Feature Story: Genetically Modified Foods
In chapter seven of his environmental masterpiece Walden, Henry David Thoreau writes about his bean field: “…making the yellow soil express its summer thought in bean leaves and blossoms rather than in wormwood and piper and millet grass, making the earth say beans instead of grass—this was my daily work.”
You may wonder why I begin an essay on genetically modified foods with a quote from Thoreau. But to me, environmentalism and plant breeding are inextricably linked. Our civilization rests on our ability to make the earth say beans. Other creatures feed their young, but the adults of most species fend for themselves, spending much of their day doing it. By contrast, we humans have learned to farm. Over the last few centuries, advances in science have let fewer and fewer farmers feed more and more people, freeing the rest of us to make and sell each other hats and houses and computers, to be scientists and politicians, painters, teachers, doctors, spiritual leaders, and talk-show hosts. In some parts of the world, only one person in a hundred grows plants or raises animals for food. Most of us are surprisingly unaware of what it takes to create our bread and breakfast cereal, pasta and rice, those perfect fruits and vegetables, unblemished by insect bites or fungal spots. Free to live our lives with little thought for our food, we ignore the source of the gift.
Our civilization rests, in fact, on a history of tinkering with nature—on making the earth say beans instead of grass. Thoreau’s beans were not wild. The pod of a wild bean bursts when its seed is ripe, flinging the bean far from the parent plant to find a new place to sprout. The pods of those beans we grow for food do not burst. Such beans can no longer seed themselves. Nor can the wild grasses we have changed, over the millennia, into our staple food sources: rice, wheat, and corn. To change a wild plant into a food plant requires changes in the plant’s genes. To boost its yield, to make the earth say more beans, means changing the plant’s genes, as well. For thousands of years, farmers have been picking and choosing plants, propagating those with the genetic changes—mutations—that made them better food plants. Our civilization is the beneficiary of this genetic tinkering.
I have been studying plant genes—and tinkering with them—since the early 1980s, when I had the good fortune to work with Nobel Laureate Barbara McClintock, whose discovery of “transposons,” popularly called “jumping genes,” rewrote our concept of a gene. By identifying and cloning a jumping gene in 1984, I was able to identify the DNA sequences of McClintock’s transposons and then to analyze and understand how they operate. Today we know that the genome is full of transposable elements and is constantly changing. Instead of being static “beads on a string,” genes can move from one chromosome to another. Although the genes themselves are conserved over long evolutionary periods, there have been, and continue to be, numerous rearrangements, transpositions, duplications, and deletions, many of which are the work of the restless transposons.
McClintock and I worked on corn, and since then I and my students have used many of the techniques of genetic engineering invented in the last 20 years to uncover the secrets of how transposons and other kinds of plant genes work. I have never applied my knowledge to making a genetically modified crop, but my familiarity with both the techniques and the corn genome made me pay attention when corporations began doing so—and when the federal government began regulating the field-testing and marketing of these crops. I have given numerous public lectures on genetically modified foods and, with co-author Nancy Marie Brown , have written the book Mendel in the Kitchen: A Scientist’s View of Genetically Modified Foods , published in 2004 by Joseph Henry Press, an imprint of the National Academies Press.
For instance, when did people begin tinkering with the genes of plants? Corn—maize—is one of humankind’s greatest feats of genetic engineering. It looks nothing like a wild plant. Maize has no way of dispersing its seeds, stuck tight as they are on its enormous ears, which remain firmly attached to the plant. Scientists argued about what wild plant gave rise to maize for most of the 20th century. We now know its closest relative is a grass—teosinte. Discovered in 1896, teosinte looks so little like maize that it was assigned to a different genus: Teosinte was Euchleana mexicana; corn is Zea mays. Plants that belong to two different species (not to mention two different genera) are not supposed to cross-hybridize, but maize and teosinte do. Early genetic work by George Beadle (who would share the Nobel Prize in 1958 for the “one-gene one-enzyme” hypothesis) and his mentor Rollins Emerson of Cornell University suggested that a small number of genetic changes had transformed teosinte into maize, but it wasn’t until 1992 that John Doebley of the University of Wisconsin-Madison and his colleagues, using modern molecular techniques, concluded that no more than five major genetic regions—in some cases single genes—were responsible. Changes in one of the critical genes softened the hard, silica-containing surface of the seed; another created an ear-like structure with tightly adhering seeds; and yet another telescoped a side branch into the dense husk covering the contemporary corn plant’s ear.
