Last winter, William MacAskill and his wife Amanda moved into a Union Square apartment that I was sharing with several friends in New York. At first, I knew nothing about Will except what I could glean from some brief encounters, like his shaggy blond hair and the approximation of a beard. He was extremely polite and devastatingly Scottish, trilling his “R”s so that in certain words, like crook or the name Brooke, the second consonant would vibrate with the clarity of a tiny engine.

MacAskill, I soon discovered, was a Cambridge-and Oxford-trained philosopher, and a steward of what’s known as effective altruism, a burgeoning movement that has been called "generosity for nerds." Effective altruism seeks to maximize the good from one's charitable donations and even from one’s career. It is munificence matched with math, or, as he once described it to me memorably, “injecting science into the sentimental issue of doing good in the world.”

Up to that point, I would have described my interest in charity as approximately average. I certainly hadn’t thought deeply about my donations long before I met MacAskill. I'd volunteered for music-education programs because I liked music, but this felt not like an exercise in selflessness, but rather an expression of my personal identity, like wearing clothes.

One night at an apartment party, MacAskill and I huddled with some beers in the corner of the kitchen to talk about his worldview, which he was turning into a book called Doing Good Better (out July 28.) Imagine you are a thoughtful 22-year-old college graduate who wants to make a great difference in the world, he said, invoking one of his many thought experiments. Many such people try to get a job with Oxfam, the Gates Foundation, or any number of excellent charities. That's fine. But if you don’t get that job at Oxfam, somebody just as smart and generous will get it instead. You’re probably not much better than that “next person up.” But imagine you go to work on Wall Street…

Wall Street? I probably interrupted.

Yes, imagine you work in investment banking. You make $100,000 and give away half to charity. The “next person up” would not have done the same, so you have created $50,000 of good that wouldn’t have otherwise existed. Even better, your donation could pay for one or two workers at Oxfam—or any effective cause you chose to donate to.

This story underlines an effective-altruist principle called “earning to give,” which is like tithing on steroids. Earning to give argues for maximizing the amount of money you can make and donating a large share of it to charity. What attracted me to the story wasn’t the specific advice (I have not yet sent a resume to Wall Street) but rather the philosophical approach to pursuing good in the world—counterintuitive, and yet deeply moral and logical. It was like pinpointing a secret corpus callosum connecting the right-brain interest in being a good person with a left-brain inclination to think dispassionately about goodness.

I. A Reason to Give

Will MacAskill was a source of compelling answers at a time when I was in need of new ways to make sense of life’s chaos. Six months before I met Will, my mom died of pancreatic cancer. Several months after I met Will, my dad was admitted to Georgetown University hospital with what doctors would later determine was a different and freakishly rare cancer that had wrapped like ivy around the vertebrae of his lower back. When he was admitted to the hospital for lower back pain, the surgeon initially anticipated that  all that was required was a straightforward surgery. After my father nearly bled out on the table after the first of several operations, doctors realized that my dad was dealing with a large malignant tumor.

I spent each day for several weeks last summer making a home in the waiting room of the hospital's spinal-injury unit. Every hospital waiting room is an antiseptic purgatory—one in which "Family Feud” plays for an eternity—and in the surreal déjà vu of possibly losing another parent to another cancer just a year apart, I thought about a lot of things, like luck, religion, and goodness. My mom passed away when she was 63; my dad was still in his 60s. A feeling solidified behind the grief: revulsion at the prospect of coming into my parent's retirement money. Something else was clear to me, too. Should that unspeakable scenario come to pass, I promised myself, I would reach out to Will and ask him to help me to give away the money—and not just anywhere, but to to the cause that would improve the lives of others by as much as possible.

My dad’s cancer blessedly went into remission, and he is now in recovery. But the instinct to give away a meaningful amount of money didn't leave me. I can’t say for sure why I latched onto this notion so strongly. Maybe I was ashamed to have come so close to doing something unequivocally good only to have pulled back because my dad’s recovery had intervened; being thankful seemed like a bad reason to withhold an act of generosity. Maybe I wanted to add a chip of life to the cosmic scales, which had lately leaned too far to the other side. Maybe this donation was the equivalent of an agnostic’s prayer, on the off-chance the supernatural accepts gifts in the form of altruism, to simply make the bad things stop. The truth is that I don't know why I decided to do what I’m doing, and therefore feel no reason to tell other people that they should do anything similar. I’ve never liked a sermon.

