Why it can make sense to believe in the kindness of strangers

Would you risk your life for a total stranger?

While you might consider yourself incapable of acts of altruism on that scale, it happens again and again. During hurricanes and mass shootings, some people go to great lengths to help people they don’t even know while everyone else flees.

To learn whether this behavior comes more naturally to some of us than others, I partnered with Abigail Marsh and other neuroscientists working at the Laboratory on Social and Affective Neuroscience at Georgetown University. We studied the brains and behavior of some extraordinary altruists: people who have donated one of their own kidneys to a total stranger, known as nondirected donors.

[embedded content] Vox journalist Dylan Matthews explains in this video why he donated his left kidney to save a stranger’s life.

Unusually altruistic

These kidney donors may never learn anything about the recipient. That means they are not making this personal sacrifice because a relative or someone they may interact with in the future would benefit.

What’s more, this act of altruism is costly in multiple ways. It is a major, painful surgery. Many donors end up paying thousands of dollars out of pocket for medical and travel expenses, and they can lose out on salary and other earnings.

For the most part, there’s nothing to be gained in terms of the donor’s reputation. Many people, including some medical professionals, are skeptical about the motives of altruistic donors – even questioning their sanity.

These drawbacks help explain why altruistic kidney donation is extremely rare. Fewer than 2,000 people have done this to date in the United States since 1988, the first year with a recorded altruistic donor. That makes it something a mere one out of every 163,133 Americans have ever done.

And the norm is for living friends and family to donate kidneys to their loved ones. That was the case when celebrity Selena Gomez, who has lupus, got a new kidney from her best friend, the actress Francia Raisa.

Most commonly, the kidneys of deceased organ donors are used in transplants for strangers. There are about twice as many transplants from deceased donors as transplants from living ones.

Deceased donors and living friends and family account for a total of 99.5 percent of all kidney transplants performed over the past three decades.

Mammalian brains

Deep in the brains of all mammals – whether squirrel, bonobo or human – the same regions respond to distress and vulnerability. This response is especially common when babies cry out or appear threatened. In our most recent study, we investigated whether those brain systems, which are responsible for making all mammals care about helpless youngsters, play a key role in making some people extremely altruistic.

There are two major regions in what brain scientists call the “offspring care neural network,” evolutionarily old structures deep in the brain called the amygdala and the periaqueductal gray.

The amygdala is a small almond-shaped structure in both hemispheres tucked below the cortex. (Amygdala means almond in Greek.) One of its main roles in the brain is picking up on important emotional cues.

Research has long established that the amygdala is largely responsible for recognizing and feeling fear.

The periaqueductal gray is another small u-shaped structure at the base of the brain. It plays an important role in controlling basic behaviors like the impulse to cuddle a baby or the instinct to avoid predators.