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How the Inca Leapt Canyons
By JOHN NOBLE WILFORD, The New York Times, May 8, 2007
CAMBRIDGE, Mass. — Conquistadors from Spain came, they saw and they were astonished. They had never seen anything in Europe like the bridges of Peru. Chroniclers wrote that the Spanish soldiers stood in awe and fear before the spans of braided fiber cables suspended across deep gorges in the Andes, narrow walkways sagging and swaying and looking so frail.
Yet the suspension bridges were familiar and vital links in the vast empire of the Inca, as they had been to Andean cultures for hundreds of years before the arrival of the Spanish in 1532. The people had not developed the stone arch or wheeled vehicles, but they were accomplished in the use of natural fibers for textiles, boats, sling weapons — even keeping inventories by a prewriting system of knots.
So bridges made of fiber ropes, some as thick as a man’s torso, were the technological solution to the problem of road building in rugged terrain. By some estimates, at least 200 such suspension bridges spanned river gorges in the 16th century. One of the last of these, over the Apurimac River, inspired Thornton Wilder’s novel “The Bridge of San Luis Rey.”
Although scholars have studied the Inca road system’s importance in forging and controlling the pre-Columbian empire, John A.Ochsendorf of the Massachusetts Institute of Technology here said, “Historians and archaeologists have neglected the role of bridges.”
Dr. Ochsendorf’s research on Inca suspension bridges, begun while he was an undergraduate at Cornell University, illustrates an engineering university’s approach to archaeology, combining materials science and experimentation with the traditional fieldwork of observing and dating artifacts. Other universities conduct research in archaeological materials, but it has long been a specialty at M.I.T.
Students here are introduced to the multidisciplinary investigation of ancient technologies as applied in transforming resources into cultural hallmarks from household pottery to grand pyramids. In a course called “materials in human experience,” students are making a 60-foot-long fiber bridge in the Peruvian style. On Saturday, they plan to stretch the bridge across a dry basin between two campus buildings.
In recent years, M.I.T. archaeologists and scientists have joined forces in studies of early Peruvian ceramics, balsa rafts and metal alloys; Egyptian glass and Roman concrete; and also the casting of bronze bells in Mexico. They discovered that Ecuadoreans, traveling by sea, introduced metallurgy to western Mexico. They even found how Mexicans added bits of morning-glory plants, which contain sulfur, in processing natural rubber into bouncing balls.
“Mexicans discovered vulcanization 3,500 years before Goodyear,” said Dorothy Hosler, an M.I.T. professor of archaeology and ancient technology. “The Spanish had never seen anything that bounced like the rubber balls of Mexico.”
Heather Lechtman, an archaeologist of ancient technology who helped develop the M.I.T. program, said that in learning “how objects were made, what they were made of and how they were used, we see people making decisions at various stages, and the choices involve engineering as well as culture.”
From this perspective, she said, the choices are not always based only on what works well, but also are guided by ideological and aesthetic criteria. In the casting of early Mexican bells, attention was given to their ringing tone and their color; an unusually large amount of arsenic was added to copper to make the bronze shine like silver.
“If people use materials in different ways in different societies, that tells you something about those people,” Professor Lechtman said.
In the case of the Peruvian bridges, the builders relied on a technology well suited to the problem and their resources. The Spanish themselves demonstrated how appropriate the Peruvian technique was.
Dr. Ochsendorf, a specialist in early architecture and engineering, said the colonial government tried many times to erect European arch bridges across the canyons, and each attempt ended in fiasco until iron and steel were applied to bridge building. The Peruvians, knowing nothing of the arch or iron metallurgy, instead relied on what they knew best, fibers from cotton, grasses and saplings, and llama and alpaca wool.
The Inca suspension bridges achieved clear spans of at least 150 feet, probably much greater. This was a longer span than any European masonry bridges at the time. The longest Roman bridge in Spain had a maximum span between supports of 95 feet. And none of these European bridges had to stretch across deep canyons.
The Peruvians apparently invented their fiber bridges independently of outside influences, Dr. Ochsendorf said, but these bridges were neither the first of their kind in the world nor the inspiration for the modern suspension bridge like the George Washington and Verrazano-Narrows Bridges in New York and the Golden Gate in San Francisco.
In a recent research paper, Dr. Ochsendorf wrote: “The Inca were the only ancient American civilization to develop suspension bridges. Similar bridges existed in other mountainous regions of the world, most notably in the Himalayas and in ancient China, where iron chain suspension bridges existed in the third century B.C.”
The first of the modern versions was erected in Britain in the late 18th century, the beginning of the Industrial Revolution. The longest one today connects two islands in Japan, with a span of more than 6,000 feet from tower to supporting tower. These bridges are really “hanging roadways,” Dr. Ochsendorf said, to provide a fairly level surface for wheeled traffic.