That my motivations are both myriad and obscure to me isn't so strange. Altruism, which derives from the Italian word altrui for "other people,” once mystified biologists. Selflessness stumped early advocates of natural selection (giving food to starving rival tribes is likely a bad way to ensure the survival of your own) and inverts Adam Smith’s metaphor of the invisible hand, which suggests that individuals’ pursuit of self-interest can be beneficial at scale.

As Sam Kean explained in The Atlantic article “The Man Who Couldn't Stop Giving,”  the mainstream theory of altruism’s roots is known as “kin selection.” Since the engine of evolution is procreation, any gene pool should be rewarded for the instinct to help relatives (including distant relatives) survive and pass along their genes—even when that assistance requires great sacrifice. Altruism, in this interpretation, is natural rather than super-human. Ants, bees, and many other species show clear signs of altruism. Slime molds in the canopies of trees sacrifice themselves to strengthen the group. Even the most generous among us are chasing the self-sacrificial instincts of mold.

But it was important to me that the donation meet a higher standard. I was interested, both emotionally and intellectually, in a larger question: What is the best charitable cause in the world, and would it be crazy to think I could find it?

II. The Scientific Method of Goodness: Effective Altruism

There are so many causes that focus on improving lives, and the spectrum is vast. Some worthy programs save lives (e.g. drug research to avert premature death), others alleviate suffering and poverty (e.g. by providing irrigation), and others focus on enrichment (e.g. by giving to a museum).

These programs exist along another wide spectrum, which is certainty. Some organizations distribute proven drugs (quite certain), others develop unproven drugs (less certain), and some lobby to reduce global carbon emissions (more uncertain). The point isn’t that the certain causes are better than less-certain causes, but rather that thoughtful donors weigh the risk that their donations won’t pay off, as they would any other investment.

When I decided that I wanted effective altruism to guide my decision, I called Will again to get a better understanding of the philosophy I was wading into. Then I spoke with several poverty experts and moral philosophers to learn why the movement might be misguided. I wanted to know it deeply, to see it closely, its virtues and its flaws.

The simplest way to explain effective altruism and its discontents is to begin with three pillars of the movement: (1) You can make a truly enormous difference in the world if you live in a rich country; (2) you can "do good better" by thinking scientifically rather than sentimentally; and (3) you can do good even better by trying to find the greatest need for the next marginal dollar.

1. The Wealth of the 1 Percent

Even middle-class American families are rich compared to the world’s poor. “If you earn more than $52,000 per year, then, speaking globally, you are the 1 percent,” MacAskill writes. Some research suggests that the doubling one's income, whether you make $500 a year or $50,000 a year, roughly raises one’s happiness by a similar amount. This implies that if a middle-class American family were to transfer one percent of its income directly to an Indian rice farmer, his estimated happiness would double.

In his book, MacAskill calls this the 100x Multiplier: Donations to the world’s poorest are an unalloyed mitzvah and, if you are left-brain inclined, a mitzvah on extreme discount—a 99-percent-off sale for well-being in the world.

This line of thinking is morally powerful, and its radical implication is that one should devote every spare dollar and every spare moment to helping the world’s poor—eschewing the arts and exercise, banning oneself from all entertainment, subsisting on rice, and giving away all of one's possessions. The moral philosopher Peter Singer once proposed a famous thought experiment: You see a child drowning in a pond. Do you jump in after her? Even if you didn’t push her in? Even if you’re wearing an expensive suit or dress? The socially acceptable answer to the question is you ruin your suit to save the child. But ordinary people with plentiful savings justify ignoring the deaths of children every day, even when the opportunity to save them is as close as an Internet connection.

Some rationalists flirt with extreme levels of selflessness, but I am not seduced by that sort of misery. MacAskill emphatically says that he’s not trying to heal suffering in the developing world by advocating for suffering in the developed world. The organization he co-founded is called Giving What We Can, not Giving All We Have, and it does not argue for the abolition of cake, art, or whiskey. Effective altruism is not a plot to guilt the rich into asceticism.

"You should spend a good amount of your money trying to make the world as good a place as possible,” said MacAskill, whose non-profit 80,000 Hours offers research and advice for seeking the most meaningful careers. “But you shouldn’t beat yourself up for not donating all your money.” The feasible alternative for most people, he said, is to give a little bit more than they already do—and to focus their donations on scientifically proven outcomes.

2. The Scientific Method for Being Good

Perhaps the most piercing lesson from effective altruism is that one can make an astonishing difference in the world with a pinch of logic and dash of math.

