The pace of developing new varieties of plants and animals has quickened with the arrival of biotechnology. Biotechnology uses engineering techniques to modify organisms genetically for a particular purpose, ranging from producing varieties that provide a more dependable source of medicines to devising crops that are more nutritious. A genetically modified (GM) organism, or GMO, has one or more new genes introduced into its genetic makeup by biotechnology, using an array of engineering methods.

When the new genes come from other species, as is generally the case, GMOs are called transgenic organisms. For example, genes from the bacterium Bacillus thuringiensis have been inserted into the DNA of several crops, including corn, to increase the corn plant’s resistance to insects who chew on the plants.

In this process, a gene from B. thuringiensis, which codes for the insect-killing crystalline substance Bt, is inserted into the corn’s DNA. Because the transgenic, or GM, corn now carries this bacterial gene, it incorporates Bt crystals in its tissues as it grows. As a result, insects are poisoned when they feed on one of these GM corn varieties (Figure 7.28). Meanwhile, natural enemies of these pest insects, along with humans and other vertebrates, are seemingly unharmed by eating Bt-containing tissue, which is only toxic at the high pH levels that are found in the pest’s gut.

Most commercially grown GM crops have been engineered with three traits in mind: (1) the capacity to produce insect-killing chemicals (e.g., Bt), thereby increasing crop plants’ resistance to pests; (2) resistance to chemical herbicides, allowing farmers to control weeds with herbicides without harming crops; or (3) resistance to plant viruses, reducing losses of crop plants to these pathogens (Table 7.1).

210

The United States leads the world in the adoption of GM crops. For example, we grow more GM crops than in any other nation (see Table 7.1). Also, in 2010, farmers in the United States planted nearly 67 million hectares (165 million acres) in GM crops, dwarfing the plantings in other nations (Figure 7.29). In addition, U.S. farmers show a high level of acceptance of GM crop varieties. According to the U.S. Department of Agriculture, by 2010, most of the corn (86%), cotton (93%), and soybeans (93%) grown in the United States were GM varieties. However, more and more farmers outside the United States are also adopting these GM varieties.

Scientists are now developing many other GM crops, with traits including greater drought tolerance, improved storage potential, and better nutritional quality. One of the best-known examples of a GM crop with improved nutritional quality is “golden rice,” which produces b-carotene, a precursor to vitamin A. Since the first golden rice variety was developed, scientists have increased the b-carotene content of golden rice 23-fold. This concentration can make a difference in the lives of millions in developing countries who suffer from vitamin A deficiency, which can cause premature blindness (Figure 7.30). GM crops may have the potential to improve human health and provide food for a growing human population, but they have also engendered a great deal of controversy.

In addition to improved nutrition, proponents of GM crops indicate several ways in which they benefit the environment. A 2010 U.S. National Academy of Sciences study reports that insecticide use has decreased with increased planting of Bt corn and cotton. Herbicide-resistant crops can improve soil health, particularly where reduced tilling of fields lowers soil compaction and erosion (see page 215). These benefits, coupled with improved yields in the face of plant diseases and droughts, have the potential to improve food security.

211

On the other hand, skeptics of GM crops have identified several areas of serious concern. Pest and weed populations have developed resistance to Bt toxins and herbicides through natural selection. If the genes that confer herbicide resistance are transferred to weeds, they may become more difficult to control or may spread to non-GM crops and contaminate them genetically. Genes from GM corn have, in fact, been documented in the native varieties of corn in Mexico. Selection for herbicide tolerance has also been documented in “superweeds” that have become too costly to control. In addition, hundreds of insect populations have evolved resistance to Bt tolerance, and when pests targeted by Bt varieties decline, secondary pests that thrive in the absence of Bt-sensitive pests can increase.

Use of herbicide-resistant GM crops also means that farmers can use high levels of herbicides to control weeds without harming crops, but this can lead to unintended consequences. For example, widespread herbicide application has decreased milkweed abundance in North America, but milkweed is the sole host plant of the Monarch butterfly caterpillar, which is also now in decline. As more farmers use GM crops, the diversity of planted crops goes down and the number of monocultures goes up, both of which put crops at greater risk of destruction by pests.

212

Critics also worry that the widespread adoption of GM crops will take control of food production away from individual farmers and place it in the hands of a few biotechnology companies. They are concerned over the implications of this control to food security, food prices, and the economic welfare and independence of farmers.

Many consumers are concerned that GM foods may be harmful to human health. Although scientific reviews of GM crops have found no evidence that that they are unsafe, opponents of GM crops argue that there has been insufficient testing and that much of the testing has been done by industry researchers. They worry that conflicts of interest may compromise some of the research findings.

The development of GM crops has also raised philosophical issues. Some opponents of biotechnology argue that the blending of genes from different species is “unnatural,” creating so-called Frankenfoods. These critics suggest that moving genes from one species to another represents an unethical violation of natural processes. On the other hand, proponents of GM crops argue that biotechnology is a more targeted way to improve crop varieties, compared with the selective breeding techniques used to modify crops to become more palatable or more productive.

Some consumer advocates argue that labeling food made with GM crops, such as corn chips or soy oil, could be a way to move forward. For example, the European Union follows a mandatory labeling policy, whereby any food containing 0.9% or more GM ingredients must be labeled accordingly. And multiple polls have shown that over 80% of U.S. consumers favor labeling of GM foods as well. In the United States, however, the two responsible agencies, the U.S. Food and Drug Administration and the U.S. Department of Agriculture, do not support mandatory labeling of GM food because it implies that these products are nutritionally different from non-GM foods. Such labeling might lead to many consumers avoiding GM foods, resulting in higher food prices and losses of profit.

Still, U.S. consumers can avoid GM products at present (2015) by purchasing foods labeled as organic. As the controversy over GM crops continues (Figure 7.31), many food producers have begun labeling their products as GM-free, providing another way for U.S. consumers to make informed food purchases.