In his authoritative 1984 book, “The Inka Road System,” John Hyslop, who was an official of the Institute of Andean Research and associated with the American Museum of Natural History, compiled descriptions of the Inca bridges recorded by early travelers.
Garcilasco de la Vega, in 1604, reported on the cable-making techniques. The fibers, he wrote, were braided into ropes of the length necessary for the bridge. Three of these ropes were woven together to make a larger rope, and three of them were again braided to make a still larger rope, and so on. The thick cables were pulled across the river with small ropes and attached to stone abutments on each side.
Three of the big cables served as the floor of the bridge, which often was at least four to five feet wide, and two others served as handrails. Pieces of wood were tied to the cable floor. Finally, the floor was strewn with branches to give firm footing for beasts of burden.
More branches and pieces of wood were strung to make walls along the entire length of the bridge. The side covering, one chronicler said, was such that “if a horse fell on all fours, it could not fall off the bridge.”
Still, it took a while for the Spanish to adjust to the bridges and to coax their horses to cross them. The bridges trembled underfoot and swayed dangerously in stiff winds.
Ephraim G. Squier, a visitor to Peru from the United States in the 1870s, said of the Apurimac River bridge: “It is usual for the traveler to time his day’s journey so as to reach the bridge in the morning, before the strong wind sets in; for, during the greater part of the day, it sweeps up the Canyon of the Apurimac with great force, and then the bridge sways like a gigantic hammock, and crossing is next to impossible.”
Other travelers noted that in many cases, two suspension bridges stood side by side. Some said that one was for the lords and gentry, the other for commoners; or one for men, the other for women.
Recent scholars have suggested that it was more likely that one bridge served as a backup for the other, considering the need for frequent repairs of frayed and worn ropes.
The last existing Inca suspension bridge, at Huinchiri, near Cuzco, is virtually rebuilt each year. People from the villages on either side hold a three-day festival and gather stiff grasses for producing more than 50,000 feet of cord. Finally, the cord is braided into 150-foot replacement cables.
In the M.I.T. class project, 14 students met two evenings a week and occasional afternoons to braid the ropes for a Peruvian bridge replica 60 feet long and 2 feet wide. They were allowed one important shortcut: some 50 miles of twine already prepared from sisal, a stronger fiber than the materials used by the Inca.
Some of the time thus gained was invested in steps the Inca had never thought of. The twine and the completed ropes were submitted to stress tests, load-bearing measurements and X-rays.
“We have proof-tested the stuff at every step as we go along,” said Linn W. Hobbs, a materials science professor and one of the principal teachers of the course.
The students incorporated 12 strands of twine for each primary rope. Then three of these 12-ply ropes were braided into the major cables, each 120 feet long — 60 feet for the span and 30 feet at each end for tying the bridge to concrete anchors.
One afternoon last week, several of the students stretched ropes down a long corridor, braiding one of the main cables. While one student knelt to make the braid and three students down the line did some nimble footwork to keep the separate ropes from entangling, Zack Jackowski, a sophomore, put a foot firmly down on the just-completed braid.
“It’s important to get the braids as tight as possible,” Mr. Jackowski said. “A little twist, pull it back hard, hold the twist you just put in.”
No doubt the students will escape the fate of Brother Juniper, the Franciscan missionary in Wilder’s novel who investigated the five people who perished in the collapse of the bridge of San Luis Rey.
Brother Juniper hoped to discern scientific evidence of divine intervention in human affairs, examples of “the wicked visited by destruction and the good called early to Heaven.”
Alas, he could not; there is some of both good and evil in people. So his written account was judged heretical. He and his manuscript were burned at the stake.
If the students’ bridge holds, they will have learned one lesson: engineering, in antiquity as now, is the process of finding a way through and over the challenges of environment and culture.
Jury Is Still Out on Gluten, the Latest Dietary Villain
By KATE MURPHY, The New York Times, May 8, 2007
Brandi Walzer, a 29-year-old cartographer in Savannah, Ga., loves bread, not to mention pizza and beer. But she tries to avoid them, because they contain gluten — a substance she says upsets her stomach, aggravates her arthritis and touches off depression.
She is among a growing number of Americans who believe that gluten — a protein found in wheat, barley and rye — is responsible for a variety of ills, from skin eruptions to infertility to anxiety to gas. Though diagnostic tests have not indicated she has an allergy or sensitivity to gluten, she nonetheless says she is better off without it.
“I struggle with sticking to a gluten-free diet,” she said, “but when I do, I feel much better.”
There is no question that eating gluten aggravates celiac disease, an autoimmune disorder that damages the small intestine and interferes with absorption of nutrients. But doctors say it is unclear whether gluten can be blamed for other problems.
Nevertheless, it has become a popular dietary villain. Gluten-free foods are popping up on grocery-store shelves and restaurant menus, including those of national chains like P. F. Chang’s and Outback Steakhouse. Warnings of gluten’s evils are common on alternative medicine Web sites and message boards.
