| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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Counterpoints in science Three Dot Science In this season when all San Francisco is honoring Herb Caen on his 80th birthday, I've collected some short scientific items and strung them together with the columnist's three dots. . . If you think that large-scale atmospheric pollution has been going on for only a couple of centuries, you're off by about 2,300 years. Smog started 2,500 years ago with the crude smelting technologies used for copper production during Roman and medieval times. French and American researchers have studied the copper concentrations in Greenland ice cores going back seven thousand years. The first bunp up, to about twice the natural level, occurred about 500 B.C., and copper in the ice has been rising ever since. Now it's eight times what it was then (Science April 12, 1996)... One of the weirdest cases I encountered as an intern at Stanford was a ten-year-old boy with a heart attack. The kid looked like a little old man, with wrinkles and gray hair, and he had the coronary arteries of a man of 75. This condition is called progeria, and until a few months ago its cause was unknown...One type of progeria, known as Werner's Syndrome, is now revealed to be due to defective DNA metabolism. The DNA of normal persons slowly accumulates abnormal mutations, which aggravate age-related diseases like cancer, diabetes, heart attacks, and brain deterioration. In Werner's Syndrome, DNA undergoes more rapid mutations, which bring on the diseases of old age while the victim is still young. This discovery could help us understand normal as well as premature aging (Science April 12, 1996)... Prions are abnormal proteins responsible for transmitting degenerative brain disorders such as "mad cow disease," scrapie in sheep, and Creutzfeldt-Jakob disease in humans. A normal form of the prion protein exists in all nerve cells, but its function is unknown. The "prion diseases" are probably due to loss of insulin...Researchers have recently created transgenic mice that lack prion protein, proving that animals can live without this mysterious stuff. However, the mice's sleep cycles and daily rhythms are disturbed, like humans with a rare inherited prion disease called fatal familial insomnia. No "mad mouse disease" has turned up as yet... The fear of "mad cow disease" may have destroyed the British beef industry, because ten out of the millions of beef-eaters have contracted a form of Creutzfeldt-Jakob disease that may or may not have come from beef. Hordes of Europeans are stampeding away from British beef, but about a third of these frightened comsumers continue to smoke, a habit that will kill millions of them. People prefer familiar risks to unfamiliar ones, even if the familiar hazzards are far more common and lethal. This paradox was pointed out by David Chapman in his recently published book Natural Hazards... We all know people who are afraid to fly and will drive long distances to avoid plane travel, through mile for mile flying is much safer than driving... And beach-loads of pale-skinned men and women bask in the blazing sun each summer day, creating an epidemic of skin cancer. In the past two decades, the death rate in men due to melanoma, the most malignant type of skin cancer, has increased by 48 percent, the highest sex-specific increase of all cancers... Sun exposure, particularly before the age of 18, greatly increases the risk of melanoma and other skin cancers, but less than a third of Americans, even as adults, limit their exposure to the sun, routinely use sunscreen, or wear protective clothing... As they lie on the beach baking, they worry about the long-term one-in-a-million risks from the trace pollutants in the air and water... "Why don't plants get cancer?" asked John Doonan and Tim Hunt in a recent issue of Nature. Plants, they pointed out, are remarkably resistant to developing malignancies and seem unscathed by their exposure to strong sunshine and ultraviolet light. Carcinogens stimulate the production of extra cells in animals, which may turn into tumors. Plants can also be induced to make extra cells, but unlike animals they incorporate these spare cells harmoniously into their roots or stems or leaves. . . In plants, cell identity is determined by the cell's position relative to its neighbors. A new cell formed in the root becomes a root cell. In animals, though, cell identity is determined by genealogy, not position. A malignant lung cell that travels to the liver will grow lung tumors in the liver rather than becoming another liver cell. . . Some of our most potent anti-cancer drugs, such as taxol, have been discovered in plants. It seems that plants have a lot to teach us about combating malignant diseases. Some people talk to their plants.Maybe we should be listening instead... Did you know that seat belts cause cancer and heart disease? We all know that "seat belts save lives" in automobile accidents. But strictly speaking, they don't save lives, they prolong lives. And many of those spared early deaths on the highway will survive to acquire the maladies of old age, of which cancer and heart disease are the most common... All of us carry a dictionary in our brain, but how and where the words are organized and stacked has been a matter of dispute. Evidence has been growing that words are stored in the brain's left temporal lobe, in distinct categories such as animals, furniture, fruits, and tools. Lesions in this part of the brain, due to strokes or injuries, can result in specific defects such as the inability to name living things, or to recall proper names or the names of birds. Recent research has pinpointed the location of some of these word-bins. A PET scan shows radioactive glucose concentrated in the part of the brain involved in mental tasks such as recalling names of objects. In this way animal names have been mapped to the inferior part of the left temporal lobe and names of tools to the posterior part (Nature April 11, 1996). . . Vertebrates and insects had a common ancestor about half a billion years ago. Sometime since then, one or the other got turned upside down, and its legs are on what used to be the other's back. Special clusters of genes determine the bodily architecture of each organism. The same developmental genes that cause the back to form in the fruit fly cause the belly to form in the frog, and vice versa, proving that these animals have truly gone their topsy-turvy evolutionary ways (Nature, July 20, 1995). In Franz Kafka's eerie story Metamorphosis, Gregor Samsa wakes up one morning to discover that he has been transformed into a giant cockroach. From the genetic point of view, he has indeed flipped over if not out. . . Two popular myths about foods are exploded in last June's Wellness Newsletter, put out by the University of California at Berkeley. Garlic is not as good, and MSG is not as bad, as most people believe. In numerous publications and old-wives tales, garlic has been credited with near-miraculous powers, such as preventing cancer, lowering blood pressure, and lowering cholesterol. Sales of garlic supplements have been taking off. Hundreds of studies carried out in the last decade have not really validated any of these claims. It's harder to test the ancient theory that garlic wards off vampires. . . The chemical that gives garlic its distinctive smell is allicin. It's formed only when the garlic clove is bruised or crushed, and it's destroyed by cooking, so to get the therapeutic benefit of allicin, if any, you have to eat your garlic raw. Many people love the flavor of garlic but find garlic breath in others obnoxious. By keeping people at a distance, garlic probably helps to prevent infectious diseases, even if it doesn't have much effect on other conditions. . . Monosodium glutamate (MSG), on the other hand, a simple flavorful salt that has been a staple of Asian cuisines for centuries, has been widely condemned recently as the cause of the "Chinese Restaurant Syndrome," a postprandial reaction that supposedly includes dizziness, nausea, indigestion, and life-threatening allergic reactions. But glutamate is an amino acid, present in dozens of foods, such as tomatoes, Parmesan cheese, peas, chicken, and corn, so it would be odd if a natural nutrient were really so hazardous. To investigate the question, the Food and Drug Administration commissioned a comprehensive study, which concluded that MSG is harmless for the great majority of people. A small number are sensitive to MSG, but only in huge doses much greater than those normally found in food. The American College of Allergy and Immunology did its own study, and concluded that MSG is not an allergen, that is, not a substance that causes allergies. . . A plate of pasta with Parmesan cheese and tomato sauce has more glutamate in it than wonton soup. . .Watch for the next popular food myth: Italian Restaurant Syndrome! And dot's dot for dotty science a la mode de Caen. . .
Jerold M. Lowenstein is professor of medicine at the University of California, San Francisco. jlowen@itsa.ucsf.edu |
Fall 1996
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