To make corn, teosinte was genetically engineered by generations of farmers in the Balsas River basin of southern Mexico between 5,000 and 13,000 years ago. When scientists accepted teosinte as corn’s ancestor, late in the 20th century, they realized the two could not belong to different genera. So they renamed teosinte: It is now a subspecies, called parviglumis, of corn, Zea mays.
The teosinte plant, of course, had not changed at all—only our way of naming it. The classifications “genus” and “species” are not fixed and immutable. Nor does our current definition of species particularly apply to plants. Indica rice and Japonica rice, for example, are two popular types of cultivated rice, Oryza sativa. They are members of the same species, and it is often difficult to tell if a single grain comes from one type or the other. Yet they do not crossbreed.
Scientists in the 1950s, on the other hand, made a new, fertile grain called triticale by crossbreeding rye and durum wheat, which belong to two different genera. The secret to this early genetic engineering was colchicine, a chemical isolated from the autumn crocus. Colchicine doubles a plant’s chromosomes, making the normally sterile hybrid set seeds. By the mid-1980s, triticale was grown on more than two million acres worldwide; triticale flour is commonly found in health-food stores. Colchicine is also used to make fruits seedless. A favorite fruit produced this way is the seedless watermelon.
Another way to make seedless fruits is by using radiation to cause mutations. The Rio Red, a popular red grapefruit, was created by exposing grapefruit buds to thermal neutron radiation at Brookhaven National Laboratory in 1968. Other notable successes of mutation breeding include Creso, the most popular variety of durum wheat used for making pasta in Italy; Calrose 76, a high-yielding California rice; Golden Promise barley, a fine-quality malt used in specialty beers; and some 200 varieties of bread wheat grown around the world.
Such work is still going on. In 1996, citrus breeders Mikeal L. Roose and Tim Williams of the University of California, Riverside, irradiated budwood to develop a seedless clementine called Tango. (Generally, seedless clementines are made by spraying the flowers with a chemical that mimics a growth hormone.) By 2006, nurseries had orders for millions of Tango trees, and the researchers had extended their radiation-breeding program to include 63 varieties of citrus including mandarins, oranges, tangelos, lemons, and grapefruits.
In 2001, researchers at the Colorado and Texas Agricultural Experiment Stations even used radiation breeding to create a hard red winter wheat, called Above, that tolerates an herbicide produced by the BASF corporation. Above wheat can be sprayed with herbicide and will not die, letting farmers use energy-saving no-till techniques. Yet, although the end result is the same as the Roundup Ready crops sold by Monsanto, Above is not considered a “genetically modified organism” or GMO.
In fact, none of the many crop varieties created over the last 50 years through chemical or radiation mutation is considered a GMO, and they are not covered by the regulations that restrict the field-testing and sale of GM foods. In fact, they are not covered by any regulations at all, although many of the public’s concerns about GM crops—such as toxicity to humans or gene flow from modified crops to wild plants—apply to these crops as well.
GMO regulations only cover plant varieties created with molecular modification techniques, which plant breeders agree are more precise and controllable—and therefore safer—than the “conventional” techniques of chemical and radiation mutation.
The history of molecular-modification techniques begins in the late 1960s, when molecular biologists learned to isolate and study individual genes from among the tens of thousands of genes in every plant and animal. They began to decipher the information content of different organisms, from bacteria and yeast, plants and humans, discovering that genes change rather slowly. Maize plants and humans, for example, both have hemoglobin genes that code for rather similar oxygen-binding proteins, although they use them for very different purposes. Methods were developed as well to remove and replace genes and to add new ones. With a small amount of tweaking, any gene could work in almost any other organism. The functioning of genes and cells is so similar from one organism to another that if a bacterial gene is put into a plant, it will make the very same protein it did in the bacterium. Scientists also discovered that the movement of genes from one type of organism (such as a bacterium) to another (a plant) happens in nature. Building on that discovery, scientists developed ways to systematically introduce genes into plants in order to add just the right genes to help a plant withstand nature’s biological and physical stresses.
