting.
To understand interactionism, you must first try to forget everything you think you know about heredity. “The popular conception of the gene as a simple causal agent is not valid,” declare geneticists Eva Jablonka and Marion Lamb. “The gene cannot be seen as an autonomous unit—as a particular stretch of DNA which always produces the same effect. Whether or not a length of DNA produces anything, what it produces, and where and when it produces it may depend on other DNA sequences and on the environment.”
Though Mendel couldn’t detect it with his perfectly calibrated pea-plant hybrids, genes are not like robot actors who always say the same lines in the exact same way. It turns out that they interact with their surroundings and can say different things depending on whom they are talking to.
This obliterates the long-standing metaphor of genes as blueprints with elaborate predesigned instructions for eye color, thumb size, mathematical quickness, musical sensitivity, etc. Now we can come up with a more accurate metaphor. Rather than finished blueprints, genes—all 22,000 of them—are more like volume knobs and switches. Think of a giant control board inside every cell of your body.
Many of those knobs and switches can be turned up/down/on/off at any time—by another gene or by any minuscule environmental input. This flipping and turning takes place constantly. It begins the moment a child is conceived and doesn’t stop until she takes her last breath. Rather than giving us hardwired instructions on how a trait must be expressed, this process of gene-environment interaction drives a unique developmental path for every unique individual.
The new interactionists call it “GxE” for short. It has become central to the understanding of all genetics. Recognition of GxE means that we now realize that genes powerfully influence the formation of all traits, from eye color to intelligence, but rarely dictate precisely what those traits will be. From the moment of conception, genes constantly respond to, and interact with, a wide range of internal and external stimuli—nutrition, hormones, sensory input, physical and intellectual activity, and other genes—to produce a unique, custom-tailored human machine for each person’s unique circumstance. Genes matter, and genetic differences will result in trait differences, but in the final analysis, each of us is a dynamic system, a creature of development.
Excerpted from The Genius in All of Us: Why Everything You’ve Been Told About Genetics, Talent, and IQ Is Wrong by David Shenk. Copyright © 2010 by David Shenk. Excerpted by permission of Doubleday, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher. Read an interview with David Shenk.