by Jeff Bessen
cartoon by Shannon McArdel

Before forming an opinion on genetically modified foods, one should understand what genes are in the first place. Knowledge of the history and biological function of genes helps explain why scientists are almost unanimous in their endorsement of the safety of GMOs.


If the genome of a cell is a bestselling novel – say, Harry Potter – then GMOs are a lot like an unauthorized second edition; perhaps one where Voldemort was caught and imprisoned, Dumbledore never died, and Harry and his friends had a grand and drama-free stint at Hogwarts.

I should explain. Every living cell has a unique set of instructions called a genome. If a genome is a book, and the millions of chemical units of DNA are the letters, then genes are the words. Groups of letters make up the words that tell a story or explain an idea; likewise, different arrangements of DNA letters make up genes. The cell’s genes collectively contain the instructions for how to make a cell, as well as the tools for the cell to accomplish every task it must perform. And, like a book, the genome only contains information as long as there’s something to read it – in the case of a book, your eyes and imagination turn the letters into the story, whereas DNA is deciphered by molecular machines called proteins.

What exactly are GMOs, and how do they fit into the metaphor? A GMO – short for ‘genetically modified organism’ – is a plant or animal that has had its DNA altered by people. According to our metaphor, scientists create GMOs by precisely changing some of the letters or words of the book – not by introducing some monstrous new technology, but simply by tweaking the cell’s own set of instructions so that it now behaves in a manner useful to humans. GMOs have proven to be enormously beneficial since their introduction over 30 years ago, especially in the realm of agriculture. Species of cash crops, for example, have been altered so that they now grow in difficult environmental conditions, contain more nutrients, or require fewer treatments of insecticide or herbicide.

GMOs are not found only in agriculture. For example, ZMapp, a promising new drug under study for curing Ebola, is produced in modified tobacco leaves, turning a greenhouse into a living pharmaceutical factory [1]. Microbes are similarly modified to perform many industrial tasks, and could one day be used to clean up oil spills or environmental toxins. Genetically modified mice and rats are crucial tools that scientists use to discover new drugs and prove that they are safe before starting human testing.

One question many people ask of GMOs is, are they safe to consume? We can answer this question in a simple way by referring to our metaphor. Would making small, precise edits to Harry Potter – so Dumbledore wears contact lenses instead of eyeglasses – dramatically change the overall meaning of the book? The odds are slim that such a small change would radically alter the entire text. Similarly, the odds of producing a toxic crop by mutating several of its DNA bases are extremely low. Researchers can say this with confidence because of the advances made in our understanding of cells made over the last century that have helped, bit-by-bit, to uncover what exactly genes are and how they operate.

What do we know about DNA that gives us confidence that our tinkering won’t produce something unsafe to humans? First, changes to DNA happen all the time in nature. Unlike a printing press that stamps out identical books one after the other, DNA is replicated by molecular machines that occasionally make errors. As living things grow, their cells divide, and the DNA must be replicated so that each new cell gets its own complete set of instructions. Each time this occurs, errors are made, and these errors are passed along to every subsequent daughter cell. In other words, all organisms – not just GMOs – contain modifications in their genome. Every plant or animal that you’ve ever consumed – not to mention every cell in your own body – contains these countless small DNA changes. Consuming organisms with modified DNA is not a creation of 21st century technology; it has been the reality for all of human history!

To further illustrate this point, most plants and animals we consume have already been genetically modified by humans. Historically, we have called this process breeding or artificial selection; GMO technology is simply an easier and more precise way for humans to do what they’ve already been doing for millennia. Those who have attempted a home garden know that their delicious produce requires constant tending to protect against weeds, insects, and rodents, and to ensure the plants have enough nutrients and water. How could such a defenseless and tempting plant survive on its own in the wild, let alone beat out its competitors? Before humans intervened, nothing like our modern domestic crops had ever existed, and they came into being only after humans deliberately chose the varieties with the most appealing genes. A farmer using seeds from her fastest growing plants for the next season, or mating cows with her strongest bull, is doing nothing less than assuring that her future plants or animals carry favorable genetic modifications. If the farmer wanted to bypass this slow, unpredictable process, she could have made those exact same changes in a laboratory, and the only difference would be that we now call the latter a GMO.

