Figure 1. The symptoms of papaya ringspot virus are shown on the tree (a) and fruit (b). “This work” is in the Public Domain, CC0.

In the early 1990s, an emerging disease destroyed Hawaii’s papaya production and threatened to decimate the $11 million industry (Figure 1). Fortunately, Dennis Gonsalves, raised on a sugar plantation and then became a plant physiologist at Cornell University, would develop papaya plants genetically engineered to resist the deadly virus. By the end of the decade, the Hawaiian papaya industry and the livelihoods of many farmers were saved thanks to the free distribution of Dr. Gonsalves’s seeds.

Developing a new crop strain is an example of agricultural biotechnology: a range of tools that include both traditional breeding techniques and more modern lab-based methods. Traditional methods date back thousands of years, whereas biotechnology uses the tools of genetic engineering developed over the last few decades. Genetic engineering is the method scientists use to introduce new traits to an organism. This process results in genetically modified organisms or GMOs. For example, plants may be genetically engineered to produce characteristics to enhance food crops’ growth or nutritional profile. GMOs that are crop species are commonly called genetically engineered crops, or GE crops for short.

The History of Genetic Modification of Crops

Nearly all the fruits and vegetables in your local market would not naturally occur. In fact, they exist only because of human intervention that began thousands of years ago. Humans created the vast majority of crop species using traditional breeding practices on naturally occurring wild plants. These practices rely upon selective breeding (human assisted-breeding of individuals with desirable traits). Traditional breeding practices, although low-tech and straightforward to perform, have the practical outcome of modifying an organism’s genetic information, thus producing new traits.

An interesting example is maize (corn). Biologists have discovered that maize was developed from a wild plant called teosinte. Through traditional breeding practices, humans living thousands of years ago in what is now Southern Mexico began selecting for desirable traits until they could transform the plant into what is now known as maize. In doing so, they permanently (and unknowingly) altered its genetic instructions, allowing new traits to emerge. Considering this history, we might ask whether such a thing as “non-GMO” maize exists.

Figure 2. A wild grass called teosinte was genetically modified through selective breeding to produce what is now known as maize (corn). This transformation process started thousands of years ago by the indigenous people of what is now Mexico. “This work” by Nicolle Rager Fuller, National Science Foundation, is in the Public Domain, CC0.
Figure 3. Brassica oleracea is a plant in the mustard family and is known as wild cabbage. From it were developed many familiar crops, such as cauliflower, broccoli, Brussel sprouts, and of course, cabbage.“Brassica oleracea wild” by Kulac is licensed under CC BY-SA 4.0

This history of genetic modification is common to nearly all crop species. For example, cabbage, broccoli, brussel sprouts, cauliflower, and kale were all developed from a single species of wild mustard plant (Figure 2). Wild nightshade was the source of tomatoes, eggplant, tobacco, and potatoes, developed by humans 7,000 – 10,000 years ago in South America.

Traditional Breeding v. Modern Genetic Engineering

To produce new traits in livestock, pets, crops, or other organisms, there almost always has to be an underlying change in that organism’s genetic instructions. What many people might not understand is that traditional breeding practices do, in fact, result in permanent genetic changes and is, therefore, a type of genetic modification. This misunderstanding may arise because traditional breeding practices do not require sophisticated laboratory equipment or any knowledge of genetics, which some may see as a prerequisite for genetic modification.

How do traditional breeding practices compare to modern genetic engineering? Both result in changes to an organism’s genetic information, but the magnitude of those changes varies among the two techniques (Figure 3). Traditional breeding shuffles all the genes between the two organisms being bred, which can number into the tens of thousands (maize, for example, has 32,000 genes). The results can be unpredictable when mixing such a large number of genes. Modern genetic engineering is more precise because scientists can modify a single gene. Also, genetic engineering can introduce a gene between two distantly-related species, such as inserting a bacterial gene into a plant. Such transfer might seem unusual, but it is not without its equivalent in nature. In horizontal gene transfer, DNA from one species can be inserted into a different species. One recent study, for example, has found that humans contain about 150 genes from other species, including bacteria.

Image result for Michael J. Ermarth (Methods of Plant Breeding) Wikimedia Commons.

Figure 4. Both traditional breeding and modern genetic engineering produce genetic modifications. Genetic engineering allows for fewer and more precise genetic modifications. FDA graphic by Michael J. Ermarth (Methods of Plant Breeding) [CC0 Public Domain], via Wikimedia Commons.

Potential Benefits of Genetic Engineering

Enhanced nutrition

Figure 5. White rice and Golden rice. Genetically engineered “Golden Rice” contains up to 35 μg β-carotene per gram of rice, which could prevent millions of cases of blindness worldwide.

