Scare stories on ‘uncontrolled spread’ of GMOs spreading uncontrollably: They’re misguided

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The local food co-op in my town has a store that contains numerous “Non GMO” signs, and prominently displays signs proclaiming that a product is “organic”. The store buys some small fraction of their produce from local farmers. There are quite a few co-op stores like this in New England. However, this co-op has a website that hosts blogs written by their employees. One day, a new blog entry appeared, that opened with these words:

Genetically modified organisms (GMO) are certainly getting their share of the headlines these days.  While the debate about the health issues associated with GMO rages on and arguments over how we will feed the world’s population continue to consume the discussion, one thing is very clear in my mind: the environmental impacts of these crops have the potential to change the planet as we know it. …

The point is GMO crops (even currently unapproved ones) are starting to pop up in more and more unexpected places. If genetically engineered species have the opportunity to spread they could threaten the biodiversity of our agricultural systems or even our ecosystems.

There are plenty of other stories on the web that predict the uncontrolled spread of genetically modified plants or claim that it is happening now.Screen Shot 2015-10-26 at 7.16.13 PM

Here is a statement that appeared in a discussion forum on

To start the discussion I’ll list my humble opinions:

  • GMO is not a natural propagation, (man-made origin). GMO crops are therefore not native to any ecosystem.

  • Farmers being sued and taken over by business growing GMO crops that contaminated or “invaded” the non-GMO crop are examples of altered business opportunities.

  • Decrease in beneficial insects and increase in weed resistance are environmental impacts and

  • Likely human health impact is still unknown, therefore should be considered harmful until proven otherwise

Some years ago Scientific American raised the question of the possible threat of invasive GMO plants, and cited the ubiquitous presence of volunteer GMO canola plants across North Dakota, far from any canola fields. But finding a plant that has germinated far from any field does not mean it is invasive, it just means a seed got really lucky.


The genetics of GMO plants tells us at a very fundamental level that inserting or removing a specific trait in a plant is not going to make it invasive. Therefore, I just could not let the blog on the co-op’s website go unanswered. I voted with my feet and my keyboard, reducing my purchases at that store to zero, and I wrote a reply to the blogger, which appears below in a slightly modified form from my original reply.


What is an invasive species?

At least 160 species of plants and animals have been introduced into North America in the last 600 years since the landing of Europeans on American soil. Some of these plants and animals have made America what it is today, while many are obscure species with no obvious impact on our land. There have probably been many more species introduced to North America during that time that have not been identified as “imported”, because many species have not been extensively studied.

There are reasons why a few introduced species, such as tumbleweed, Johnson grass, kudzu, and hydrilla are familiar weeds to people in many areas of the country, while many other introduced species are rarely found anywhere. Tumbleweeds are the iconic yet unwanted symbol of the American West. Johnson grass is public enemy #1 of most suburban dwellers across much of the southern United States and is at the same time is widely used for forage and hay for livestock. Hydrilla is an extremely invasive water plant that is choking Florida’s waterways. Eucalyptus trees grace many southern California cities and towns. Vetch is an important legume used in crop rotations and as a livestock feed. Kudzu has been spreading across the southern U.S. at the rate of 150,000 acres per year, choking out native vegetation.


The familiar house sparrows, starlings, and pigeons that populate our cities were all “imported”, as were some types of bees, mites, moths, and mosquitoes. Horses were brought to America centuries ago by Europeans; today horses are a large part of contemporary culture in many areas of the U.S. So some introductions have been welcome contributors to our land and our culture, while others not so much.

New species with traits quite different from species that are already present are likely to either out-compete, and eventually displace, existing species, or they will be so completely unsuited that they will die quickly. Tumbleweeds, kudzu, and Johnson grass have been incredibly successful in quickly spreading across all the land within broad climatic zones. Hydrilla has choked waterways to the extent that motorboats cannot be operated in those waters. Homeowners in many areas of the country annually fight to prevent Johnson grass from overtaking their lawns and flowerbeds. Tumbleweeds soak up precious ground water in arid areas of the western U.S., limiting the amount of grass that grows that can feed both wildlife and cattle, and retain the topsoil. Tumbleweeds have spread rapidly, not because they are drought-tolerant, but because of the unique method they have to spread their seed. This allowed tumbleweed to spread dozens of miles or more every growing season after their initial introduction; within a few decades they covered much of western U.S. Hydrilla is taking over Florida waterways because there are no fish or other aquatic animals in Florida that will eat the hydrilla, and because it grows extremely fast. Johnson grass spreads by underground rhizomes, and is not killed by fire or heavy grazing or repeated mowing- all actions that will kill many other weeds.

What are the differences between GMOs and invasive species?

There is a very important difference between GMO crops and invasive imported plants like tumbleweed and hydrilla. Existing GMO crops do not create plants that have characteristics that will cause them to overrun other plants. In the case of Bt corn, being able to resist certain insects will give Bt corn an advantage (temporarily) over non-Bt corn, but Bt corn is still corn – it will only grow where corn can grow now. A glyphosate-resistant crop has no advantage over the non-glyphosate-resistant version of the same species in an uncultivated setting, since being glyphosate resistant is neither helpful nor detrimental to the plant “in the wild”.

