by Dan Ariely
Lack believes that a child becomes tolerant of a variety of food proteins through exposure in the first six months of life. In developing countries, he notes, children often consume solids, initially chewed by their parents, at two or three months. “Years ago, nobody had blenders or food mixers, and today in developing countries people still don’t. The easiest way to get solid foods into a baby’s mouth is to chew it up, so it’s moist and coated with saliva, and then spit it into the baby’s mouth.”
A paper published in Maternal and Child Nutrition in January 2010 reported that some two-thirds of students at a university in China were given premasticated food as infants. Only about 14 percent of American infants receive solid foods in this way. Saliva is a rich source of enzymes that can help break down solid foods and of antibodies that might coat food proteins in a way that makes them less allergenic to infants.
Lack’s research has gradually gained influence with leading allergists, including Hugh Sampson. By 2006 Sampson realized that his recommendations about food avoidance did not conform to what he termed “the real world.” Doing nothing more than inhaling or touching an allergen could prompt a reaction in some children. “You can’t avoid food proteins,” Sampson said. “So when we put out these recommendations we allowed the infants to get intermittent and low-dose exposure, especially on the skin, which actually may have made them even more sensitive.”
Sampson believes that some 80 percent of infants who are allergic to eggs or milk will outgrow the allergy by their teenage years and that preventing them from being fed products with these foods may prolong the time that takes. “I spent most of my career telling mothers to avoid these types of foods for their babies,” he told me. “Now we’re testing to see if we should advise mothers to give the foods to them.”
In January 2008, the American Academy of Pediatrics released a clinical report by Mount Sinai’s Dr. Sicherer and other researchers that overturned the expert advice of the past decade: “Current evidence does not support a major role for maternal dietary restrictions during pregnancy or lactation. . . . There is also little evidence that delaying the timing of the introduction of complementary foods beyond four to six months of age prevents the occurrence of [allergies].” Dr. Frank Greer, a specialist in newborn nutrition at the University of Wisconsin School of Medicine and Public Health and an author of the clinical report, told me, “There is so much out there about how to feed infants, when to begin rice cereal, how to phase in yellow vegetables and then green vegetables, that has no basis in scientific evidence. It’s not surprising that recommendations were made which were based on so little data.”
Dr. Susan Baker, a professor of pediatrics at the State University of New York at Buffalo and an expert on nutrition for children, chaired the committee overseen by the AAP that released the recommendations in 2000. She told me that safety concerns drove the experts to recommend restricting exposure of infants to potentially allergenic foods, particularly cow’s milk. “At the time, there was a proliferation of infant formulas on the market. Babies not only have cow’s milk allergy with eczema, but some who are intolerant of milk also develop bloody diarrhea. The real concern was that the formulas might do harm. That sort of propelled us.” The committee, she said, moved from milk products to restricting other allergenic foods, like peanuts and fish. “We in medicine are making a lot of decisions and recommendations based on not a lot of solid evidence. So you toe a fine line. You want to try to get pediatricians something that is as good as it can be to help guide their practice and their thinking. Did we overreach with peanuts and other foods? Probably. Could it have been better? Absolutely.”
The 2000 recommendations have been overturned, but Gideon Lack is disturbed by what families now face. “Basically, we are all in limbo,” he said. Sicherer told me, “This is a tricky area. The AAP has backed away from making recommendations, since the evidence is weak. I try to emphasize with my patients not to feel guilty that they did or did not do something that would have resulted in their child having a food allergy. Even the experts are not certain what to advise.”
People with food allergies live under a constant threat in a society that is still poorly informed about the condition. For people with peanut and tree-nut allergies, incidents in restaurants account for nearly a quarter of unintentional exposures and about half of all fatal reactions.
In 2007 Sicherer published the results of a survey of a hundred managers, servers, and chefs in establishments ranging from continental restaurants to bakeries and delis. Focusing on New York City and Long Island, Sicherer found that about a quarter of managers and workers believed that consuming a small amount of the allergen would be safe; 35 percent believed that frying would destroy it; and a quarter thought it was safe to remove an allergen from a finished meal, like taking walnuts out of a salad. Nearly three-quarters of food workers believed that they knew how to “guarantee” a safe meal. Most states do not require that food providers attend educational programs, and there are no national requirements.
Sampson, acutely aware of the risks facing food-allergy sufferers, is now trying to work out a way to help desensitize people. To do this, he is relying on the idea behind the hygiene hypothesis and some of Lack’s investigations: that exposure in small doses, in controlled circumstances, can build tolerance. He is trying to identify how the IgE antibody attaches to different proteins, and he uses this knowledge to have foods cooked in a way that would make the proteins less allergenic. Researchers at Mount Sinai observed, for example, that baking caused milk proteins to change shape in a way that could be less provocative to the immune system. An allergic person might be able to eat the altered proteins and become tolerant of them in all their forms. Sampson and other researchers have also configured an experimental vaccine that contains fragments of peanut protein that might “reeducate” the immune system of allergic people. Safety studies of the experimental vaccine are under way at the Jaffe Institute.
