A crowd of GMO and Monsanto protesters with signs at a rally in Pack Square in Asheville, North Carolina, on May 25, 2013. (Photo: J. Bicking/Shutterstock)

The world’s most commonly sprayed herbicide—glyphosate—is currently trapped in a familiar media cycle. The cycle goes something like this: 1) a report delivers bad news—the International Agency for Research on Cancer recently classified glyphosate as a probable carcinogen; 2) big media voices stoke outrage—Mark Bittman wrote that glyphosate should be taken off the market; 3) others try to offer perspective—Grist reminded us that “the list of things that probably causes cancer includes ... just about everything”; and, finally, 4) a concerned public becomes embroiled in a comment-section melee on social media.

This last venue matters, if only because it’s where the rhetoric of food reform is ultimately forged. It’s also a place where cooler heads rarely prevail. This is especially true when the topic is glyphosate, the active ingredient in Roundup, an herbicide produced by Monsanto to control weeds for genetically engineered crops. Glyphosate’s association with genetic modification dooms it to castigation. Despite the fact that toxicological experts downplayed the dangers of glyphosate in the wake of the IARC report, the bottom line for citizen experts is that, as Bittman writes, we’re being used “as guinea pigs for the novel chemicals that industry develops.”

How is it that so many highly intelligent people can so quickly agree with such a simplistic position? How is it that the opponents of genetic engineering—a process that Bittman himself admits appears safe—have so successfully demonized the plant breeding technique with so little evidence to do so? From whence comes this knee-jerk cynicism?

The simplest—and least interesting—answer is willful distortion. This kind of thing is, of course, commonplace when it comes to controversial subjects, so one need not dwell too much on hucksters who capitalize on the public’s genetic illiteracy to profit from a fear-driven and distorted agenda. But it’s also important to note that this strategy isn’t limited to opportunistic hacks. It happens in more mainstream political settings as well.

Central to the contagion system is an innate sense that the danger need not be visible, that limited contact with the substance transfers the entire risk, and that ingestion is the worst vector of infection.

I know this from firsthand experience. In 2012, when California was debating Proposition 37 (an initiative to label GMO foods—which I supported), I learned that a book I’d written on the history of pesticides was quoted by a pro-labeling California Right to Know video as an example of an endorsement of DDT (the video aimed to show how wrong experts have been in the past about substances once thought safe). But my book was thoroughly opposed to DDT. In fact, it was practically a paean to Rachel Carson. What California Right to Know did, though, was take the word “safe” from my book, pronounce that I had “reported” that “DDT is ‘safe,’” and situated the distorted quote between a doctor from the 1950s smoking a cigarette and a magazine story stating that agent orange was “harmless.” So there’s that tactic.

But the effectiveness of the anti-genetic engineering message hinges on something subtler. I’m hypothesizing, but I think the message touches ancient neurological wiring. The University of Pennsylvania psychologist Paul Rozin, who studies human food preferences, argues that we have a built in “contagion system” to evaluate contamination. The immediate impulse to register disgust in the face of something putrid—and thus dangerous—derives from this system. Central to the contagion system is an innate sense that the danger need not be visible, that limited contact with the substance transfers the entire risk, and that ingestion is the worst vector of infection. All these qualities evolved to help protect humans from eating the wrong things.

Genetically modified food protesters hold up a sign calling Monsanto "MonSATAN"at a GMO protest rally on May 25, 2013, in downtown Asheville, North Carolina. (Photo: J. Bicking/Shutterstock)

Not incidentally, these are also the very qualities that mark genetically modified ingredients. Unseen, rumored to be dangerous irrespective of dose, and often ingested unknowingly (without labels), the mere idea of these ingredients may very well tap our instinct-driven disgust response and, in turn, explain the unusually vitriolic reaction we have to a technology that (ironically) accounts for ingredients in 70 percent of the processed foods we eat.

While it might seem implausible that a plant-breeding technique could elicit the same manner of reaction as, say, a rotting carcass, note how opponents of genetically engineered ingredients rhetorically package their message. They explicitly highlight the theme of contagion. In a typical example, Seattle Organic Restaurants recently published an article titled, “GMO Rice Contaminates the World Rice Supply and Dr. Vandana Shiva Compares GMO Contamination to Bio-Rape.” The piece centers on the “research” of an organization called “GM Contamination Register,” which records “contamination incidents” whereby GE and non-GE ingredients are mixed. Shiva, who is reportedly paid up to $40,000 an appearance to speak of bio-rape, routinely links genetic “contamination” to diseases such as autism. There is no medical evidence for this linkage, but the suggestion alone helps transfer the plant-breeding technique from the realm of science to the realm of food, where it becomes fair game for the contagion system to evaluate.

In its more extreme form, the rhetoric used to promote disgust against genetically modified foods goes overtly scatological. You can buy a bumper sticker on Amazon.com that declares, “Ban GMOs: That Shit Ain’t Food.” Typical comment sections routinely include expressions such as “perhaps there are some people out there who WANT to eat that GMO shit” or, as Farmwatch explained on its Facebook page, “Many farmers grow this GMO crap.” Granted, the words “crap” and “shit” are used as generic expressions of negativity rather than actual references to scat, but our contagion system, forged before the advent of language itself, doesn’t know the difference. Past hardwiring can shape present thoughts—and it can affect how we react to food.

Nobody is saying we shouldn’t be concerned about glyphosate. But when leading scientists react to the IARC move with comments such as “The IARC report does not raise immediate alarms” and “the weight of evidence is against carcinogenicity” and “this report is not a cause for undue alarm,” it seems a rush to judgment to declare humanity guinea pigs for a substance that should be taken off the market. More to the point, while we (thankfully) have no choice but to trust our guts about what disgusts us as consumers seeking food, we need to remind ourselves that overblown rhetoric can contaminate our judgment just as easily as it can our food choices.

The Things We Eat is a regular Pacific Standard column from James McWilliams on food, agriculture, and the American diet.