Chapter One
Genes 2.0
How Genes Really Work
... On their own, most genes cannot be counted on to directly produce specific traits. They are active participants in the developmental process and are built for flexibility. Anyone seeking to describe them as passive instruction manuals is actually minimizing the beauty and power of the genetic design.
So why do I have brown eyes like my mom and red hair like my dad?
In practical terms, there are many elementary physical traits like eye, hair, and skin color where the process is near Mendelian — where certain genes produce predictable outcomes most of the time. But looks can be deceiving; a simple Mendel-like result doesn't mean that there wasn't gene environment interaction. "Even in the case of eye color," says Patrick Bateson, "the notion that the relevant gene is the [only] cause is misconceived, because [of] all the other genetic and environmental ingredients." Indeed, Victor McKusick, the Johns Hopkins geneticist widely regarded as the father of clinical medical genetics, reminds us that in some instances "two blue-eyed parents can produce children with brown eyes." Recessive genes cannot explain such an event; gene-environment interaction can.
When it comes to more complex traits like physical coordination, personality, and verbal intelligence, gene-environment interaction inevitably moves the process even further away from simple Mendelian patterns.
What about single genetic mutations that predictably cause diseases such as Huntington's disease?
Single-gene diseases do exist and account for roughly 5 percent of the total disease burden in developed countries. But it's important not to let such diseases give the wrong impression about how healthy genes work. "A disconnected wire can cause a car to break down," explains Patrick Bateson. "But this does not mean that the wire by itself is responsible for making the car move." Similarly, a genetic defect causing a series of problems does not mean that the healthy version of that gene is single-handedly responsible for normal function.
Helping the public understand gene-environment interaction is a particular burden, because it is so enormously complex. It will never have the same easy, snap-your-fingers resonance that our old (misleading) understanding of genes had for us. Given that, the interactionists are lucky to have Patrick Bateson on their side. A former biological secretary to the Royal Society of London and one of the world's leading public educators about heredity, Bateson also carries a powerful symbolic message with his surname. It was his grandfather's famous cousin, William Bateson, who, a century ago, first coined the word "genetics" and helped popularize the earlier, simpler notion of genes as self-contained information packets that directly produce traits. Now the third-generation Bateson is helping to significantly update that public understanding.
"Genes store information coding for the amino acid sequences of proteins," explains Bateson. "That is all. They do not code for parts of the nervous system and they certainly do not code for particular behavior patterns."
His point is that genes are several steps removed from the process of trait formation. If someone is shot dead with a Smith &Wesson handgun, no one would accuse the guy running the blast furnace that transformed the iron ore into pig iron — which was subsequently transformed into steel and later poured into various molds before being assembled into a Smith & Wesson handgun — of murder. Similarly, no gene has explicit authorship of good or bad vision, long or short legs, or affable or difficult personality. Rather, genes play a crucial role throughout the process. Their information is translated by other actors in the cell and influenced by a wide variety of other signals coming from outside the cell. Certain types of proteins are then formed, which become other cells and tissues and ultimately make us who we are. The step-by-step distance between a gene and a trait will depend on the complexity of the trait. The more complex the trait, the farther any one gene is from direct instruction. This process continues throughout one's entire life.
Height can provide a terrific insight into the gene-environment dynamic. Most of us think of height as being more or less directly genetically determined. The reality is so much more interesting. One of the most striking early hints of the new understanding of development as a dynamic process emerged in 1957 when Stanford School of Medicine researcher William Walter Greulich measured the heights of Japanese children raised in California and compared them to the heights of Japanese children raised in Japan during the same time period. The California-raised kids, with significantly better nourishment and medical care, grew an astonishing five inches taller on average. Same gene pool, different environment — radically different stature. Greulich didn't realize this at the time, but it was a perfect illustration of how genes really work: not dictating any predetermined forms or figures, but interacting vigorously with the outside world to produce an improvised, unique result.
It turns out that a wide varied of environmental elements will affect the genetic expression of height: a single case of diarrhea or measles, for example, or deficiencies in any one of dozens of nutrients. In Western cultures of the twenty-first century, we tend to assume a natural evolutionary trend of increased height with each generation, but in truth human height has fluctuated dramatically over time in specific response to changes in diet, climate, and disease. Most surprising of all, height experts have determined that, biologically, very few ethnic groups are truly destined to be taller or smaller than other groups. While this general rule has some exceptions, "by and large," sums up The New Yorker's Burkhard Bilger, "any population can grow as tall as any other . . . Mexicans ought to be tall and slender. Yet they're so often stunted by poor diet and diseases that we assume they were born to be small."
Born to be small. Born to be smart. Born to play music. Born to play basketball. It's a seductive assumption, one that we've all made. But when one looks behind the genetic curtain, it most often turns out not to be true.
Excerpted from The Genius in All of Us 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.
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