“A lot of alternative practitioners like chiropractors have picked up on it and are waving around magic silver balls, crystals and such, telling people they have gluten intolerance,” said Dr. Don W. Powell, a gastroenterologist at the University of Texas Medical Branch at Galveston.
Sloane Miller, a 35-year-old freelance editor in New York, went on a gluten-free diet six months ago on the advice of her acupuncturist, even though a blood test and a biopsy indicated that she did not have celiac disease. Long plagued with gastrointestinal distress and believing that she might have an undetectable sensitivity to gluten, Ms. Miller said giving it up was “worth a try.”
Dr. Joseph A. Murray, a gastroenterologist at the Mayo Clinic in Rochester, Minn., who specializes in diagnosing and treating celiac disease, says such advice may be misguided. “There’s this ‘go blame gluten’ thing going on,” he said. “It’s difficult to sort out science from the belief.”
To be sure, whole wheat and other cereal grains that contain gluten can be hard to digest. The bran and germ components tend to pass through the alimentary canal intact, which is why they are often prescribed as a sort of natural broom to relieve constipation — and why they can also cause gas and diarrhea.
Processed and refined wheat products can cause a spike in blood sugar, followed by a drop, that can also make people feel ill. “If you stop eating the beloved Twinkie or fast foods because they contain wheat, then sure you’re going to feel better,” Dr. Murray said. Indeed, many people go on a gluten-free diet not to cure some ill but to lose weight by cutting down on carbohydrates.
Gluten is relatively new to the human diet, as wheat cultivation began only some 10,000 years ago. Now it is ubiquitous, not only in processed foods (including salad dressings, ice cream and peanut butter) but even in the adhesives on envelopes as well as in lipsticks and lotions. “It’s very hard to get away from gluten,” said Dr. Powell of the University of Texas.
Gluten is also making headlines now, because some Chinese suppliers are accused of slipping the industrial chemical melamine into wheat gluten that was added to American pet food, resulting in a product recall. But there is no indication that the contaminated gluten got into the human food supply.
While gluten allergies that provoke an immune response like hives or respiratory problems are rare, celiac disease is more common than once thought. The prevalence in North America was previously estimated at about 1 in 3,000, but several studies published in the last three years indicate that it is closer to 1 in 100 — and 1 in 22 for those with risk factors like having an immediate relative with celiac disease.
Though no one knows for sure, the revised numbers can probably be attributed to increasing incidence as well as better screening tools. “Chances are now that people actually know someone who has it,” said Dr. Peter H. R. Green, director of the Celiac Disease Center at Columbia University College of Physicians and Surgeons.
With increased awareness, he said, more people have begun to suspect that they have celiac disease or some milder form of gluten intolerance and decide to eliminate wheat, barley and rye from their diet without proper diagnosis. Ms. Walzer, for example, gave up gluten a year and half ago upon learning she had symptoms similar to those of a co-worker with celiac disease.
Though no test for celiac disease is definitive, the most powerful indicator is a blood test widely used for three years that measures levels of antitissue transglutaminase, or anti-tTG, the antibodies to an enzyme the body secretes when gluten irritates or damages the small intestine.
People with celiac disease have high levels of anti-tTG, suggesting that the body is attacking its own secretions. This autoimmune response leads to destruction of the lining of the small intestine and consequent malabsorption of nutrients. (The test will not be accurate if someone has already stopped eating gluten.) The blood test is usually followed by a duodenal biopsy before a diagnosis of celiac disease is made. The final proof is reversal of symptoms on a gluten-free diet.
Earlier blood tests and a DNA test were far less predictive, and celiac disease has been difficult to identify, especially because its symptoms vary widely. Ann Austin McCormick, a 64-year-old retired elementary school principal in Crosslake, Minn., said she had chronic diarrhea and anemia before she got a diagnosis of celiac disease five years ago. Colin Leslie, a 15-year-old high school student in Rye, N.Y., said he suffered from severe joint pain and headaches before receiving a diagnosis in 2005.
Still others have no symptoms at all — merely a latent form of the disease that may become apparent only after a stressful physiological or psychological event like a serious illness or death of a spouse.
Researchers in the United States, Italy and Great Britain have hypothesized that the incidence of celiac disease is on the rise worldwide because wheat has become so prevalent in the Western diet that humans are actually overdosing on it. While debatable, this view could also account for cases like those of Ms. Walzer and Ms. Miller, who believe they have subclinical gluten sensitivity.
Currently, the only treatment for celiac disease or a more subjective gluten sensitivity is to avoid eating anything containing gluten. Sensing an opportunity, several companies, including Alba Therapeutics and Alvine Pharmaceuticals Inc., are working to find drugs to inhibit the destructive autoimmune response to gluten that is characteristic of celiac disease.