In his book, MacAskill tells the story of two academics, Michael Kremer and Rachel Glennerster, whose randomized controlled trials in Africa found that neither textbooks, flip charts, nor smaller class sizes raised the test scores of students in Kenya. Kremer did find, however, that every $100 spent treating intestinal worms in children dramatically raised their school attendance. On the basis of this research, Kremer and Glennerster cofounded the Deworm the World Initiative, which helps developing countries launch and run their own deworming programs. Today, Deworm the World is widely considered one of the most cost-effective charities in the world.

But programs like Deworm the World don't receive the lion's share of U.S. charity. Of the $330 billion that American individuals, companies, and foundations give to charity, just 5 percent goes directly overseas. That means if Americans shifted just 5 percent of their remaining charity abroad, foreign donations would double; if the money were spent twice as efficiently (a low bar, according to MacAskill), the number of lives saved and improved would quadruple—and that’s without Americans giving an extra cent to charity.

Critics of effective altruism argue that if you’re trying to scientifically maximize the greatest good, there is a risk of privileging the causes that are most easily quantifiable. The value of deworming might be measurable, but what of the values of women’s rights, equality, or democracy? Imagine the impossibility of designing a randomized controlled trial to determine the value of a free press in the United States. One would ideally have access to a cosmic multiverse: Compare the universe where America has a free press with a universe where America is the exact same, except it doesn’t have a free press, run that experiment over and over again, and then calculate the resulting differences in national incomes, happiness, and equality. Even Elon Musk and Peter Thiel aren’t going to fund that.

International advocacy is another fine example of a hard-to-quantify good. For example, if activists had persuaded Western governments to remove the patent on antiretroviral drugs for HIV and AIDS in the 1990s, millions of deaths in the developing world might have been averted. But how do you run a randomized controlled trial to study the value of a lobbying effort? Effective altruists like MacAskill would respond that even these risky undertakings can be boiled down to math problems: If you build an equation that multiplies the greatest number of possible lives saved by the odds of that program’s success, you can estimate the highest expected value of your donation. But overall, effective altruism seems to focus its attention on the most measurable interventions.

3. The “Next-Dollar” Test

A few weeks ago, hedge-fund manager John Paulson pledged $400 million to Harvard University's School of Engineering and Applied Sciences, the largest private donation in Harvard’s history. A month earlier, Blackstone Group CEO Stephen Schwarzman announced a $150 million donation to Yale University to build a cultural center. Harvard and Yale's combined endowments are more than $50 billion and growing by billions annually. "It came down to helping the poor or giving the world's richest university $400 [million] it doesn't need,” Malcolm Gladwell wrote sarcastically on Twitter. "If billionaires don't step up, Harvard will soon be down to its last $30 billion.” Many people countered that Harvard is a singular fount of engineering research and technology.

But, as Vox’s Dylan Matthews (who is, overall, one of the media’s smartest commentators on effective altruism) pointed out, this counter-argument failed a certain “next-dollar” test. Harvard already has a $20 billion endowment and one of its science and engineering buildings is named after Mary Maxwell Gates and Beatrice Dworkin Ballmer—the mothers of former Microsoft CEOs Bill Gates and Steve Ballmer—whose families have collectively given almost $100 million. "This is what philanthropists like to call a ‘crowded' funding space,” Matthews wrote. "It’s wasteful to make crowded spaces even more crowded.”

In other words, the wisest question is not  “What is the greatest good?” but rather “What is the greatest good where the next dollar could have the greatest impact?"

Effective altruists often criticize disaster relief for failing to meet this test—not because earthquakes and tsunamis aren’t horrible, but because their bloated responses often eclipse other needs. In the aftermath of the Haiti earthquake, the Red Cross continued asking for money "well after it had enough for the emergency relief that is the group’s stock in trade,” ProPublica reported in a June expose accusing the Red Cross of building just six permanent homes after raising half a billion dollars. Not all aid groups followed suit, they said: "Doctors Without Borders, in contrast, stopped fundraising off the earthquake after it decided it had enough money.”

III. The Measuring of Life: GiveWell

When I asked several philosophers and poverty experts what causes they would give to, answers ranged from women’s rights to direct transfers to the poor. Iason Gabriel, a politics lecturer at Oxford University, made a surprisingly strong case for tax reform in the developing world. Africa, he said, loses tens of billions of dollars a year in illicit flows of money, even more than it receives in government aid. Helping governments crack down on tax avoidance could preserve billions in funds for the state to direct toward health and education. But I felt drawn to two personal values for my donation: I wanted to prevent premature deaths, and I wanted a high degree of scientific certainty that the money would be spent well.

The most common refrain from experts I consulted was that my priorities pointed in a clear direction: If what you want is to save lives with certainty, several people said, you have to go to GiveWell.

