Would you donate a kidney to someone you've never met? The idea is layered with soul-searching judgments — questions of risk and benefit, sacrifice and selfishness, not to mention the physical pain of the surgery itself.

But a small number of people have done this, and researchers at Georgetown University are studying them, providing a window on altruism in a world seemingly dominated by a me-first philosophy.

“Extraordinary altruists,” as the researchers call them, come from all age, race and socioeconomic groups. Some are religious, others are not. But unlike almost everyone else, they don't see less value in a stranger's life than in the life of a close friend or relative, the researchers found. And they are genuinely puzzled that the rest of the world doesn't view other people the same way.

“They don’t see it as something necessarily heroic or that they should be given praise for,” said Kruti M. Vekaria, a doctoral student in psychology who was part of the team that conducted a study published Friday in the journal Nature Human Behavior. “They think it’s something everybody should do.”

When asked directly why they would give up a kidney to a perfect stranger, “they see it as an obvious choice,” added Abigail A. Marsh, a psychologist at Georgetown who led the research team. “They just seem politely puzzled. They have trouble answering the question.”

Altruism is difficult to study because most generous acts, such as giving to charity, carry some benefit for the donor (a tax break, for example). And small, kind gestures, such as holding a door open, are partly determined by social norms.

But undergoing a surgical procedure and increasing one's own risk of future health problems is “painful, costly, non-normative, exceedingly rare and meets the most exacting definitions of costly altruism,” the authors wrote.

“When we’re personally touched by something, that’s when we react to it,” said Angela Cuozzo, a 49-year-old from Albany, N.Y., who gave a kidney to a 25-year-old woman in Bakersfield, Calif., seven years ago. “We should take it upon ourselves to be a little more forthcoming and pay it forward before we’re personally touched by it.”

Cuozzo said that she was single with no children and going through a minor midlife crisis when she overheard a co-worker discussing his sister's fourth kidney transplant. She began to research the idea of giving a kidney and discovered that she could participate in a chain kidney donation if she gave to a stranger. In that arrangement, organizers try to maximize the number of kidneys donated by having a friend or relative of each recipient give an organ to someone with whom they are a match, but strangers can donate as well.

“I just really needed to make sure that before I left this Earth I could somehow contribute,” Cuozzo said. Her donation eventually went to the California woman, not the co-worker's sister.

Rob Upham, who gave a kidney to a woman in 2009, said he first thought about the idea after watching a news report on chain kidney donations. The oldest person in the chain was 72.

“I just thought 'why hadn’t this dawned on me before? I have two healthy kidneys and I can possibly save someone’s life, or at least improve the quality of somebody’s life,” said Upham, 52, director of human resources for an organization that provides services to Rhode Island's homeless.

He said he sees nothing extraordinary in what he did and never worries about his own health. No one in his family has had kidney problems.

“Most people live in a wooden house. It might burn down. You still live in a wooden house. Life is filled with risk,” he said.

Upham said he met the woman who received his kidney in the hospital, three days after the transplant. She died three months later of a stroke. But he has no regrets. He went to her funeral, where he was called “an angel” during the eulogy.

Vekaria said about 2,100 people had given kidneys to strangers out of a total of about 147,000 live donations at the time the research was conducted.

There is a drastic shortage of transplant organs in the United States. According to the United Network for Organ Sharing, 97,727 people are waiting for kidneys as of this week, and an additional 20,000 need livers, hearts, pancreases or other organs.

Previous research by Marsh has established that extraordinary altruists have larger than normal amygdalas, a portion of the brain involved in compassion. (Psychopaths have smaller than normal amygdalas, she said). In brain scans, that part of altruists' brains also appears to be more active than in average people when they are considering questions of altruism, she said.

But that doesn't explain much, because the technology used to visualize brain activity is relatively crude and compassion for others is learned as one goes through life, she said.

In the current study, the team compared 21 kidney donors with 39 control subjects. First, they asked them to place avatars representing family, friends, neighbors and strangers on a computer screen at distances from an avatar for themselves, to test their views of “social distance” — whether they consider themselves closer to strangers than most people do. They found that there is no significant difference between altruists and others.

Then the researchers asked people to play a money allocation game. In each round, they could keep larger sums for themselves by declining to give part of the money to another person — a family member, a friend or a stranger, for example. Or they could give some money away, resulting in less for themselves.

The altruists consistently placed more value on strangers than ordinary people did. The altruists gave as much money to very distant strangers as control group members gave to a good acquaintance, for example.

That helped researchers conclude that the altruists simply don't value strangers less than they value people they are close to. “They don’t tend to view a stranger or even an acquaintance as any less deserving of resources,” Vekaria said.

In an article that accompanies the study, Tobias Kalenscher, who studies comparative psychology at Heinrich Heine University in Düsseldorf, Germany, praised the research for its insights on altruism. But he noted that it still does not explain why altruists hold such views of strangers. And he wondered whether the outcome of the experiment might have been different if the study had used real money.

Still, he wrote, “In today’s zeitgeist of nationalist protectionism and populist individualism, this news inspires hope for the future.”

Extraordinary altruists receive no benefits from their donation and face some costs. The kidney donors often receive pressure from family and others who worry about their health. Some of their loved ones express concern that the organ won't be available if a relative needs it in the future, Marsh said. Cuozzo, who married after her donation, said her husband has told her that he would have strongly opposed the idea if he had known at the time.

Cuozzo did not discuss her decision with family and close friends until she was about to undergo surgery. Most were supportive, but without the enthusiasm she felt. One who works in health care was openly opposed.

“I like to say that maybe I’m a little more compassionate and that has at times” been a disadvantage, she said. At work, Cuozzo, a graphic designer, said she is sometimes not assertive enough and has paid a price professionally.

“I’ve often had people say 'you've got to  stop thinking about everybody else and focus more on yourself'," she said.

At 49, she remains in good health, her day-to-day existence largely unchanged by the donation, she said. Except that “it was the most amazing experience of my life to this day,” she said.

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