BOTH SIDES OF THE FENCE There have been several highly publicized— and subsequently debunked— genetically modified (GM) food scares ["Don't Eat Again Until You Read This," March]. The most recent involved a study claiming that Bt corn pollen might cause harm to the monarch butterfly. A subsequent study by the EPA revealed that this was not the case. With the world's population projected to top 10 billion within the next few decades, we will be forced to increase food production. To meet those needs without GM foods would require clear-cutting vast amounts of land to convert it for agricultural purposes. We need to balance the harm this would cause against the risks of using more efficient GM seed products.
Christopher Jung Alexandria, Virginia
If Round-Up Ready soybeans mean more Round-Up spraying, almost all creatures, great and small, potentially lose. And as mentioned in the article, Bt toxins may have catastrophic biological and economic effects on such unintended targets as organic farmers. Then there's that cherished myth that most human starvation is caused by a lack of food, despite the fact that most starving people are so poor that food and medicines are not sufficiently available to them at any price. Starvation is, after all, mainly caused by a lack of money and resources, not food.
Jonathan Davis, Ph.D. Mesilla Park, New Mexico
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HOLD YOUR HEAD UP Roger Seymour claims that a long-necked dinosaur would have required an impossibly large heart to hold its head erect [R&D;, March]. I grant that the heart would have been subject to considerable hydrostatic pressure when the dinosaur raised its head, but why should this be an objection to the upright posture? In any closed plumbing system, pump strength requirements do not depend on how high the fluid must be pumped or on the ambient pressure. Consider a water-filled garden hose leading from the discharge port of a lightweight pump back to the intake port of the same pump. Flow rate will be the same whether the hose lies flat in a loop or is strung up a 20-foot flagpole.
Bryce M. Hand Professor Emeritus, Geology Syracuse University Syracuse, New York
Roger Seymour responds: The siphon principle, suggested by the garden hose analogy, is flawed for two reasons. First, siphons require tubes that remain open when a negative pressure occurs inside. Flow stops in small blood vessels if the pressure becomes negative, so blood pressure in the head needs to be positive. Second, pressure energy at the base of the descending hose may be transferred through the pump and help raise water in the ascending hose, but this cannot happen in animals. The descending blood goes through the right ventricle to the lungs, where the pressure needs to be low. If the left ventricle cannot develop enough pressure by itself to support the column of blood above it, then blood flow to the head would stop completely.
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99.99 PERCENT PURE In "Wild Cats in Carolina" [March], Dave Wildt states that subspecies hybrids are useless for restocking. This would come as a surprise to the Peregrine Fund, not to mention hundreds of thousands of birders east of the Mississippi. The peregrine's removal from the endangered species list was the result of the collection and subsequent release of several subspecies of birds in the same area, which then interbred. There may be arguments against genetic diversity, but they seem more theological than scientific— that only "nature" can fit an organism to its niche. If this were so, invasive species like starlings and kudzu could never have found a toehold in the New World.
Stephen Bodio Magdalena, New Mexico
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