In 2006, Holden Karnofsky and Elie Hassenfeld were young Ivy-league-educated workers at a hedge fund, making more money than they needed, and searching for a worthy charitable cause. “We wanted the biggest bang for our buck,” Hassenfeld said, and since few outside organizations offered much guidance, they formed a club of several like-minded people to research a simple question: How did various charities spend money, and was there any evidence that they were doing good? “We were calling charities directly, but we weren’t always getting good answers,” he said. The gaping lack of hard data, combined with their personal mission to find that elusive greatest cause, inspired them to create GiveWell in 2007.

GiveWell is a meta-charity, an organization that evaluates other charities. They have four broad criteria, in Hassenfeld’s words: “effectiveness” (does the charity make a difference?), “cost-effectiveness” (how much difference does the charity make per dollar received?), “room for funding” (can the charity use your donation in the near future?), and “transparency” (is the charity forthcoming about its spending and its results?). Its top-ranked charities for this year include GiveDirectly, a radically simple approach to sending no-strings-attached cash to extremely poor households, and the Against Malaria Foundation, which distributes insecticide-treated malaria nets in sub-Saharan Africa. It’s impossible not to be struck by the encyclopedic thoughtfulness of GiveWell's analyses, which take months to complete and are often thousands of words long, contain more than 100 footnotes, and elaborate on concerns they have for even the top-ranked charities.

It is hard for the casual donor to determine on her own which charities do the most good. For example, compare two well-meaning organizations: Charity A accepts $100 and sends $90 to the field to buy better textbooks for Kenyan children. Charity B accepts $100 and sends $45 to the field to buy deworming tablets for Kenyan kids. If you focus on “overhead" costs, as many people do, the choice is clear: Charity A is twice as effective. But randomized controlled trials have shown that while textbooks do little to raise school attendance, medicine for intestinal worms often helps children go back to school. In the end, Charity B might be many times more effective. This is why it’s so important for organizations like GiveWell to track dollars and outcomes.

But comparing outcomes is tricky. Is it better to avert a death from a tropical disease, or to raise a family from abject poverty? Philosophically, the most difficult task facing GiveWell is putting the vast spectrum of human suffering into numbers. It is, in a way, a math problem, but one laden with value judgments, about which reasonable people can disagree.

For example, to compare suffering across countries, some organizations use a metric called DALYs, or Disability-Adjusted Life-Years. One DALY could equal one year lost to early death, 1.67 years of blindness, or 41.67 years suffering stomach pain from an intestinal parasite. If a program has averted 80 DALYs, it might have saved the death of one infant or cured minor health problems for several adults.

To choose the charity that represented the greatest good as I saw it, I had to choose my values. Disability-Adjusted Life-Years acknowledge no difference between averting fewer deaths and improving many lives, but because my donation had been forged by death and near-death experiences, I was motivated to err on the side of saving lives rather than simply improving them. And because this represented my first major donation, I wanted to donate to a cause whose impact was certain.

It is not obvious to effective altruists that certainty is the right way to think about doing good. Imagine, for example, if you face a 1 percent chance of saving a million lives versus a 100 percent chance of saving ten lives. The certainty thesis might lead one to choose to save the single life. But the expected value of the first option is 10,000 lives saved—a 1,000 times difference in outcomes.

Still, when I expressed my values to Hassenfeld, he had a very specific recommendation. "I think the Against Malaria Foundation is the right choice for you,” he said. “That’s where I gave half of my donations last year, and if I had your values, it’s where I would give now.” That left a final step: calling the founder of the Against Malaria Foundation and learning more about the charity GiveWell has rated the number-one in the world.

IV. The Cause: Against Malaria Foundation

The next morning, I called Robert Mather, the British founder of the Against Malaria Foundation, to find out how a businessman with practically no NGO experience came to run one of the most effective charities in the world. He told me his life was abruptly changed due to a freak fire involving a family of strangers 40 miles outside of London.

"I’m rubbish with a TV remote control, and that led to a major left turn in my life,” he began. "I was trying to turn off the BBC in 2003, and instead, I pressed a button that went to another channel. It was a documentary featuring a child who seemed to have melted in a fire.” The child was Terri Calvesbert, a one-year-old girl living in Suffolk, England, who lost 90 percent of her skin, including her nose and eyelids, in a fire sparked by her mother's discarded cigarette. Calvesbert was burned so badly that when firefighters found her, they initially mistook her for a burned doll. "She had been put into an artificial skin body suit,” Mather recalls. "I’m not an emotional person, but my wife and I had two children, and I am not ashamed to say that I was streaming.”