In 2008, when Maya Konoff was seven, her mother enrolled her in a research study being conducted by Dr. Sampson at the Jaffe Food Allergy Institute, funded by the NIH. She was given allergens in an altered form, and if she achieved tolerance she would be given foods that contained the allergen in its more natural state.
The treatment rooms at the institute are painted in soft tones, and the hallways are decorated with large photographs of fruits. The institute has a spotless stainless-steel kitchen; all the refrigerators and cabinets are kept locked. Diego Baraona, the chef, prepares the foods. When I visited, he showed me a batch of small muffins he had baked, with applesauce and milk, and cups of rice pudding tightly sealed in plastic. With a nurse and Jill Mindlin at Maya’s side, the child was given a muffin. Maya tentatively took a bite, waited, and seemed to have no reaction. In short order, she ate the rest of the muffin. “It was very exciting for our family,” Mindlin recalled, “because it meant that she was one of those kids whose bodies didn’t recognize the milk protein when it was broken down in baking, so now she had potential to eat baked foods.”
The next step was to try a taste of pizza. Maya took her first bite, waited, smiled, and then took another two bites. “I knew right then that things were not going well, even though Maya had not exhibited any physical symptoms,” Mindlin said. “She had been so giddy, riding off the high of eating the muffin, happy and chattering, and then all of a sudden there was this pall that came over her.” Maya soon broke out in hives and began vomiting. Sampson gave her an epinephrine injection. As the drug took effect, the anaphylactic reaction was arrested.
According to the protocol, Maya was supposed to come back in six months. Dr. Sampson counseled that in the meantime she should eat baked foods that included milk. When she returned, an intravenous line was inserted and an epinephrine injection pen was placed at the bedside before Maya was offered a slice of the same pizza. “It was nothing less than miraculous,” her mother told me. “She ate the entire slice of pizza.” Maya was observed for several hours and then given a bowl
of rice pudding. The doctors told Mindlin to expect a reaction. “But instead she ate the whole bowl of rice pudding and was fine. She jumped two levels, just by eating muffins every day,” Mindlin said.
Maya returned to Mount Sinai the next day for a glass of milk. “That didn’t go quite as well,” Mindlin said. As Maya finished drinking, her nose began to run and she vomited. The allergic reaction was mild enough to be treated with Benadryl. When I spoke to Mindlin in December, she told me that Maya can now eat macaroni and cheese but that she is still unable to drink milk. “Even if she never progresses past this, I have no regrets about being in the study, because now she can go to a birthday party and have a slice of pizza. It’s huge.”
PART TWO: Animals
CARL ZIMMER
The Long, Curious, Extravagant Evolution of Feathers
FROM National Geographic
MOST OF US will never get to see nature’s greatest marvels in person. We won’t get a glimpse of a colossal squid’s eye, as big as a basketball. The closest we’ll get to a narwhal’s unicornlike tusk is a photograph. But there is one natural wonder that just about all of us can see, simply by stepping outside: dinosaurs using their feathers to fly.
Birds are so common, even in the most paved-over places on Earth, that it’s easy to take for granted both their dinosaur heritage and the ingenious plumage that keeps them aloft. To withstand the force of the oncoming air, a flight feather is shaped asymmetrically, the leading edge thin and stiff, the trailing edge long and flexible. To generate lift, a bird has merely to tilt its wings, adjusting the flow of air below and above them.
Airplane wings exploit some of the same aerodynamic tricks. But a bird wing is vastly more sophisticated than anything composed of sheet metal and rivets. From a central feather shaft extends a series of slender barbs, each sprouting smaller barbules, like branches from a bough, lined with tiny hooks. When these grasp the hooklets of neighboring barbules, they create a structural network that’s feather light but remarkably strong. When a bird preens its feathers to clean them, the barbs effortlessly separate, then slip back into place.
The origin of this wonderful mechanism is one of evolution’s most durable mysteries. In 1861, just two years after Darwin published Origin of Species, quarry workers in Germany unearthed spectacular fossils of a crow-size bird, dubbed Archaeopteryx, that lived about 150 million years ago. It had feathers and other traits of living birds but also vestiges of a reptilian past, such as teeth in its mouth, claws on its wings, and a long, bony tail. Like fossils of whales with legs, Archaeopteryx seemed to capture a moment in a critical evolutionary metamorphosis. “It is a grand case for me,” Darwin confided to a friend.
The case would have been even grander if paleontologists could have found a more ancient creature endowed with more primitive feathers—something they searched for in vain for most of the next century and a half. In the meantime, other scientists sought to illuminate the origin of feathers by examining the scales of modern reptiles, the closest living relatives of birds. Both scales and feathers are flat. So perhaps the scales of the birds’ ancestors had stretched out, generation after generation. Later their edges could have frayed and split, turning them into the first true feathers.
It made sense too that this change occurred as an adaptation for flight. Imagine the ancestors of birds as small, scaly, four-legged reptiles living in forest canopies, leaping from tree to tree. If their scales had grown longer, they would have provided more and more lift, allowing the protobirds to glide a little farther, then a little farther still. Only later might their arms have evolved into wings they could push up and down, transforming them from gliders to true powered fliers. In short, the evolution of feathers would have happened along with the evolution of flight.
