Cari Tuna and her husband committed in their 20s to the Giving Pledge, the campaign started by Bill Gates and Warren Buffet to encourage billionaires to donate most of their wealth. (Lettering by Joel Holland for The Washington Post/Photo by Marvin Joseph/The Washington Post)

When Cari Tuna and her future husband, Dustin Moskovitz, a Facebook co-founder, decided they would give away most of their multibillion-dollar fortune to charity, they thought of asteroids.

Or more specifically, the risk of one slamming to Earth and causing mass destruction.

It was one of many early ideas and it wasn’t that they had any special passion for or expertise in the subject, but it wasn’t a joke either. In trying to figure out how they could make the maximum impact with their money, the couple wanted to cast as wide a net as possible and systematically evaluate every cause on its merits.

No matter how wacky or intractable a problem may seem at first glance.

“We wanted to include anything that could seriously derail humanity’s progress,” Tuna explained in a recent interview. “It’s a pretty scary list.”

Tuna and Moskovitz were in their mid-20s in 2010 when they became the youngest couple ever to sign on to the Giving Pledge, the campaign started by Bill Gates and Warren E. Buffett to encourage the world’s billionaires to commit to giving away most of their wealth.

They had little experience with philanthropy, but they believed that the bulk of the money Moskovitz had made — estimated to be $8.1 billion by Forbes — should be returned to society in their lifetimes.

The question was how.

With Moskovitz working crazy hours at his new start-up, Asana, a collaboration and messaging company, the primary responsibility for figuring out how to give away the money fell to Tuna.

Their Silicon Valley peers had advice. What Tuna heard the most was to pick a worthy cause she believed in such as poverty, education or oceanography and go from there. Others recommended she look into problems that affected her personally.

They noted the splash Mark Zuckerberg and his wife, Priscilla Chan, made in 2010 with their $100 million donation to the Newark school system. And they pointed to the advances Google co-founder Sergey Brin, who has a gene that puts him at higher risk for Parkinson’s, has brought to the field with $150 million in donations.

But those approaches didn’t quite resonate with Tuna.

Tuna and Moskovitz, who is pictured here, were in their mid-20s in 2010 when they became the youngest couple ever to sign on to the Giving Pledge. (Araya Diaz/Getty Images for TechCrunch)

What she wanted to do was the most good they could in any area — which sounded simple enough but turned out to be incredibly difficult to execute.

“The conventional wisdom is to say, ‘What am I passionate about?’ and go for something in that area,” Tuna said. “That can be a great way to do things, but at the same time, I think that by just going with that, you’re leaving a lot of opportunity for impact on the table.”

She points to iodine deficiency, which has been linked with low IQs in children in the developing world. It’s “not a super-sexy topic,” she says, but its remedy can have a major impact on a community and can be in­cred­ibly cheap and easy to implement.

As Tuna and Moskovitz, now 29 and 30, respectively, began to compare one possibility with another and then another, they have become pioneers in an emerging philosophy of philanthropy known as “effective altruism” — which applies evidence and reason over things like emotion and intuition to determine where one can do the most good.

The duo are emblematic of a new generation of millennial philanthropists seeking to give far beyond their own communities and experiences.

Americans have traditionally focused their donations on organizations such as schools, churches and cultural centers close to home. But with the rise of social networks that connect people the world over instantaneously, many millennials have a broader view of charity.

After three years, several hundred interviews and trips that took them from Washington think tanks such as the Brookings Institution to health clinics in Burma and rural villages in Kenya, they have narrowed their interests to four major “buckets”: U.S. policy, global catastrophic risks, international aid and science. They plan to announce their first major focus areas in early 2015 and eventually hope to scale up to give away hundreds of millions of dollars a year. Tuna said she is excited to get started.

“I came to this work without a really fixed worldview as most philanthropists do that are coming to this after highly successful careers in other fields,” said Tuna, who serves as president of Good Ventures, the couple’s foundation. “I have a blank slate, and I’m trying to use that as an advantage.”

A blind date

When Tuna first heard the name Dustin Moskovitz in 2009, she was fresh out of Yale and a newbie reporter in the Wall Street Journal’s San Francisco bureau. A co-worker of hers knew him from college and thought they would hit it off, so she set them up on a blind date.

The friend was right.

Moskovitz, one of Zuckerberg’s Harvard roommates, had moved out West to become Facebook’s third employee and chief technology officer. It was clear from the get-go that he and Tuna shared a similar worldview. They were both modest, direct and cared immensely about being good and doing good.