And dietary supplement makers are in a race to develop enzyme formulations that will help people digest gluten, just as lactase pills and drops were developed in the 1980s to help people digest lactose in dairy products.
But with supermarkets brimming with gluten-free breads, cereals, cakes and cookies and restaurants serving gluten-free pastas, pizzas and beer, it has become far less difficult to stay on a gluten-free diet.
“It’s easy to go gluten-free,” Ms. Miller said. “I don’t miss it at all.”
From DNA Analysis, Clues to a Single Australian Migration
By NICHOLAS WADE, The New York Times, May 8, 2007
Geneticists re-examining the first settlement of Australia and Papua-New Guinea by modern humans have concluded that the two islands were reached some 50,000 years ago by a single group of people who remained in substantial or total isolation until recent times. The finding, if upheld, would undermine assumptions that there have been subsequent waves of migration into Australia.
Analyzing old and new samples of Aborigine DNA, which are hard to obtain because of governmental restrictions, the geneticists developed a detailed picture of the aborigines’ ancestry, as reflected in their Y chromosomes, found just in men, and their mitochondrial DNA, a genetic element passed down just through the mother.
The results show that Aborigines and the people of Papua-New Guinea share several ancient genetic lineages, indicating that both are descended from a single founding population.
All Australian Aborigines, at least to judge by the genetic samples in hand, are descended from this founding population, meaning that no further immigrants reached Australia in numbers large enough to leave a genetic trace until the modern era.
The findings, by Toomas Kisivild and a group of geneticists and archaeologists situated mostly at the University of Cambridge in England, are reported today in The Proceedings of the National Academy of Sciences.
The oldest human remains from Australia, about 45,000 years in age, have quite thin or gracile bones, whereas fossils from 20,000 years ago are robust. The new findings suggest that the difference must stem from some internal process like adaptation to climatic change, and not to interbreeding with the archaic species Homo erectus, as some have suggested.
The new genetic analysis also undercuts the theory that the dingo, a dog that appeared in Australia 4,000 years ago, arrived with a new wave of settlers. Dr. Kisivild suggested that the dingo could have been an item of trade. But Richard G. Klein, a paleoanthropologist at Stanford University, said new immigrants were more likely to have introduced the dog, even though they were too few to have left a genetic trace.
Dr. Kisivild’s team has also been able to estimate, by counting mutations in DNA, the duration of the emigrants’ journey from India, an early point of settlement outside Africa, to the lost continent of Sahul that then included New Guinea and Australia.
The journey would have taken less than 5,200 years, the geneticists calculate, as a growing population gradually spread along the coastlines of southeastern Asia. The emigrants would have had to cross open sea only at the final stage of their journey.
The genetic estimates for the duration of the journey are “intriguing, but not compelling,” Dr. Klein said. “I think we need lots more archaeological evidence to resolve the question of how long it took modern humans to spread from Africa to Australia or anywhere else.”
The oldest inhabitants of New Guinea, who speak languages of the Papuan family, would have changed under the evolutionary forces of selection and genetic drift. Still, modern Papuan speakers may offer “a pretty good idea of what our ancestors might have looked like coming out of Africa 2,000 generations ago,” said Peter Forster of Anglia Ruskin University in Cambridge, an author of the new report.
Dr. Klein, however, said that aboriginal Australians and Papuans differed in appearance from that expected for the earliest fossil remains in Australia and that their morphology had to have emerged later.
“I don’t think genetics implies that aboriginal Australians and Papuans resemble the original modern African emigrants more closely than anyone else,” he said.
Vital Signs: Adolescence: No Link to Promiscuity Found in Youths Using Condoms
By NICHOLAS BAKALAR, The New York Times, May 8, 2007
A new study has found that adolescents who use condoms the first time they have intercourse do not go on to have more sexual partners than others, and that they have lower rates of sexually transmitted diseases than those who do not use condoms the first time.
Beginning in 1994, the researchers studied a sample of 4,018 teenagers, all of whom completed three interviews about their sexual behavior over a period of six to eight years. All had had sexual intercourse by the second year of the study. Participants were tested for chlamydia and gonorrhea in 2001 or 2002.
Almost 62 percent of the teenagers used a condom the first time they had sex. Despite concerns that encouraging condom use leads to promiscuity, those who used condoms and those who did not had an average of five partners. But those who used a condom at their sexual debut were only half as likely to have a sexually transmitted disease seven years later.
The authors acknowledge that some of their data depend on self-reporting, which can be unreliable, and that many questionnaire items were retrospective, which can lead to errors in recall.
Still, said Dr. Taraneh Shafii, the lead author, “in determining what are healthy sexual habits, we have to look to research to see what the evidence shows. Our evidence shows that youth who use condoms the first time they have sex are less likely to test positive for gonorrhea or chlamydia seven years later.” Dr. Shafii is an assistant professor of pediatrics at the University of Washington.
The study will appear in the June issue of The American Journal of Public Health.