Six months prior, Mather had participated in a charity bicycle ride, and it occurred to him that he could organize a similar event to raise money for the girl. Mather called swimming-event organizers in Sydney, New York, Lima, and elsewhere. His effort resulted in 150 coordinated global swims, with thousands of participants raising hundreds of thousands of dollars for Calvesbert, who is now 18 years old.

The global success of “Swim for Terri” sent Mather’s cogs whirring. If one girl could inspire $400,000 in donations, what could a truly international cause do? “As you scratch beneath the surface on global health issues, the same disease comes up as the biggest killer of kids in the world and biggest killer of pregnant women,” he said. “Malaria was a no-brainer.”

Approximately 200 million people suffer from malaria each year, and the death estimates range between 400,000 and 800,000. About 90 percent of those mortalities are in sub-Saharan Africa, and three-quarters of them occur in children younger than five. The second-order effects of the disease are vicious: Malaria is a massive impediment to economic growth, since survivors often cannot work, and parents have to devote their lives to caring for their sick children.

I’ve read, and typed, and read again these numbers, and they are so stark to me that they can easily float away into the atmosphere of statistics, escaping true empathy. Understanding one nation’s experience feels more visceral: Every day, more than 500 people die from malaria in the Democratic Republic of Congo, and the majority of these deaths are children under the age of five. AMF offers a shattering metaphor: Imagine a fully booked 747 airplane and infants strapped into seats A through K of every row of the economy section; their feet cannot reach the floor. Every day, this plane disappears into the Congo River, killing every soul on board. That is malaria—in one country. By GiveWell’s calculations it would cost $1.7 million to save the airplane.

While larger fish like the the Global Fund and the Gates Foundation focus their resources on developing a fast and absolute cure, AMF has a preventative approach: cheap insecticide-treated bed nets (about $7.50 in the DRC) that block and kill the mosquitoes that carry the disease from person to person.

There are four reasons why AMF is currently the top-rated charity at GiveWell. "First and foremost, giving out nets to prevent malaria has among the best evidence of any program that charity dollars can support worldwide, and more than 20 randomized controlled trials show it works,” Hassenfeld said. "Second it’s really cost-effective, at about $3,500 dollars per life saved. Third, AMF itself has significantly more room for funding. Finally, AMF has a strong and unique commitment to transparency and monitoring.” Mather’s approach is like the platonic ideal of effective altruism, matching a clear-eyed approach to doing good with scientific exactitude, using smartphone technology to track the delivering and implementation of every net he distributes. "We’ve distributed 700,000 nets with smartphone technology,” he said. “We know within six meters where all 700,000 nets are.”

V. Greatest Good

In his new book The Most Good You Can Do: How Effective Altruism is Changing Ideas about Living Ethically, the moral philosopher Peter Singer laments the fact that most people are more motivated to give by stories rather than numbers. For example, people are more likely to donate when they see the photo of one child rather than see several children suffering from the same disease. In my experience, I have found the exact same thing: Individual stories motivate, and statistics overwhelm.

Why do people mute their emotions in the face of greater suffering? A study from Keith Payne at the University of North Carolina found that "the collapse of compassion happens because when people see multiple victims, it is a signal that they ought to rein in their emotions [because] the alternative might seem too difficult.” It is a frustrating, yet nearly poetic, idea: The problem is not a lack of empathy, but the fear of feeling too much.

Some people in the past few weeks suggested to me that effective altruism suffers from a “cyborg problem.” That is, if you talk about human suffering like it’s a calculus equation, the empathic brain will shut down. But GiveWell has found the opposite to be true. “A large contingent of donors tell us they give more than they would have, had GiveWell not existed," Hassenfeld said. “We’re asking questions that encourage people to give, because we give them confidence that they can make a difference.” Even as I’ve sought to find the holes in the philosophy I’ve chosen to adopt, I’ve become more convinced by effective altruism’s potential for widespread popularity. The mathematical challenge of finding the greatest good can expand the heart. Empathy opens the mind to suffering, and math keeps it open.

In the end, I considered making several different donations. But I kept coming back to something Robert Mather said: Malaria is not merely the greatest killer of children in the world, but also it is the greatest killer of pregnant women. The disease plunders motherhood from both sides of the equation. The loss of a mother must be quantifiable by some measure of creative accounting, but in my experience it is immeasurable. This much I knew: There is the thing that I want, I cannot have it, but I can give it to somebody else. That seemed to honor the etymology and the root of altruism.

On Thursday, I wired the money: a thousand for every year of life for my mom, who died a few months before her birthday. To honor a family tradition, I also sent an extra thousand to GiveWell—"to grow on,” she would have said.