One day soon, nearly every egg you eat will be “cage-free.” A long campaign by animal-welfare groups to improve the lives of factory-farmed chickens has ended in a rout. McDonald’s announced last September that it plans to get all of its eggs for restaurants in the U.S. and Canada from cage-free hens within the next decade. (The change will affect 8 million hens per year.) In the months since then, hundreds of other fast-food chains, food-service companies, and supermarkets, including each of the nation’s top 25 grocery companies, have made similar commitments. According to a recent front-page story in the Washington Post by Karin Brulliard, egg-industry representatives now concede that the eventual and utter abandonment of battery-cage production methods is “a fait accompli.”

If the cage-free switch marks a major victory for activists, it’s just as notable for what it says about the movement’s changing priorities. Not so long ago, the abuse of chickens barely registered as a worthy target for animal-welfare campaigns. The suffering of cats and dogs seemed more pressing and more tractable, as did the mistreatment of simians in research labs, elephants in circus acts, and the use of furry animals for making clothing and cosmetics. But in the past 15 years or so, the welfare groups have begun to dabble in a novel way of thinking—one that claims to favor level-headed calculations over passion-fueled outrage. Forget the cats, these number-crunchers said. Save the poultry.

How did the activists arrive at chicken rights? For activist Paul Shapiro, who founded a group called Compassion Over Killing in 1995 while still a high school student in Washington, D.C, it started with an essay. Up until 2000, he’d focused his group’s efforts at familiar targets—the fur industry, research labs, Ringling Bros. and Barnum & Bailey. Then Shapiro read a piece by Matthew Ball, at the time the executive director of Vegan Outreach. Ball counseled activists that they could do more good for animals by adopting a fierce but dispassionate utilitarianism. “Rather than focus on what appeals to (or offends) us personally,” he wrote, “we can challenge ourselves to approach advocacy through a straightforward analysis of the world as it is, striving solely to alleviate as much suffering as possible.”

One figure in particular caught Shapiro’s eye: According to Ball, nearly 99 percent of all the animal killings in the U.S. occur in the food industry, and the suffering those creatures endure on farms can be intense. Shapiro liked Ball’s idea of maximizing benefit for animals. At the time, he says, none of the animal-welfare groups were doing very much at all about conditions on factory farms, though many advocated for vegetarianism or veganism.

So Shapiro called a meeting of his top volunteers and asked them to read Ball’s essay. They all agreed, based on the vastly disproportionate number of lives at stake, that they could make the biggest difference by working to help farmed animals. But which farmed animals in particular? Again they number-crunched the suffering: Every year, 29 million cattle and 115 million hogs are killed for meat; meanwhile, 8.8 billion chickens die. That’s a staggering inequity of carnage, with 60 slaughtered birds for every single cow or pig.

There were other reasons for Shapiro and his team to choose the chicken crisis. The federal law governing humane slaughter, first passed in 1958, does not apply to poultry. And while cattle spend the first part of their lives on pasture, Shapiro says, egg-laying chickens live their two years inside a warehouse in a tiny wire cage. They never feel the sun; they never touch the earth; they never get a chance to spread their wings. These birds “are the greatest victims of humanity’s exploitation of land animals,” he told me. Compassion Over Killing first visited an egg factory in 2001, on the Eastern Shore of Maryland. “They were rotting in their cages, getting trapped in the wires, and dying of dehydration while inches away from water,” Shapiro said. “I’m for the underdog,” he added. “The under-rodent, the under-chicken.”

By championing the chicken, Shapiro said in an 2003 interview, he’d hoped to optimize his activism, to get “the biggest bang for the buck.” Shapiro’s group had already turned more businesslike in other ways: Shapiro cut off his dreadlocks and put away his wallet chain; he no longer tried to get arrested. “We’ve come to realize that we often persuade more people by being friendly than by being hostile,” he told the Washington Post.

The data-driven approach appealed to other groups. In 2004, Wayne Pacelle took over as CEO of the Humane Society of the United States—an animal-welfare behemoth with a $200 million annual budget—and announced his plan to do more work on behalf of farm animals. Among his first decisions was to bring in Paul Shapiro so he could run the new campaign.