Advances in biotechnology may provide consumers with nutritionally enriched foods (Figure 4), longer-lasting, or lower levels of certain naturally occurring toxins present in some food plants. For example, developers use biotechnology to reduce saturated fats in cooking oils, reduce food allergens, and increase disease-fighting nutrients. Biotechnology may also be used to conserve natural resources, enable animals to use nutrients in feed more effectively, decrease nutrient runoff into rivers and bays, and help meet the increasing world food and land demands.

Cheaper and More Manageable Production

Biotechnology may provide farmers with tools to make production cheaper and more manageable. For example, some biotechnology crops can be engineered to tolerate specific herbicides, which makes weed control simpler and more efficient. Other crops have been engineered to be resistant to specific plant diseases and insect pests, which can make pest control more reliable and effective and/or can decrease the use of synthetic pesticides. These crop production options can help countries keep pace with demands for food while reducing production costs.

Improved pest control

Biotechnology has helped make pest control and weed management safer and easier while safeguarding crops against disease. For example, genetically engineered insect-resistant cotton has significantly reduced the use of persistent, synthetic pesticides that may contaminate groundwater and the environment. In terms of improved weed control, herbicide-tolerant soybeans, cotton, and corn enable the use of reduced-risk herbicides that break down more quickly in soil and are non-toxic to wildlife and humans.

Potential Concerns about Genetically Engineered Crops

The complexity of ecological systems presents considerable challenges for experiments assessing GE crops’ risks and benefits. Assessing such risks is difficult because both natural and human-modified systems are highly complex and fraught with uncertainties that may not be clarified until long after an experimental introduction has been concluded. Critics of GE crops warn that their cultivation should be carefully considered within broader ecosystems because of their potential environmental benefits and hazards.

In addition to environmental risks, some people are concerned about the potential health risks of GE crops because they feel that genetic modification alters an organism’s intrinsic properties or essence. As discussed above, however, it is known that both traditional breeding practices and modern genetic engineering produce permanent genetic modifications. Further, traditional breeding practices actually have a larger and more unpredictable impact on a species’ genetics because of its comparably crude nature. Considering this, it is wise that both new GE crops and traditionally produced crops should be studied for potential human health risks.

To address these various concerns, the US National Academies of Sciences, Engineering, and Medicine (NASEM) published a comprehensive, 500-page report in 2016 summarizing current scientific knowledge regarding GE crops. The report, titled Genetically Engineered Crops: Experiences and Prospects, reviewed more than 900 research articles, in addition to public comments and expert testimony. Results from this seminal report, hereafter referred to as the “GE Crop Report” for brevity, are shared in the subsections below.

Interbreeding with Native Species

Through interbreeding or hybridization, GE crops might share their genetically-modified DNA with wild relatives. This could affect the genetics of those wild relatives and have unforeseen consequences on their populations, and it could even have implications for the larger ecosystem. For example, if a gene engineered to confer herbicide resistance were to pass from a GE crop to a wild relative, it might transform the wild species into a ‘super weed’ – a species that the herbicide could not control. Its rampant growth could displace other wild species and the wildlife that depends on it, thus inflecting ecological harm.

NASEM’s GE Crop Report did find some evidence of genetic transfer between GE crops and wild relatives. However, there was no evidence of ecological harm from that transfer. Clearly, continued monitoring, especially for newly-developed crops, is warranted.

 Consumer’s Right to Choose 

The International Federation of Organic Agriculture Movement has made stringent efforts to keep GE crops out of organic production. Yet, some US organic farmers have found their corn (maize) crops, including seeds, contain detectable levels of genetically engineered DNA. The organic movement is firmly opposed to any use of GE crops in agriculture, and organic standards explicitly prohibit their use (however, keep in mind that even “organic” maize has incurred significant genetic modification compared to its wild relative, teosinte). The farmers whose seed is contaminated have been under rigid organic certification, ensuring they did not use any genetically modified materials on their farms.

Any trace of GE crops must have come from outside their production areas. While the exact origin is unclear, the contamination has likely been caused by pollen drift from GE crop fields in surrounding areas. However, the contamination may have also come from the seed supply. Seed producers, who intended to supply GE crop-free seed, have also been confronted with genetic contamination and cannot guarantee that their seed is 100% GE crop-free.

Long-Term Ecological Effects

An early study indicated the pollen from a particular type of genetically modified corn might be harmful to the caterpillars of monarch butterflies, This type of corn, known as Bt corn, is genetically modified to produce a bacterial protein that acts as an insecticide. This trait is favorable because it reduces the amount of insecticides farmers use. Pollen from Bt corn can harm caterpillars, but only at very high concentrations. These concentrations are seldom reached in nature, and follow-up studies have found the effect of Bt corn to be negligible.