By JOHN NOBLE WILFORD, The New York Times, May 8, 2007
CAMBRIDGE, Mass. — Conquistadors from Spain came, they saw and they were astonished. They had never seen anything in Europe like the bridges of Peru. Chroniclers wrote that the Spanish soldiers stood in awe and fear before the spans of braided fiber cables suspended across deep gorges in the Andes, narrow walkways sagging and swaying and looking so frail.
Yet the suspension bridges were familiar and vital links in the vast empire of the Inca, as they had been to Andean cultures for hundreds of years before the arrival of the Spanish in 1532. The people had not developed the stone arch or wheeled vehicles, but they were accomplished in the use of natural fibers for textiles, boats, sling weapons — even keeping inventories by a prewriting system of knots.
So bridges made of fiber ropes, some as thick as a man’s torso, were the technological solution to the problem of road building in rugged terrain. By some estimates, at least 200 such suspension bridges spanned river gorges in the 16th century. One of the last of these, over the Apurimac River, inspired Thornton Wilder’s novel “The Bridge of San Luis Rey.”
Although scholars have studied the Inca road system’s importance in forging and controlling the pre-Columbian empire, John A.Ochsendorf of the Massachusetts Institute of Technology here said, “Historians and archaeologists have neglected the role of bridges.”
Dr. Ochsendorf’s research on Inca suspension bridges, begun while he was an undergraduate at Cornell University, illustrates an engineering university’s approach to archaeology, combining materials science and experimentation with the traditional fieldwork of observing and dating artifacts. Other universities conduct research in archaeological materials, but it has long been a specialty at M.I.T.
Students here are introduced to the multidisciplinary investigation of ancient technologies as applied in transforming resources into cultural hallmarks from household pottery to grand pyramids. In a course called “materials in human experience,” students are making a 60-foot-long fiber bridge in the Peruvian style. On Saturday, they plan to stretch the bridge across a dry basin between two campus buildings.
In recent years, M.I.T. archaeologists and scientists have joined forces in studies of early Peruvian ceramics, balsa rafts and metal alloys; Egyptian glass and Roman concrete; and also the casting of bronze bells in Mexico. They discovered that Ecuadoreans, traveling by sea, introduced metallurgy to western Mexico. They even found how Mexicans added bits of morning-glory plants, which contain sulfur, in processing natural rubber into bouncing balls.
“Mexicans discovered vulcanization 3,500 years before Goodyear,” said Dorothy Hosler, an M.I.T. professor of archaeology and ancient technology. “The Spanish had never seen anything that bounced like the rubber balls of Mexico.”
Heather Lechtman, an archaeologist of ancient technology who helped develop the M.I.T. program, said that in learning “how objects were made, what they were made of and how they were used, we see people making decisions at various stages, and the choices involve engineering as well as culture.”
From this perspective, she said, the choices are not always based only on what works well, but also are guided by ideological and aesthetic criteria. In the casting of early Mexican bells, attention was given to their ringing tone and their color; an unusually large amount of arsenic was added to copper to make the bronze shine like silver.
“If people use materials in different ways in different societies, that tells you something about those people,” Professor Lechtman said.
In the case of the Peruvian bridges, the builders relied on a technology well suited to the problem and their resources. The Spanish themselves demonstrated how appropriate the Peruvian technique was.
Dr. Ochsendorf, a specialist in early architecture and engineering, said the colonial government tried many times to erect European arch bridges across the canyons, and each attempt ended in fiasco until iron and steel were applied to bridge building. The Peruvians, knowing nothing of the arch or iron metallurgy, instead relied on what they knew best, fibers from cotton, grasses and saplings, and llama and alpaca wool.
The Inca suspension bridges achieved clear spans of at least 150 feet, probably much greater. This was a longer span than any European masonry bridges at the time. The longest Roman bridge in Spain had a maximum span between supports of 95 feet. And none of these European bridges had to stretch across deep canyons.
The Peruvians apparently invented their fiber bridges independently of outside influences, Dr. Ochsendorf said, but these bridges were neither the first of their kind in the world nor the inspiration for the modern suspension bridge like the George Washington and Verrazano-Narrows Bridges in New York and the Golden Gate in San Francisco.
In a recent research paper, Dr. Ochsendorf wrote: “The Inca were the only ancient American civilization to develop suspension bridges. Similar bridges existed in other mountainous regions of the world, most notably in the Himalayas and in ancient China, where iron chain suspension bridges existed in the third century B.C.”
The first of the modern versions was erected in Britain in the late 18th century, the beginning of the Industrial Revolution. The longest one today connects two islands in Japan, with a span of more than 6,000 feet from tower to supporting tower. These bridges are really “hanging roadways,” Dr. Ochsendorf said, to provide a fairly level surface for wheeled traffic.