The Humane League, a grassroots group founded in 2005 that was similarly instrumental in the cage-free campaign, also pushed the utilitarian mindset. The organization’s website says its leaders aim to use “the head to balance our heart for the greatest impact for animals.” In practice that means assessing possible campaigns according to the number of animals affected, the severity of those animals’ suffering, and the likelihood of meaningful success. When they considered all these factors, they came to the same conclusion as Shapiro: Their time and money would best be spent on chicken welfare. “For us the battery-cage issue is at the perfect intersection of these metrics,” says executive director David Coman-Hidy.

Coman-Hidy’s group even has a research arm, Humane League Labs, under the leadership of a network scientist and animal-loving numbers nerd named Harish Sethu. The lab will test the effectiveness of different outreach efforts to reduce our meat consumption, using preregistered experimental designs and careful data analysis. At the Humane League Labs blog, Sethu has already posted sophisticated mini-essays on methodological questions such as the dangers of using p-values and the importance of statistical power.

The emergence in the animal-welfare community of what Shapiro calls “strategic pragmatism” and Coman-Hidy describes as “outcome-based thinking” dovetailed with a broader trend in do-gooder-ism. The “Effective Altruism” movement, so named by philosopher Will MacAskill in 2011, has tried to make charitable behavior more rational and quantitative: If I want to give away my money, its proponents ask, then what’s the best return that I can get? Which causes will be most cost-effective? For example, which would save more children’s lives in the developing world—paying for their vaccinations or spending the same amount on mosquito nets?

In his 2015 book, Doing Good Better: How Effective Altruism Can Help You Make a Difference, MacAskill applied such thinking to the effects of reducing one’s carnivory. The average American’s diet results in the death of 0.1 cows per year, he wrote, along with 0.4 pigs, 0.8 turkeys, 0.8 egg-laying hens, and 28.5 broiler chickens. To be a little more exact, he continued, one might consider the total number of “animal years” lost to eating meat, as opposed to the number of animal lives. For example, since broiler chickens tend to live for only six weeks each, the total cost of eating them is more like 28.5 (chickens per year) times 0.115 (years per chicken), or 3.3 chicken-years in all. When he did the same math for other animals, he arrived at lower numbers—0.3 turkey years, 0.2 pig years, and 0.1 cattle years. Thus he reasoned that by far the most efficient dietary change, in terms of helping animals, would be to give up chicken first.

Would anyone really take this advice to heart? I’ve met lots of people who, for the sake of their health or conscience, eat chicken and avoid red meat. I’ve met none at all who do the opposite. The Effective Altruist might see this as a flaw of reasoning, if not a major source of waste in our efforts to improve the world.

In fact, they might view the animal-welfare movement as a whole as being riddled with such mistakes and inefficiencies—and thus well-suited to rational, utilitarian reform. Of all the charitable donations in the United States, says Jon Bockman, executive director of an Effective Altruist organization called Animal Charity Evaluators, just 3 percent of all charitable donations in the U.S. go to animal-welfare and environmental groups. From the tiny slice that goes to helping animals, he says, just 1 percent gets slivered off into work on factory farming. Indeed, Bockman argues that the most cost-effective human-based charities return one spared life per several thousand dollars spent—while the equivalent donation to a well-run animal charity could save tens of thousands of animal lives. “We think that’s a more valuable proposition,” Bockman told me. He thinks helping chickens represents a triple-bargain: If animals are hugely undervalued as compared with humans, then farm animals are hugely undervalued as compared with dogs and cats, and birds are undervalued as compared with cows and pigs.

As Bockman talked me through this compelling math of misery, a dark thought came into my mind. As a rule of thumb, his reasoning implied, it’s more efficient to save smaller animals than bigger ones, since more of them must die to make the same amount of meat. Seen the other way around, it would be more efficient—and much better for the animals—if we only ate the biggest species we could find. I took this one step further. Why not domesticate the elephant and raise it as a source of food? If we switched our poultry farms to pachyderms, we’d have reduced the deaths associated with our diets by a factor of 500.

That doesn’t sound so good to me, because I’m what Jon Bockman might call a “species-ist.” I think elephants—sweet, sensitive, and social creatures that they are—should count for more than chickens do. I think their suffering should receive a higher value in the cosmic calculus. In other words, I’d rather that we all ate lots of little birds. So would most Americans, I suspect. (Bockman, of course, would rather we eat no meat at all.)

