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Toxin or Treatment? I enjoyed reading the article on Edward Calabrese's findings ["Is Radiation Good for You?" December]. Hormesis is a hot discussion topic around our agency. I would like to emphasize a couple of points that were not clear, although implied, in the article. People can be exposed to the same chemicals in the environment from many sources. If something is at very low levels in soil, for instance, it might also be present at low levels in air and water. We have to look at levels present in all ways people can come into contact with the chemical before deciding if the level is too low to be toxic. Also, we know very little about fetal toxicity, assuming the chemical moves from the mother to the fetus. A level that is safe to a fetus at one point during development might cause severe harm during another stage. For now, I think we all agree to use caution in deciding what a safe or helpful dose might be.

Gail Godfrey Agency for Toxic Substances and Disease Registry Atlanta, Georgia

I read with great interest Will Hively's article about hormesis. You are to be congratulated on publishing this, since it is not entirely politically correct. I was rather surprised and a little disappointed that the work of T. D. Luckey of the University of Missouri at Columbia was not recognized. Sometime in the early 1980s, Dr. Luckey wrote a monograph that listed at least 1,200 references to radiation hormesis. I believe it was published by the Chemical Rubber Publishing Company. Luckey was also the first to use the term hormesis to refer to the beneficial effects of low-level radiation.

Frederick H. Martens Plainfield, Illinois

Pathogen Paradox Susan Freinkel's article "If All the Trees Fall in the Forest. . . " [December] poses an interesting paradox without reaching a satisfactory conclusion. She gives evidence that tree pathogens, just like human pathogens, are assisted in their spread all over the world by our international travel and trade practices. This implies that the pathogens would not normally move so quickly or as far. Yet she quotes forest pathologist John Castello saying the current sudden oak death epidemic and previous tree epidemics are simply a matter of natural equilibrium and that we should not waste the effort to combat them. This is the paradox: Human pathogens that emerge and spread via human activity rouse titanic efforts by medical, political, and social groups all over the world. This has great implications for the way we decide to manage our living world. Do we need to draw a line between human and nonhuman victims?

Rachel Life Seattle, Washington

Cognition Ignition While I applaud the efforts of Bruce McCormick and the staff at the Brain Networks Laboratory at Texas A&M; University for tackling the daunting task of mapping the three-dimensional structure of the brain [Future Tech, December], this is only one piece of the problem of the bottom-up approach to modeling cognition. It's not enough to know how the neurons are interconnected; we must also know the electrochemical "weighting" of each synapse. It is this collection of weights that determines how each neuron accepts and ultimately processes the signals coming from all of the axons connected to it. All the inputs to a given neuron are not treated equally.

David R. Tribble Plano, Texas

Circular Reasoning I found "Circles of Life" [November] very interesting and thought-provoking, but it missed a number of critical issues. Certainly, global temperature is a critical element of sustaining life on Earth or a similar planet orbiting another sun. However, one must not underestimate the importance of our nearly circular orbit around the sun in making our planet habitable. For example, close approaches to the sun, even if of short duration, would bathe the planet in enormous doses of UV radiation. A brief solar input to the atmosphere would probably result in horrendous storms and perhaps huge tides. A highly elliptical orbit could result in slowing Earth's rotation (due to tidal effects as Earth passed close to the sun), such as has apparently occurred with Mercury. Finally, an elliptical orbit would probably destabilize the moon's orbit around Earth, which would most likely result in greater long-term climate variations. Thus, although another Earth in a highly elliptical orbit might be able to sustain some sort of life, it seems unlikely that it would support the complex ecosystems that now exist on this planet.

Philip J. Shaller Tustin, California

Hallowed Ground In his October review, "Dark Pilgrimage," Tim Folger writes of the Trinity site in New Mexico, "Long caravans of cars snake across a land where hunger, thirst, and Apaches once killed without mercy." Mr. Folger, however, fails to mention another kind of unmerciful killer from this territory: American soldiers. Indigenous men, women, and children were hunted and killed throughout the entire area. Their only crime was that they lived on land that inspired the avarice of a nation. Mr. Folger's somber reverie on the Trinity site asks us to remember the destructive powers of our tools. At the same time, we should also remember the destructive power of ideas when the tool is only a rifle.

Michael Wilson University of Wisconsin at Milwaukee

Pinker Revisited The view that personality and behavior are a complex interaction of genetics and experience ["The Blank Slate," October] is certainly supportable, but it is not particularly new. While pleading for moderation, Steven Pinker characterizes the social sciences with sweeping generalizations, such as "For much of the past century, psychology has tried to explain all thought, feeling, and behavior with a few simple mechanisms of learning by association." There are many individuals with extreme views, but the dogma he attributes to prior social research has not been as pervasive as he describes. Much of this excerpt seems to be a work of criticism more than an evenhanded examination of an aspect of science. That said, I appreciate Pinker's concluding plea that we should "examine claims about the mind objectively, without putting a moral thumb on either side of the scale."

John Graham Snohomish, Washington

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