In his authoritative 1984 book, “The Inka Road System,” John Hyslop, who was an official of the Institute of Andean Research and associated with the American Museum of Natural History, compiled descriptions of the Inca bridges recorded by early travelers.
Garcilasco de la Vega, in 1604, reported on the cable-making techniques. The fibers, he wrote, were braided into ropes of the length necessary for the bridge. Three of these ropes were woven together to make a larger rope, and three of them were again braided to make a still larger rope, and so on. The thick cables were pulled across the river with small ropes and attached to stone abutments on each side.
Three of the big cables served as the floor of the bridge, which often was at least four to five feet wide, and two others served as handrails. Pieces of wood were tied to the cable floor. Finally, the floor was strewn with branches to give firm footing for beasts of burden.
More branches and pieces of wood were strung to make walls along the entire length of the bridge. The side covering, one chronicler said, was such that “if a horse fell on all fours, it could not fall off the bridge.”
Still, it took a while for the Spanish to adjust to the bridges and to coax their horses to cross them. The bridges trembled underfoot and swayed dangerously in stiff winds.
Ephraim G. Squier, a visitor to Peru from the United States in the 1870s, said of the Apurimac River bridge: “It is usual for the traveler to time his day’s journey so as to reach the bridge in the morning, before the strong wind sets in; for, during the greater part of the day, it sweeps up the Canyon of the Apurimac with great force, and then the bridge sways like a gigantic hammock, and crossing is next to impossible.”
Other travelers noted that in many cases, two suspension bridges stood side by side. Some said that one was for the lords and gentry, the other for commoners; or one for men, the other for women.
Recent scholars have suggested that it was more likely that one bridge served as a backup for the other, considering the need for frequent repairs of frayed and worn ropes.
The last existing Inca suspension bridge, at Huinchiri, near Cuzco, is virtually rebuilt each year. People from the villages on either side hold a three-day festival and gather stiff grasses for producing more than 50,000 feet of cord. Finally, the cord is braided into 150-foot replacement cables.
In the M.I.T. class project, 14 students met two evenings a week and occasional afternoons to braid the ropes for a Peruvian bridge replica 60 feet long and 2 feet wide. They were allowed one important shortcut: some 50 miles of twine already prepared from sisal, a stronger fiber than the materials used by the Inca.
Some of the time thus gained was invested in steps the Inca had never thought of. The twine and the completed ropes were submitted to stress tests, load-bearing measurements and X-rays.
“We have proof-tested the stuff at every step as we go along,” said Linn W. Hobbs, a materials science professor and one of the principal teachers of the course.
The students incorporated 12 strands of twine for each primary rope. Then three of these 12-ply ropes were braided into the major cables, each 120 feet long — 60 feet for the span and 30 feet at each end for tying the bridge to concrete anchors.
One afternoon last week, several of the students stretched ropes down a long corridor, braiding one of the main cables. While one student knelt to make the braid and three students down the line did some nimble footwork to keep the separate ropes from entangling, Zack Jackowski, a sophomore, put a foot firmly down on the just-completed braid.
“It’s important to get the braids as tight as possible,” Mr. Jackowski said. “A little twist, pull it back hard, hold the twist you just put in.”
No doubt the students will escape the fate of Brother Juniper, the Franciscan missionary in Wilder’s novel who investigated the five people who perished in the collapse of the bridge of San Luis Rey.
Brother Juniper hoped to discern scientific evidence of divine intervention in human affairs, examples of “the wicked visited by destruction and the good called early to Heaven.”
Alas, he could not; there is some of both good and evil in people. So his written account was judged heretical. He and his manuscript were burned at the stake.
If the students’ bridge holds, they will have learned one lesson: engineering, in antiquity as now, is the process of finding a way through and over the challenges of environment and culture.
Jury Is Still Out on Gluten, the Latest Dietary Villain
By KATE MURPHY, The New York Times, May 8, 2007
Brandi Walzer, a 29-year-old cartographer in Savannah, Ga., loves bread, not to mention pizza and beer. But she tries to avoid them, because they contain gluten — a substance she says upsets her stomach, aggravates her arthritis and touches off depression.
She is among a growing number of Americans who believe that gluten — a protein found in wheat, barley and rye — is responsible for a variety of ills, from skin eruptions to infertility to anxiety to gas. Though diagnostic tests have not indicated she has an allergy or sensitivity to gluten, she nonetheless says she is better off without it.
“I struggle with sticking to a gluten-free diet,” she said, “but when I do, I feel much better.”
There is no question that eating gluten aggravates celiac disease, an autoimmune disorder that damages the small intestine and interferes with absorption of nutrients. But doctors say it is unclear whether gluten can be blamed for other problems.
Nevertheless, it has become a popular dietary villain. Gluten-free foods are popping up on grocery-store shelves and restaurant menus, including those of national chains like P. F. Chang’s and Outback Steakhouse. Warnings of gluten’s evils are common on alternative medicine Web sites and message boards.