This brings up a final reason that we shouldn’t fear modified DNA: in most cases, the genetic edits that scientists make come straight out of nature’s playbook. Why invent a brand new way to kill insect pests when plants and other organisms have been devising and testing ways to defend themselves against pests for billions of years? For example, the microbe Bacillus thuringiensis is commonly found in soil, and it evolved a natural insecticide to kill insects that would feast on it. The nature of how this “Bt toxin” operates makes it completely harmless to humans [2]. Plants that have been modified to carry the Bt toxin gene are conferred the same protection from insects as the soil microbe, and therefore require fewer pesticides. Far from an affront to nature, GMOs are a way of borrowing nature’s ingenious solutions to problems that humans face.

It is easy to explain the theoretical reasons why GMOs should be no more dangerous than traditional food, but do studies of GMOs actually back up their safety? In a word: yes! No credible study has ever been published demonstrating health risks of GMOs [3]. Opponents do cite several studies that they claim prove the danger of GMOs. One notorious study from 2012 claimed that rats that were fed GMOs developed large tumors. The authors of the study were not as forthright in explaining that, for their study, they used mutant rats that were genetically more prone to developing cancer. For that and many other reasons, the study was repudiated by the journal in 2013 and retracted, although the was later republished elsewhere [4]. Another researcher from Russia claimed that feeding a diet of GMO soy to hamsters caused them to grow slower and become infertile. These findings should come as quite a shock to American farmers, who have been feeding GMO soy to livestock for over three decades, apparently without them becoming infertile. The Russian researcher also has never published his findings in a scientific journal, meaning no independent scientist has thoroughly analyzed his methodology or results; to date, the most reputable source for the hamster infertility study is the Huffington Post. By contrast, dozens of studies demonstrating the safety of GMOs have gone through the peer review process to ensure that their findings are accurate.

Why is it important that people understand what GMOs are? Polls of Americans show that a majority of the public is woefully uninformed about the topic. In the General Social Survey, Americans were asked if it was true or false that “ordinary tomatoes do not contain genes, while genetically modified tomatoes do;” nearly 5 in 10 answered “true.” [5] More recently, a survey from Oklahoma State University found that 80% of respondents supported “mandatory labels on foods containing DNA.” [6] (You should by now be aware that all food that originates from a plant or animal has DNA – and yes, even tomatoes.) This lack of awareness makes consumers especially vulnerable to marketing hype or scare tactics from opponents of GMOs, even though the vast majority of scientists agree on the safety of GMOs.

The unfounded fear of GMOs – born out of confusion about what DNA, genes, or GMOs even are – has had a dramatic and powerful impact on popular opinion and public policy. This month, Chipotle announced that it was removing GMOs from most of its menu. Earlier this year, the Massachusetts State House of Representatives began considering a bill that would require labeling of foods that contain GMOs. And while voluntarily avoiding GMOs is everyone’s prerogative, the fear underlying these anti-GMO measures is stifling the development of new technology. For example, a GMO salmon that grows larger and faster than traditional species – potentially saving resources and reducing the environmental impact of aquaculture – has been snarled in regulatory hurdles due to public outrage [7]. Continuing to shun GMOs, against the findings and advice of scientists, is thus a threat to the very technology that might allow humanity to feed a growing population in healthier and less resource-intensive ways. It’s like refusing to read the second edition of a book, with the mistaken belief that books are never to be edited – even though we know the first edition went through countless revisions prior to its arrival.

Jeff Bessen is a second year graduate student in the Chemistry and Chemical Biology PhD program at Harvard University.


[1] Pollack, A. October 2014. U.S. Will Increase Production of the Ebola Drug ZMapp, but May Not Meet Demand. The New York Times.

[2] Bacillius thuringiensis.

[3] European Comission. A decade of E.U.-funded GMO research.

[4] Casassus, B. Study Linking Genetically Modified Corn to Rat Tumors Is Retracted. Scientific American.

[5] Science and Technology: Public Attitudes and Understanding. National Science Foundation.

[6] Lusk, J. January 2015. Food Demands Survey.

[7] Van Eenennaam, A.L. & Muir, W.M. August 2011. Transgenic salmon: a final leap to the grocery shelf? Nature.

One thought on “Opinion–GMO: It’s easy as D-N-A!

  1. Great article. People fear GMOs because many don’t understand what it is and how exactly it affects the food we eat and so it is human nature to fear the unknown specially when there are ads claiming that GMO free food is much more safer. All we have to do is look at vegetables from a few decades ago and compare them to our vegetables today to understand the benefits of genetically modified food and why it is not risky.

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