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Genes Don't Act Alone
The Dependent Gene: The Fallacy of ‘Nature vs. Nurture’
by David S. Moore

Reviewed by
Julie Buckles

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Glancing at the title of David S. Moore's latest book, readers might think as I did: Wasn't the 'nature vs. nurture' argument decided long ago? Haven't scientists already concluded that traits such as intelligence and athletic ability are a combination of both?

Perhaps. Certainly genomic tools have in recent years helped reveal the complex workings of the human cell, including interactions between genes and proteins in the cellular environment. But the message that environmental factors inside cells are important in affecting traits may not have reached the public.

Moore worries that the media coverage of studies linking individual genes to everything from homosexuality to obesity has persuaded people that we are no more than the sum of our genes. In The Dependent Gene: The Fallacy of "Nature vs. Nurture", Moore sets out to change the nature-nurture debate once and for all.

"The viewpoint offered in this book," he writes, "frees both individuals and society from the chains of genetic determinism…no longer will people have to bear the thought that their destiny and the destiny of their children is preordained in their genetic endowment and forever beyond their dominion."

‘All traits are caused by dependent interactions of genes and environments.’

Moore, who received his doctorate in developmental psychology from Harvard University and is now a professor of psychology at Pitzer College and Clarement Graduate University in Claremont, California, argues for equal billing for nature and nurture. As the title of the book implies, his central thesis is that genes (nature) depend on the environment (nurture) to express themselves, and that even traits we have assumed being genetic are influenced by environmental factors.

The book is broken into five sections, each with this one point to make: Genes never act alone. "All traits—from 'biological' traits like hair color and height to complex 'psychological' traits like intelligence—are caused by dependent interactions of genes and environments," says Moore (italics are his.)

Take hair color, taught in science classes across the United States as a genetic trait, inherited from mom or dad. There's more to it, says Moore. The presence of melanin determines hair colorlike eye and skin color. Melanin is formed as an end product during the normal biological breakdown of an amino acid called tyrosine. What affects the breakdown of tyrosine, also affects coloration.

With hair, the amount of natural melanin depends on concentrations of copper in the cells that are producing the hair—dark hair contains higher amounts of copper, lighter hair less. We get copper through our diets from such things as mushrooms, chocolate, shellfish, and nuts. "Hair color is not determined strictly by genetic factors," says Moore. "Diet is an environmental influence on hair color, even if circumstances render this influence relatively hard to see."

Diet also plays a central role in the development of PKU (short for phenylketonuria), a so-called genetic disease causing severe mental retardation in children. Children with PKU lack a gene responsible for breaking down phenylalanine-an amino acid we all consume in our diets (milk, eggs, meat, and bread). Phenylalanine accumulates in the children's bloodstream and urine, which eventually leads to mental retardation, seizures, tremors, and behavioral disorders.

Many states have adopted PKU testing for newborns. For those infants who test positive, doctors can modify their diet by restricting the phenylalanine intake. This significantly reduces the cognitive defects that characterize untreated PKU. Moore argues that even though PKU is widely considered to be a genetic disorder, "it in fact develops as a result of specific gene-environment interactions."

Moore limits his discussion of genetic diseases to a few like PKU that can be treated with dietary measures, while omitting single-gene diseases like Huntington's or Tay Sachs, which cannot be treated by changing factors in one's environment. Omissions like these, combined with Moore's affinity for italicizing entire sentences, add to the argumentative feel of the book.

By the end, I found myself more confused than convinced. Moore complains, with some validity, about "the tendency of journalists to excitedly report not-yet-proven associations between traits and genes." Though he makes a well-meaning effort to clarify a complex area of biology, his treatment of the material is unlikely to serve as a primer for the general public.

Moore, David S. The Dependent Gene: The Fallacy of "Nature vs. Nurture". Times Books, New York, NY, 2001.

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