One of their first successes was in making plants disease-resistant. For example, Hawaii’s papaya plantations were saved from the scourge of the deadly papaya ringspot virus by expressing just a small genetic sequence of the virus in the plant. This sentinel gives the plants the ability to recognize and destroy an infecting virus before it can reproduce, much as we immunize children against the poliovirus, but by a different molecular mechanism. Other virus-resistant varieties include a plum that can withstand the plum pox virus that ravaged Pennsylvania recently, leading the state to invest $5.1 million towards its eradication. An heirloom variety of tomato, the San Marzano (said to be the inspiration for pizza), has been made resistant to the cucumber mosaic virus; by the year 2000, that virus had wiped out 90 percent of San Marzano production in its home fields near Naples, Italy. Unfortunately, neither the virus-resistant plum nor the tomato have been planted, due to anti-GMO activism. Widespread planting in Africa of a virus-resistant sweet potato, developed by Kenyan researcher Florence Wambugu through a collaboration with Monsanto, similarly has been delayed.
The most widely planted genetically modified crops are the corn and soybean varieties that tolerate herbicides, along with varieties of corn and cotton that produce an insecticidal protein from the bacterium Bacillus thuringiensis (Bt), long used by organic farmers to control insects. These crops, developed by a number of companies including Monsanto, Syngenta, and DuPont, have been found to substantially decrease farmers’ use of pesticides and herbicides. Moreover, because they protect corn plants from invasion by certain kinds of boring insects, the fungi that follow the insects do not infect the plants, substantially decreasing the contamination of the harvested corn by harmful mycotoxins.
“Today there is widespread acceptance in North and South America for the molecular modification of crop plants, and growing acceptance in China and India. Yet the status of crops modified by molecular techniques remains contentious in both Europe and Africa.” New crops under development are focusing on making foods healthier or easier to grow, especially in harsh environments. For instance, nitrogen fertilizer would no longer be necessary if corn, wheat, and rice could fix nitrogen from the air in the way that legumes, such as peas and beans, do. Nitrogen fixation is a complex symbiosis between the legume and rhizobial bacteria that live in nodules on the plant’s roots. In 2001, the DNA sequence of the rhizobial bacteria that fix nitrogen in alfalfa was published; since then more than 100 scientific studies have cited this article. A breakthrough announced by British workers in 2006 was inducing formation of the nodules without the presence of the bacteria.
In March 2007, researchers from the United States and China reported on how plants respond to the depletion of calcium from the soil, one effect of acid rain. This knowledge is a first step toward developing plant varieties that need less calcium. Other researchers are trying to make crops that are salt-tolerant, drought-tolerant, heat-tolerant, and cold-tolerant. Monsanto has identified genes that enable some plants to withstand drought and has created corn and soybean lines that grow with less water. Drought-tolerant corn is now undergoing field trials.
Researchers also are working on ways to make common foods healthier. Golden Rice, a rice that contains vitamin A, was created by Swiss researchers in 1999. The trait is currently being bred into varieties of rice traditionally grown in regions where vitamin A deficiency leads to high rates of blindness in children. In 2006, researchers in Florida reported they had bred a tomato that contains 20 times the normal amount of folate. A B vitamin, folate is needed to prevent anemia in pregnant women and birth defects in their children; lack of folate also increases the risk of vascular disease and cancer. A goal for future work is to fortify staple crops such as rice, sorghum, maize, or sweet potatoes with folate. Other researchers have made a temperate plant that produces a more-saturated, tropical-like oil which has baking properties like margarine without the transfats; a rice high in cancer-fighting flavonoids; potatoes with zeaxanthin, which wards off eye disease; and soybeans and canola oil that contain heart-healthy omega-3 fatty acids.
Oddly, these innovations aren’t called plant breeding, but “genetic engineering.” The new crops are not simply crops—as are the ones created using chemicals and radiation to modify plant genes—but genetically modified organisms.
GMOs have met with strong resistance. Before GMOs, people might have protested the use of synthetic fertilizers or pesticides in modern farming, but they were unconcerned about whatever it was that plant breeders had done to create high-yielding hybrid corn or brilliant red grapefruits or seedless watermelons. Now, however, many people seem to agree with Britain’s Prince Charles when he calls the new techniques of plant breeding “dangerous” and against God’s plan.
Part of the problem is in the words themselves. Much human effort goes into changing our environment, be it the building of highways, houses, air conditioners, shopping malls, dams, or airplanes. Although individual projects might meet with resistance, no one protests this kind of engineering. Yet the notion that plants were being engineered caught people by surprise. It was rather disquieting. Plants are, after all, natural, aren’t they? Might we not be messing with Mother Nature if we began to engineer plants?