This feathers-led-to-flight notion began to unravel in the 1970s, when the Yale University paleontologist John Ostrom noted striking similarities between the skeletons of birds and those of terrestrial dinosaurs called theropods, a group that includes marquee monsters like Tyrannosaurus rex and Velociraptor. Clearly, Ostrom argued, birds were the living descendants of theropods. Still, many known theropods had big legs, short arms, and stout, long tails—hardly the anatomy one would expect on a creature leaping from trees. Other paleontologists argued that birds did not evolve from dinosaurs—rather, their similarities derived from a shared common ancestor deeper in the past.
In 1996 Chinese paleontologists delivered startling support for Ostrom’s hypothesis. It was the fossil of a small, short-armed 125-million-year-old theropod, Sinosauropteryx, which had one extraordinary feature: a layer of thin, hollow filaments covering its back and tail. At last there was evidence of truly primitive feathers—found on a ground-running theropod. In short, the origin of feathers may have had nothing to do with the origin of flight.
Soon paleontologists were finding hundreds of feathered theropods. With so many fossils to compare, they began piecing together a more detailed history of the feather. First came simple filaments. Later, different lineages of theropods evolved various kinds of feathers, some resembling the fluffy down on birds today, some having symmetrically arranged barbs. Other theropods sported long, stiff ribbons or broad filaments, unlike the feathers on any living birds.
The long, hollow filaments on theropods posed a puzzle. If they were early feathers, how had they evolved from flat scales? Fortunately, there are theropods with threadlike feathers alive today: baby birds. All the feathers on a developing chick begin as bristles rising up from its skin; only later do they split open into more complex shapes. In the bird embryo these bristles erupt from tiny patches of skin cells called placodes. A ring of fast-growing cells on the top of the placode builds a cylindrical wall that becomes a bristle.
Reptiles have placodes too. But in a reptile embryo each placode switches on genes that cause only the skin cells on the back edge of the placode to grow, eventually forming scales. In the late 1990s Richard Prum of Yale University and Alan Brush of the University of Connecticut developed the idea that the transition from scales to feathers might have depended on a simple switch in the wiring of the genetic commands inside placodes, causing their cells to grow vertically through the skin rather than horizontally. In other words, feathers were not merely a variation on a theme: they were using the same genetic instruments to play a whole new kind of music. Once the first filaments had evolved, only minor modifications would have been required to produce increasingly elaborate feathers.
Until recently it was thought that feathers first appeared in an early member of the lineage of theropods that leads to birds. In 2009, however, Chinese scientists announced the discovery of a bristly-backed creature, Tianyulong, on the ornithischian branch of the dinosaur family tree—about as distant a relative of theropods as a dinosaur can be. This raised the astonishing possibility that the ancestor of all dinosaurs had hairlike feathers and that some species lost them later in evolution. The origin of feathers could be pushed back further still if the “fuzz” found on some pterosaurs is confirmed to be feathers, since these flying reptiles share an even older ancestor with dinosaurs.
There’s an even more astonishing possibility. The closest living relatives of birds, dinosaurs, and pterosaurs are crocodilians. Although these scaly beasts obviously do not have feathers today, the discovery of the same gene in alligators that is involved in building feathers in birds suggests that perhaps their ancestors did, 250 million years ago, before the lineages diverged. So perhaps the question to ask, say some scientists, is not how birds got their feathers, but how alligators lost theirs.
If feathers did not evolve first for flight, what other advantage could they have provided the creatures that had them? Some paleontologists have argued that feathers could have started out as insulation. Theropods have been found with their forelimbs spread over nests, and they may have been using feathers to shelter their young.
Another hypothesis has gained strength in recent years: that feathers first evolved to be seen. Feathers on bi
rds today come in a huge range of colors and patterns, with iridescent sheens and brilliant streaks and splashes. In some cases their beauty serves to attract the opposite sex. A peacock unfolds his iridescent train, for instance, to attract a peahen. The possibility that theropods evolved feathers for some kind of display got a big boost in 2009, when scientists began to take a closer look at their structure. They discovered microscopic sacs inside the feathers, called melanosomes, that correspond precisely in shape to structures associated with specific colors in the feathers of living birds. The melanosomes are so well preserved that scientists can actually reconstruct the color of dinosaur feathers. Sinosauropteryx’s tail, for example, appears to have had reddish and white stripes. Perhaps the males of the species flashed their handsome tails when courting females. Or perhaps both sexes used their stripes the way zebras use theirs—to recognize their own kind or confuse predators.
Whatever the original purpose of feathers, they were probably around for millions of years before a single lineage of dinosaurs began to use them for flight. Paleontologists are now carefully studying the closest theropod relatives of birds for clues to how this transition occurred. One of the most revealing is a recently discovered wonder called Anchiornis, more than 150 million years old. The size of a chicken, it had arm feathers with black-and-white portions, creating the spangled pattern you might see on a prize rooster at a county fair. On its head it wore a gaudy rufous crown. In structure, Anchiornis’s plumes were nearly identical to flight feathers, except that they were symmetrical rather than asymmetrical. Without a thin, stiff leading edge, they may have been too weak for flight.