The strategic pragmatists might see my preference for certain kinds of animals as both a moral failing and a source of waste—a way in which the heart overpowers the head and hides the greatest suffering. In fact, a fervent anti-species-ism forms the very basis of their project. Why have animal charities put so much time and money into worthy but marginal causes such as sheltering dogs and cats, fighting fur, and pulling chimpanzees out of research labs? Because their donors and their members are benighted by an anti-pig, anti-cow, anti-chicken bigotry.

In one sense, the cage-free campaign reflects devotion to the data—with animal-welfare groups reallocating time and money in accordance with tallied deaths and measured pain. But in another sense, the change in focus has had less to do with analytics than with fundamental values. The calculations only make the activists’ underlying values clear: Chicken-pain matters just as much as kitten-pain; the animals are equal in their suffering. This broadening of the moral circle, first into the pastures and the barns and then into the wire cages, led the shift to poultry rights.

If one happened to be starting with a different set of values—one that didn’t cotton to the chicken-pig equivalence, perhaps—then the same sort of mathematics could yield a different, just as rational conclusion. Take all those people who give up red meat and still eat fish and chicken. Who’s to say they haven’t done their own private, moral computation, with a chicken’s pain set equal to a tiny fraction of a pig’s?

In any case, the outcome-minded activists have their next step figured out. Both Shapiro and Coman-Hidy say their groups will move toward helping broiler birds, which compose the large majority of slaughtered chickens. After chickens, maybe fish. In aquaculture, no one keeps track of individual animals: The fish are measured by the pound. But Coman-Hidy says the piscine death and suffering may be an order of magnitude higher than that of land animals. “It’s in the billions,” Shapiro told me. “The fish are overcrowded and kept in squalid conditions; they suffer from parasites, and the waters are dosed with antibiotics and other drugs.” (Do fish feel pain? Some scientists say they do. Others say they don’t. There seems to be some doubt.)

Even fish could be seen as a distraction. Harish Sethu, the head of the Humane League Labs, has noted that 40 billion shrimp are killed for food per year—that’s nearly five times as many shellfish deaths as chicken deaths. Would action on behalf of shrimp be five times more effective?

Jon Bockman’s Animal Charity Evaluators doesn’t shrink from any plausible conclusions. “We’re very concerned about wild-animal suffering,” he told me, expanding on his organization’s “firmly antispeciesist stance.” “As we do more research, we realize there are so many species that reproduce successfully by producing hundreds or thousands of offspring, and 99 percent of those newborns either starve or succumb to some sort of painful death.” The number of animals that die this way—wild rabbits, fish, frogs, etc.—dwarfs the number that die on farms. “Our current estimate is 10 trillion,” Bockman said.

I wasn’t sure that I understood what he was saying. Was he suggesting that we intervene to help, say, all the excess tadpoles in a pond—natural victims of an evolved reproductive strategy? What if saving all the tadpoles caused some other creature pain? Wouldn’t it be dangerous to privilege the pain of these individuals over the broader health of the environment?

“These are really complex questions,” said Bockman. “We don’t have a good idea of how to combat this without upsetting the ecosystem, and it’s controversial because the public thinks it’s natural and we’re supposed to leave that as it is.” That’s why the issue of saving wild animals has only come up a few times at Animal Charity Evaluators. They’re also careful in discussions of insect welfare, since it isn’t clear, scientifically, how much an insect suffers. (If each one felt even just a tiny, tiny bit of pain, their sum-total suffering could still be astronomical.) “We’re very mindful of the fact that we don’t want to make our organization seem more radical.”

That’s the thing about the numbers-based approach to helping animals: It seems reasonable and rational up until the moment when it sounds totally insane. In practice, though, no one has plans to raise money for a save-the-wild-tadpole campaign. In keeping with their own philosophy, the strategic pragmatists always try to be pragmatic. They focus on those issues where they think they have the greatest chance of making progress—and for now that means doing what they can to nudge the movement toward neglected animals on farms. “I don’t think that all resources in the entire world should be focused on this,” Coman-Hidy told me. “We’re at a point now, though, where such a vanishingly small number of resources are being used to help farm animals, that I’m more interested in shifting things over.”