The fantastic recent growth of electronic communication has amplified the ability to spread misinformation. Numerous organizations devote themselves to the active opposition of molecular approaches to plant breeding (though none, strangely, focus on radiation mutation, for example). Unfortunately, our understanding of scientific concepts, such as what a species is or what genes do, is often a vague mixture of fact and belief, leaving us ill-prepared to separate fact from fiction. What genetic engineering actually is and how it differs from earlier techniques of plant breeding is little known outside the laboratory and breeding plot. Our lack of knowledge could have tragic consequences. By stifling the creativity of plant breeders and by banning the results of their work from the marketplace, a “no-GMO” attitude could keep hungry people from being able to grow enough food.
Here is my concern as an environmentalist: The human population is too large, and the Earth too small, to sustain us in the ways our ancestors lived. Most of the land that is good for farming is already being farmed. Yet 80 million more humans are being added to the population each year. The challenge of the coming decades is to limit the destructive effects of agriculture even as we continue to coax more food from the earth. Simply to provide all people living today with the same amount of food available to each American, we need to increase crop yields—unless more land is to be brought into production, which means plowing up more wilderness.
We cannot turn the clock back. At the end of the Stone Age, when most people lived in small tribes hunting wild game and gathering wild plants, the world’s human population was stable at 8 to 10 million. When farming took hold as a way of life, the population began to grow. By the time of Christ, it had risen to between 100 and 300 million. When Columbus landed in the New World and the spread of food plants around the globe increased, the world’s population was about 450 million. In the late 1700s, when the science of chemistry entered agriculture, it had doubled to 900 million. A century later, when Gregor Mendel’s experiments were rediscovered, giving rise to the science of genetics, the population of the world was over one and a half billion.
In just the last hundred years the population doubled and redoubled. The number of people on Earth reached three billion in 1950, then jumped to six billion in little more than a single human generation. Yet farmers kept pace. Two important inventions early in the 20th century supported an enormous increase in farm productivity. First was the Haber-Bosch process for converting the gaseous nitrogen in the air to a form that plants can use as nitrogen fertilizer. Second was the observation of George Harrison Shull that intercrossing inbred corn varieties produces robust and productive offspring. This is the scientific underpinning of the entire hybrid corn industry.
These inventions initially benefited the developed world. By mid-century, doomsayers were predicting famines in India and China. These famines were averted by plant geneticists, who derived mutant strains of wheat, corn, and rice that were markedly more productive than indigenous strains. From the 1960s to the 1990s, the new crop varieties and expanding fertilizer use—the Green Revolution—continued to meet the world’s food needs. In 1950, 1.7 billion acres of farm land produced 692 million tons of grain. In 1992, with no real change in the number of acres under cultivation, the world’s farmers produced 1.9 billion tons of grain—a 170 percent increase. If India alone had rejected the high-yielding varieties of the Green Revolution, another 100 million acres of farm land—an area the size of California—would need to be plowed to produce the same amount of grain. That unfarmed land now protects the last of the tigers.
But the human population is still expanding. And there remain places in the world where malnutrition persists and hundreds of thousands of people, especially children, die for lack of food. Where will the next increments in food production come from? I believe they will come from genetic modification.
Today there is widespread acceptance in North and South America for the molecular modification of crop plants, and growing acceptance in China and India. In the first decade after these crops were introduced, their adoption progressed at a remarkable pace. By 2005, genetically modified crops, primarily cotton, corn and soybeans, were being grown by more than 8.5 million farmers in 21 different countries, with no substantiated reports of adverse health effects. Beneficial impacts, on the other hand, have been substantiated by peer-reviewed scientific studies, including the reduction in pesticide and herbicide use, the control of soil erosion through no-till farming, and the reduction in mycotoxin contamination of grain.
Yet the status of crops modified by molecular techniques remains contentious in both Europe and Africa. What remains to be seen is whether the wealth of the developed countries will be deployed to the benefit of the poorest countries, where people struggle to gain a foothold on the lowest rung of the economic ladder. Molecular modification of crop plants is expensive. And yet, as some of the examples I have given in this essay show, such modifications hold the promise of improving crop productivity under the most adverse climatic and biological conditions.
Nina V. Fedoroff