It happened slowly, and then all at once.

First came White Castle’s Impossible slider, which Eater NY’s Ryan Sutton hailed as “one of America’s best fast-food burgers” in 2018. That slider just happened to be meatless, containing an Impossible Foods-branded patty made from soy protein, potato protein, coconut oil, sunflower oil, and heme, the ingredient that gives the burger the taste, aroma, and “bleed” of a juicy beef patty. Then, the floodgates opened: In January, Carl’s Jr. became the largest American fast-food chain to offer plant-based patties made by Beyond Meat in 1,100 locations nationwide; just a few months later, Burger King, Del Taco, and the fast-casual chain Qdoba have followed suit with fake-meat offerings of their own, from Whoppers to tacos to burrito bowls.

But conspicuously missing from the growing list of fast-food chains offering plant-based “meats” produced by brands like Impossible Foods and Beyond Meat is McDonald’s, the biggest quick-service chain in the U.S.

Del Taco wasn’t the only one to take notice of the lack of Golden Arches among the mock-meat herd. Following Burger King’s announcement that the brand is testing Impossible meatless burgers in St. Louis (with potential for a national rollout), a Change.org petition urging McDonald’s to add “a healthy, meatless option” has regained traction, even getting the endorsement of Ellen DeGeneres (ranking somewhere between British children going viral and midwestern moms dancing on TV). “McDonald’s is being left behind by its biggest rival — who is demonstrating that a national fast-food chain must cater to a new generation of consumers by offering a healthy and tasty meat-free burger,” wrote the petition’s creator, vegan author Kathy Freston.

Freston and the 165,000+ petition signers needn’t worry. At this point, it seems like a foregone conclusion that McDonald’s will eventually start offering meatless burgers in the U.S.

Fast food is a natural fit for test-tube “meat”

The most obvious use case for lab-optimized “meat” is to replace the lab-optimized meat commonly used in fast food, as New York Times opinion writer Jamelle Bouie tweeted earlier this week.

Take Del Taco’s seasoned beef. Beyond the core component, ingredients include lots of spices as well as fillers like textured vegetable protein (rival taco chain Taco Bell famously fought back against a class-action lawsuit in 2011 by flexing about the brand’s “88 percent quality USDA-inspected beef”). Burger chains like McDonald’s tout patties made with “100 percent real beef” and “no fillers, no additives, no preservatives,” but stop short of completely eliminating the use of hormones and antibiotics.

That’s all to say no one’s expecting superior-grade meat when cruising through the drive-through at 1 a.m. Plant-based “meat” like Impossible’s — Frankensteined from soy protein concentrate and other ingredients — won’t make much of a difference to the point that most consumers might not even notice. As Tim Carman at the Washington Post proclaimed, Burger King’s Impossible Whopper patty “has more flavor than the meaty one.”

More Americans are embracing plant-based alternatives

While the percentage of Americans who identify as vegan or vegetarian hasn’t increased drastically, according to a 2018 Gallup poll, sales of plant-based food are climbing. Per data collected by Nielsen and the Good Food Institute, the category grew 8.1 percent between 2016 and 2017. That indicates that Americans aren’t necessarily giving up meat and other animal products completely, but are hungry for alternatives. Perhaps this is due to ethical or environmental concerns...or maybe they just subscribe to Beyonce’s strain of on-again, off-again veganism.

Whatever the reason, plant-based food presents a huge market opportunity — to the tune of $3.1 billion in 2017. McDonald’s, which has struggled to grow traffic in the U.S., would be wise to get in on that meat-free pie to attract new customers.

The age of the meatless burger is upon us, we just don’t realize it yet

McDonald’s domestic traffic struggles notwithstanding, there’s no denying that the chain still reigns supreme, with enviable sales growth and a ubiquitous overseas presence (more than 36,000 restaurants worldwide, according to the company). But more than that, the burger chain remains an American icon, those familiar twin golden arches an emblem of global capitalism, unfettered consumerism, and the United States itself. (Look closely and you might notice Richard and Maurice McDonald’s faces carved into Mount Rushmore beneath Roosevelt.)

Burger King’s partnership with Impossible Foods is undoubtedly a major step into popular culture for mock meat; McDonald’s, when that day comes, will mark the true mainstreaming of plant-based food. Other brands would be sure to follow suit, as was the case when McDonald’s vowed to stop serving chicken raised with “human” antibiotics in 2015. Shortly after, Costco — that warehouse of rotisserie chicken, coffins, and other delights — and Subway, among other competitors, also announced a shift away from antibiotics. Such is the power of being one of the largest global buyers of beef and chicken: Anything McDonald’s does is sure to have outsize influence in the industry.

When reached for comment, McDonald’s, Impossible Foods, and Beyond Meat all declined to confirm or deny if a partnership is in the works, but Lucy Brady, McDonald’s senior vice president of corporate strategy, revealed at Fortune’s Most Powerful Women Next Gen Summit in December that “plant-based protein is something we’re keeping our eye on.” (McDonald’s, mind you, already offers a McVegan burger in Sweden and Finland.)

A non-answer, but no matter: Whatever McDonald’s mouthpieces might be willing to say out loud now are nearly beside the point anyway, since the question is no longer if, it’s when.