In fact, being glyphosate resistant causes the plant to expend slightly more energy during the growing season than does a non-glyphosate-resistant variety of the same plant. (This would be a very tiny difference – something that could be detected in a sophisticated lab – maybe.) However, over the course of many years, the glyphosate resistant genes would slowly disappear (there is much evidence that organisms tend to get rid of “unnecessary” genes over the span of thousands of generations, due to the fact that random mutations to those non-essential genes destroys the genes but does not impact the ability of the plant to survive.) All of the genes inserted into GMO crops are “non-essential”, which is to say that the plant will grow just as well without the extra genes as with the genes. Thus, if we scattered our GMO seed into an undisturbed area and came back a thousand years from now, we would likely find that the GMO genes had mutated so as to become non-functional, or they might have disappeared entirely. There are many examples of this type of gene selection that have been well studied by many laboratories.


An exception is a genetic modification that preserves the species, such as was the case with Hawaiian papaya. Virus resistance may preserve the yellow squash, although squash is an “artificial” plant that exists only because humans created it. Oranges are a plant variety that is now seriously threatened by a virus; it likely can be saved only by genetic modification. Thus, genetic engineering can preserve species that would otherwise disappear.

Related article:  Fitness and health expert: 10 science-based reasons why I'm thankful for GMOs

Another very important difference between the invasive imported plants and GMO crops is that the new species are genetically very different from existing plants. “Very genetically different” means that the plant has many thousands of genes that are very different from the plant species that already exist in a location. Individual mutations (which occur constantly in the genes of all plants and animals including ourselves) do not radically change the overall characteristics of the plant. GMO plants differ from the non-GMO variety of the same plant by only a very few genes.

Bt corn has one additional gene that provides the “instructions” for making Bt toxin. The Bt gene has no other functionality. It does not change the plant’s preference for soil type, temperature, water, or sunlight. Bt plants will grow only where non-Bt plants of the same variety will grow.

Glyphosate resistant plants contain an additional gene that is slightly different from the naturally occurring gene. The additional gene specifies a slightly different version of the same enzyme that is specified by the naturally occurring gene, and the modified enzyme does the same exact function as the naturally occurring enzyme, but it works even when it is exposed to glyphosate, while the naturally occurring enzyme does not function in the presence of glyphosate. Thus, glyphosate-resistant plants have no functionality that is in any way different from the non-glyphosate-resistant plant of the same variety.


Apples have four genes that produce the chemical that causes sliced apples to turn brown almost immediately. The new Arctic Apples have those four genes altered so they are not functional. Apples have over 57,000 genes, so four genes is a very tiny part of the total genomic content of the plant – a very tiny change in the overall genetics of the plant. (Corn has about 32,000 genes.)

These modified apples are generally as insect resistant as non-modified apples, but one insect that eats apples has shown some preference for the modified apples (apparently it does not like the chemical that causes browning). A slight preference by insects for the modified apples would likely result in the trees bearing modified apples eventually disappearing if they were left with trees bearing non modified apples in a non-cultivated field for perhaps thousands of years, since the apple trees carrying the deactivated gene would be at a competitive disadvantage due to that insect.

A more valid concern about a GMO plant becoming an invasive species could be directed at modifications that cause the plant to become more drought-tolerant. This type of modification would allow the plant to grow in areas it could not previously grow, and thus compete with existing plants in the area. Drought-tolerant GMO varieties have great promise as important food crops, either by allowing the same crop to be grown in the same place as now, but with less water, or to be grown in places the crop cannot now be grown. However, food crops grow abundantly only under the artificial conditions of cultivation (with the exception of some berry crops), and seldom are found in large stands in non-cultivated areas. This is because almost all food crops are plants that have been extensively altered from their original wild ancestors, and they have been selected to grow well under human-designed cultivation conditions, rather than “wild” conditions. (At present, there are no drought-tolerant crops being grown, but drought-tolerant rice has been developed. Drought-tolerance is a trait that would clearly help nations feed their people if the global climate continues to warm in the future as much as it has over the past 100 years.)

Are there ecological problems ahead?

To summarize, ever since Europeans first landed on America’s coastlines people have been intentionally and unintentionally introducing new species of plants and animals to North America. The introduction of these new species in some cases radically changed the ecology of many areas of the U.S. The introduction of these new species has also given us “experiments” from which we have learned much about the abilities of a new plant or animal to survive and prosper in its new environment. The “experiment” has run, in some cases, hundreds of years. While there is no question that imported species have radically altered North America over the last 600 years, it is clear that the environment has not been “catastrophically” altered. GMO crops, being so very similar to the non-GMO crops, do not have the capability to wrought the immense changes to the landscape as were caused by plants like tumbleweeds.


In the case of corn, the corn we eat today is very different from the corn our ancestors might have eaten at the first Thanksgiving Dinner. Those differences are the result of human interventions, and those changes were developed by accident, or trial-and-error experiments, with no knowledge of what genes were being substituted for what other genes. The resulting corn plant did not develop into an invasive weed, but rather into a critically important source of food that grows poorly if at all in uncultivated environments. Additional modifications will come in the future to make corn grow more efficiently (take less land and less water) and thus be more environment-friendly than today’s corn.

Corn is a clear example of a genetically engineered crop which has become commonplace in the American landscape, and has had zero negative ecological impact.

Based on the history of plants that have been imported to North America, and the science of genetics that is the basis for the development of new varieties of plants, there will be no long-term negative ecological consequences that will arise from the development and use of GMO crops.  In fact, there will likely be some very significant reductions in the environmental impact of agriculture with the development and use of more GMO crops in the future.

Roy Williams, former software engineer on a variety of projects including the Space Shuttle, Landsat Satellite, and Doppler weather radar, and retired dairy farmer, and  now PhD student  in Molecular and Cellular Biology at Dartmouth College, Department of Immunology and Department of Biomedical Data Science. Follow him on Twitter @RoyWilliams1024

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