“A lot of alternative practitioners like chiropractors have picked up on it and are waving around magic silver balls, crystals and such, telling people they have gluten intolerance,” said Dr. Don W. Powell, a gastroenterologist at the University of Texas Medical Branch at Galveston.
Sloane Miller, a 35-year-old freelance editor in New York, went on a gluten-free diet six months ago on the advice of her acupuncturist, even though a blood test and a biopsy indicated that she did not have celiac disease. Long plagued with gastrointestinal distress and believing that she might have an undetectable sensitivity to gluten, Ms. Miller said giving it up was “worth a try.”
Dr. Joseph A. Murray, a gastroenterologist at the Mayo Clinic in Rochester, Minn., who specializes in diagnosing and treating celiac disease, says such advice may be misguided. “There’s this ‘go blame gluten’ thing going on,” he said. “It’s difficult to sort out science from the belief.”
To be sure, whole wheat and other cereal grains that contain gluten can be hard to digest. The bran and germ components tend to pass through the alimentary canal intact, which is why they are often prescribed as a sort of natural broom to relieve constipation — and why they can also cause gas and diarrhea.
Processed and refined wheat products can cause a spike in blood sugar, followed by a drop, that can also make people feel ill. “If you stop eating the beloved Twinkie or fast foods because they contain wheat, then sure you’re going to feel better,” Dr. Murray said. Indeed, many people go on a gluten-free diet not to cure some ill but to lose weight by cutting down on carbohydrates.
Gluten is relatively new to the human diet, as wheat cultivation began only some 10,000 years ago. Now it is ubiquitous, not only in processed foods (including salad dressings, ice cream and peanut butter) but even in the adhesives on envelopes as well as in lipsticks and lotions. “It’s very hard to get away from gluten,” said Dr. Powell of the University of Texas.
Gluten is also making headlines now, because some Chinese suppliers are accused of slipping the industrial chemical melamine into wheat gluten that was added to American pet food, resulting in a product recall. But there is no indication that the contaminated gluten got into the human food supply.
While gluten allergies that provoke an immune response like hives or respiratory problems are rare, celiac disease is more common than once thought. The prevalence in North America was previously estimated at about 1 in 3,000, but several studies published in the last three years indicate that it is closer to 1 in 100 — and 1 in 22 for those with risk factors like having an immediate relative with celiac disease.
Though no one knows for sure, the revised numbers can probably be attributed to increasing incidence as well as better screening tools. “Chances are now that people actually know someone who has it,” said Dr. Peter H. R. Green, director of the Celiac Disease Center at Columbia University College of Physicians and Surgeons.
With increased awareness, he said, more people have begun to suspect that they have celiac disease or some milder form of gluten intolerance and decide to eliminate wheat, barley and rye from their diet without proper diagnosis. Ms. Walzer, for example, gave up gluten a year and half ago upon learning she had symptoms similar to those of a co-worker with celiac disease.
Though no test for celiac disease is definitive, the most powerful indicator is a blood test widely used for three years that measures levels of antitissue transglutaminase, or anti-tTG, the antibodies to an enzyme the body secretes when gluten irritates or damages the small intestine.
People with celiac disease have high levels of anti-tTG, suggesting that the body is attacking its own secretions. This autoimmune response leads to destruction of the lining of the small intestine and consequent malabsorption of nutrients. (The test will not be accurate if someone has already stopped eating gluten.) The blood test is usually followed by a duodenal biopsy before a diagnosis of celiac disease is made. The final proof is reversal of symptoms on a gluten-free diet.
Earlier blood tests and a DNA test were far less predictive, and celiac disease has been difficult to identify, especially because its symptoms vary widely. Ann Austin McCormick, a 64-year-old retired elementary school principal in Crosslake, Minn., said she had chronic diarrhea and anemia before she got a diagnosis of celiac disease five years ago. Colin Leslie, a 15-year-old high school student in Rye, N.Y., said he suffered from severe joint pain and headaches before receiving a diagnosis in 2005.
Still others have no symptoms at all — merely a latent form of the disease that may become apparent only after a stressful physiological or psychological event like a serious illness or death of a spouse.
Researchers in the United States, Italy and Great Britain have hypothesized that the incidence of celiac disease is on the rise worldwide because wheat has become so prevalent in the Western diet that humans are actually overdosing on it. While debatable, this view could also account for cases like those of Ms. Walzer and Ms. Miller, who believe they have subclinical gluten sensitivity.
Currently, the only treatment for celiac disease or a more subjective gluten sensitivity is to avoid eating anything containing gluten. Sensing an opportunity, several companies, including Alba Therapeutics and Alvine Pharmaceuticals Inc., are working to find drugs to inhibit the destructive autoimmune response to gluten that is characteristic of celiac disease.