Raised in Evansville, Ind., Tuna was the eldest of three children born to two doctors. In high school, she was valedictorian (“co-valedictorian,” she corrects), student council president (she notes that she ran unopposed) and founded her school’s Amnesty International chapter (it was a small school, she says). At Yale, she studied political science and spent much of her time at the college paper. She did some writing for her home-town paper, the Evansville Courier & Press, and interned at the Minneapolis Star Tribune. She spoke some Arabic and Turkish and thought that maybe she’d like to be a foreign correspondent one day.

Moskovitz grew up in a small city in inland Florida that’s best known as a place where several major highways pass through. His dad was a psychiatrist and his mother was a teacher and artist. As a boy, he dreamed of being an air force pilot, but at Harvard he studied economics and decided business was his future.

That famed Facebook IPO was still a few years away when they met, and Tuna said it wasn’t until a few dates into the relationship that it dawned on her that the guy she was seeing was likely to become very wealthy.

“I knew he was a co-founder of Facebook and I used Facebook,” she said, “but I had just moved out to San Francisco and wasn’t really all that familiar with the tech world. It was pretty shocking.”

In 2011, when Moskovitz was 27, Forbes named him the world’s youngest self-made billionaire. That same year, Tuna quit her job at the Journal to work on the couple’s charitable giving full-time. They weren’t even engaged, but even then Moskovitz talked about Tuna as his “partner” in life, and his public comments about the future often included her.

“Cari and I are stewards of this capital,” Moskovitz wrote in a Quora chat in 2013 shortly before they married. In response to a question about what it feels like to be a billionaire, he said: “It’s pooled up around us right now, but it belongs to the world. We intend not to have much left when we die.”

Today, Tuna and Moskovitz have a reputation for being among Silicon Valley’s most low-key billionaires. Friends and colleagues mention that they prefer to spend their free time doing yoga, meditating and taking walks. They fly coach, share a used car and bike or take public transportation to work.

Paul Brest, a Stanford law professor who is the former head of the William and Flora Hewlett Foundation, said their unassuming lifestyle translates to their approach to philanthropy.

“There’s nothing wrong with naming a foundation after yourself, but I think it’s indicative about their thinking about philanthropy that they named theirs Good Ventures,” Brest said. “It highlights how the outcomes matter more than themselves.”

Over the past three years, Tuna and Moskovitz have quietly given away 61 grants worth nearly $45 million through their foundation. (This is Tuna’s first major interview.)

“Old souls,” is how Laura Arrillaga-Andreessen, a personal friend and mentor, describes the couple.

She said Tuna herself is “deeply spiritual and has an immense sense of responsibility” for the task she has been given. Arrillaga-Andreessen, wife of Netscape founder Marc Andreessen and who teaches courses at Stanford about philanthropy, has advised numerous tech billionaires — including Tuna and Moskovitz — about their charitable work.

Arrillaga-Andreessen said Tuna’s leadership of the couple’s foundation leverages the “seriousness, due diligence, investigation, level of public transparency and integrity” that Tuna embraced in her journalism.

Tuna herself sometimes wonders if she’s a little too cautious.

“Dustin has more of a natural appetite for risk than I do,” she said, adding that “For me feeling like a steward of the resources sometimes makes me feel a little risk averse, and I have to consciously work against that.”

The lives you can save

Early in her research, Tuna came across Peter Singer’s “The Life You Can Save” — a book she cites as the catalyst for their approach. An Australian philosopher, Singer makes the moral case for giving, arguing that many people in the developed world can do so at little cost to themselves.

Tuna and Moskovitz soon found a kindred spirit in a Harvard grad named Holden Karnofsky, now 33, whom they met through a mutual friend.

A former hedge fund analyst, Karnofsky was frustrated that he could not compare the impact of different charities when he tried to give away $5,000 of his own one year. So he and a colleague, Elie Hassenfeld, quit their jobs and founded an independent, nonprofit charity evaluator that they dubbed GiveWell.

“There is an infinite amount to do and very little philanthropy, so how do you make good choices?” Karnofsky said.

Tuna and Karnofsky approached the challenge like reporter-scientists, partnering to collect data on the universe of possible causes, evaluate them and share their findings online for anyone interested to see. As part of a joint venture between Good Ventures and GiveWell that they called the Open Philanthropy Project, they talked to foundation heads, technical experts, historians, biologists, former government officials, political campaign managers and many others.

In face-to-face meetings, Tuna has a reputation for being a persistent and tough interviewer.

“She exhibits a very healthy skepticism,” said Susan Urahn, executive vice president at Pew Charitable Trusts who has met with Tuna several times. “She takes nothing at face value.”

Karnofsky said that Tuna prioritizes “honesty and directness.” “I think she’s often frustrated by people in the nonprofit world who are overly positive, prone to flattery and hesitant to come out and saying what they think and what they want,” he said.