NASEM’s GE Crop Report documents that other scientists questioned the validity of that initial monarch study, ultimately leading to a large, multi-national study funded by the US and Canada. They found that the vast majority of Bt corn grown did not represent a risk to monarchs. However, one strain of Bt corn did and was consequently removed from the market.

The GE Crop Report also mentioned a separate threat to monarchs: loss of milkweed, which is critical to the butterfly’s lifecycle. Some GE crops are engineered to resist the herbicide glyphosate. Farmers using these crops can spray their entire field with the herbicide, which kills milkweed but not their GE crop. This can lower the amount of milkweed growing within the habitat range of monarchs. The report concluded that more studies are needed to quantify the actual impact this may be having on monarch populations.

Human Health Risk

At least some of the genes used in GE crops may not have been used in the food supply before, so GM foods may pose a potential risk to human health, such as producing new allergens. But this is also true of crops generated by traditional breeding practices (because both produce genetic modifications and thus new traits).

Like other ‘controversial’ scientific issues, the scientific consensus on GE crops is quite clear: they are safe. The UN’s Food and Agriculture Organization has concluded that GMOs’ risks to human and animal health are negligible. NASEM’s GE Crop Report found “no substantiated evidence of a difference in risks to human health between current commercially available genetically engineered (GE) crops and conventionally bred crops, nor did it find conclusive cause-and-effect evidence of environmental problems from the GE crops.” The American Medical Association’s Council on Science and Public Health 2012 stated that “Bioengineered foods have been consumed for close to 20 years, and during that time, no overt consequences on human health have been reported and/or substantiated in the peer-reviewed literature.” Similar statements have been made by the US National Resource Council and the American Association for the Advancement of Science, which publishes the preeminent scholarly journal Science.

The potential of GE crops to be allergenic is one of the potential adverse health effects, and it should continue to be studied, especially because some scientific evidence indicates that animals fed GE crops have been harmed. NASEM’s GE Crop Report concluded that when developing new crops, it is the product that should be studied for potential health and environmental risks, not the process that achieved that product. What this means is because both traditional breeding practices and modern genetic engineering produce new traits through genetic modification, they both present potential risks. Thus, both should be adequately studied for the environment’s safety and human health.

Intellectual Property Rights

Intellectual property rights are one of the important factors in the current debate on GE crops. GE crops can be patented by Agri-businesses, leading to them controlling and potentially exploiting agricultural markets. Some accuse companies, such as Monsanto, of allegedly controlling seed production and pricing, much to the detriment of farmers. NASEM’s GE Crop Report recommends more research into how a few companies’ concentration of seed markets and the subsequent reduction of free market competition may affect seed prices and farmers.

It should be noted that crops developed by traditional breeding can also be legally protected and controlled in ways similar to GE crops. From Oregon State University, Jim Myers notes, “In all but a few cases, all contemporary varieties developed by private breeders are [legally] protected, and most public varieties are protected as well.”

Are GE Crops the Solution We Need?

Significant financial and intellectual resources have been allocated to answering the question: are GE crops safe? After many hundreds of scientific studies, the answer is yes. But a significant question still remains: are they necessary? Certainly, such as in instances like Hawaii’s papaya, which was threatened with eradication due to aggressive disease, genetic engineering was a quick and effective solution that would have been extremely difficult, if not impossible, to solve using traditional breeding practices.

However, in many cases, the early promises of GE crops – that they would improve the nutritional quality of foods, confer disease resistance, and provide unparalleled advances in crop yields – have largely failed to come to fruition. NASEM’s GE Crop Report states that while GE crops have resulted in the reduction of agricultural loss from pests, reduced pesticide use, and reduced rates of injury from insecticides for farm workers, they have not increased the rate at which crop yields are advancing when compared to non-GE crops. Additionally, while there are some notable exceptions, like golden rice or virus-resistant papayas, very few GE crops have been produced to increase nutritional capacity or to prevent plant disease that can devastate a farmer’s income and reduce food security. Most GE crops are developed for only two purposes: to introduce herbicide resistance or pest resistance.

Genetic engineering of crops represents an important tool in a world of rapidly changing climate and a burgeoning human population. Still, as you will see in the next chapter, it is only one of many tools that agriculturists can use to produce enough food for all humans while simultaneously working to conserve the environment.

Suggested Supplementary Reading:

NASEM. 2016.Genetically Engineered Crops: Experiences and Prospects.


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Introduction to Environmental Sciences and Sustainability Copyright © 2023 by Emily P. Harris is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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