And dietary supplement makers are in a race to develop enzyme formulations that will help people digest gluten, just as lactase pills and drops were developed in the 1980s to help people digest lactose in dairy products.
But with supermarkets brimming with gluten-free breads, cereals, cakes and cookies and restaurants serving gluten-free pastas, pizzas and beer, it has become far less difficult to stay on a gluten-free diet.
“It’s easy to go gluten-free,” Ms. Miller said. “I don’t miss it at all.”
From DNA Analysis, Clues to a Single Australian Migration
By NICHOLAS WADE, The New York Times, May 8, 2007
Geneticists re-examining the first settlement of Australia and Papua-New Guinea by modern humans have concluded that the two islands were reached some 50,000 years ago by a single group of people who remained in substantial or total isolation until recent times. The finding, if upheld, would undermine assumptions that there have been subsequent waves of migration into Australia.
Analyzing old and new samples of Aborigine DNA, which are hard to obtain because of governmental restrictions, the geneticists developed a detailed picture of the aborigines’ ancestry, as reflected in their Y chromosomes, found just in men, and their mitochondrial DNA, a genetic element passed down just through the mother.
The results show that Aborigines and the people of Papua-New Guinea share several ancient genetic lineages, indicating that both are descended from a single founding population.
All Australian Aborigines, at least to judge by the genetic samples in hand, are descended from this founding population, meaning that no further immigrants reached Australia in numbers large enough to leave a genetic trace until the modern era.
The findings, by Toomas Kisivild and a group of geneticists and archaeologists situated mostly at the University of Cambridge in England, are reported today in The Proceedings of the National Academy of Sciences.
The oldest human remains from Australia, about 45,000 years in age, have quite thin or gracile bones, whereas fossils from 20,000 years ago are robust. The new findings suggest that the difference must stem from some internal process like adaptation to climatic change, and not to interbreeding with the archaic species Homo erectus, as some have suggested.
The new genetic analysis also undercuts the theory that the dingo, a dog that appeared in Australia 4,000 years ago, arrived with a new wave of settlers. Dr. Kisivild suggested that the dingo could have been an item of trade. But Richard G. Klein, a paleoanthropologist at Stanford University, said new immigrants were more likely to have introduced the dog, even though they were too few to have left a genetic trace.
Dr. Kisivild’s team has also been able to estimate, by counting mutations in DNA, the duration of the emigrants’ journey from India, an early point of settlement outside Africa, to the lost continent of Sahul that then included New Guinea and Australia.
The journey would have taken less than 5,200 years, the geneticists calculate, as a growing population gradually spread along the coastlines of southeastern Asia. The emigrants would have had to cross open sea only at the final stage of their journey.
The genetic estimates for the duration of the journey are “intriguing, but not compelling,” Dr. Klein said. “I think we need lots more archaeological evidence to resolve the question of how long it took modern humans to spread from Africa to Australia or anywhere else.”
The oldest inhabitants of New Guinea, who speak languages of the Papuan family, would have changed under the evolutionary forces of selection and genetic drift. Still, modern Papuan speakers may offer “a pretty good idea of what our ancestors might have looked like coming out of Africa 2,000 generations ago,” said Peter Forster of Anglia Ruskin University in Cambridge, an author of the new report.
Dr. Klein, however, said that aboriginal Australians and Papuans differed in appearance from that expected for the earliest fossil remains in Australia and that their morphology had to have emerged later.
“I don’t think genetics implies that aboriginal Australians and Papuans resemble the original modern African emigrants more closely than anyone else,” he said.
Vital Signs: Adolescence: No Link to Promiscuity Found in Youths Using Condoms
By NICHOLAS BAKALAR, The New York Times, May 8, 2007
A new study has found that adolescents who use condoms the first time they have intercourse do not go on to have more sexual partners than others, and that they have lower rates of sexually transmitted diseases than those who do not use condoms the first time.
Beginning in 1994, the researchers studied a sample of 4,018 teenagers, all of whom completed three interviews about their sexual behavior over a period of six to eight years. All had had sexual intercourse by the second year of the study. Participants were tested for chlamydia and gonorrhea in 2001 or 2002.
Almost 62 percent of the teenagers used a condom the first time they had sex. Despite concerns that encouraging condom use leads to promiscuity, those who used condoms and those who did not had an average of five partners. But those who used a condom at their sexual debut were only half as likely to have a sexually transmitted disease seven years later.
The authors acknowledge that some of their data depend on self-reporting, which can be unreliable, and that many questionnaire items were retrospective, which can lead to errors in recall.
Still, said Dr. Taraneh Shafii, the lead author, “in determining what are healthy sexual habits, we have to look to research to see what the evidence shows. Our evidence shows that youth who use condoms the first time they have sex are less likely to test positive for gonorrhea or chlamydia seven years later.” Dr. Shafii is an assistant professor of pediatrics at the University of Washington.
The study will appear in the June issue of The American Journal of Public Health.