When it comes to some of their smaller, early grants, the group has been brutally honest in assessing its disappointments — an openness that has caused some tensions with nonprofits who aren’t used to such scrutiny.

“One thing I learned early on is that a well-placed donation can transform someone’s life, but a poorly placed donation can have no impact or even do harm,” Tuna said. “But it’s not at all obvious from charities’ marketing which are the best buys.”

The centerpiece of the team’s investigation is a giant spreadsheet, the origins of which can be traced to a Google Doc list Tuna began in 2011. She added causes as she thought of them: Malaria, microfinance, marijuana policy. The arts. Nuclear security, climate change and on and on until there were hundreds of entries.

Each topic is assigned to one of four researchers who work full-time — which include Tuna, Karnofsky and two other young whizzes from the country’s top colleges. They conduct “shallow” investigations of the ideas that involve making a few phone calls with experts and reading a few smart papers or journal articles on the subject.

They consider three questions when deciding whether a cause has promise. First, importance — how many people’s lives would be affected and by how much? Second, could it be solved, in the short-term and long-term? And third, how crowded is the space? If a lot of smart people are already thinking about the issue, the marginal impact could be less than in other areas.

If a topic passes this initial test, an in-depth investigation follows. That can take months and includes discussions with as many as 50 people in the field and an attempt to home in on what kind of specific project could make a difference.

Catastrophic risk and more

Asteroids, it turned out, were easy to rule out.

The team quickly learned that NASA tracks the big ones and the probability of mass destruction by the smaller ones is very small — 1 in 100 million for an extinction-level event like the one that killed the dinosaurs and 1 in 700,000 for one that would be considered a global catastrophe.

“Basically, NASA has this covered,” they concluded.

Other contenders seem inspired by old-time science fiction novels, though some are suddenly relevant because of technological advances: super volcanoes (risk of a catastrophe appears low), nuclear security (possible substantial risk of civilization-threatening damage), artificial intelligence (whose responsibility is it to think about what happens if computers become self-aware?), antibiotic resistance (issue gets a moderate amount of attention), climate change (can we geo-engineer our way out of this crisis by manipulating our atmosphere to reflect sunlight and make things cooler — or would that just make things worse?)

“We want to think about not only the people alive today but those will be alive in the future,” Tuna said.

Biosecurity — the constellation of issues around pandemics, bioterrorism, biological weapons and biotech research that could be used to inflict great harm, according to the group’s definition — may be among the most ripe for investment.

While “natural” pandemics like the flu seemed like the biggest threat right now, the team worried whether new technologies could pose a greater risk in time. The government has heavily invested in solutions, but everyone the team interviewed agreed that more needed to be done to, say, increase disease surveillance and strengthen public health systems in developing countries.

Another area the team has been exploring aggressively is U.S. policy.

A political science major in college, Tuna has been interested in what kinds of problems could be solved and which levers could be pulled to speed reform given the complexity of the political system in the country. In November, she organized an invitation-only brainstorming session for about a dozen policy wonks at a hotel in Washington where she got feedback on projects she is thinking about funding.

One of the topics they zeroed in on was criminal justice reform.

Tuna and her team were struck by two statistics: The United States incarcerates a larger percentage than almost any other country in the world at great fiscal cost and it has highest rate of criminal homicides in the developed world. Clearly something wasn’t working.

The team wondered whether there was way to reduce the number of people in prison in a way that is neutral or, better yet, positive for public safety. Could the solution lie in policing practices? Or other ways of stopping people from entering the system? Sentencing reform? Or something they haven’t thought of yet?

“There is growing interest on both sides of the aisle on reducing incarceration, and you don’t have that kind of opportunity for bipartisanship on a lot of issues right now,” Tuna said after the meeting.

Matt Cohler, a general partner at Benchmark, one of Silicon Valley’s most storied venture capital firms and a former colleague of Moskovitz at Facebook, said Tuna’s challenge is to say no to worthy causes because something else may be even more worthy.

“There are so many important things that need to be done in the world. People are approaching her all the time for help,” Cohler said. “It’s hard to stay focused and be very research-driven and thoughtful, and I admire that she has been able to do that.”

Tuna said that while she and Moskovitz’s approach may be analytical, that doesn’t mean there isn’t any emotion in their work.

To the contrary, “we’re really optimistic about the way the world is heading, about humanity’s progress,” she said.

“The world is a big, complicated system,” Tuna said, “and I feel we need to be as smart as we can be in order to stand a chance of having an impact with the resources we have — which are significant in one sense but really small in comparison to the kinds of the problems we want to work on.”