Actor Danny Trejo is best known for his portrayal of villains in movies like Heat, Con Air, and Spy Kids, thanks in part to his gravelly growl of a voice and craggy face. But Trejo recently proved himself to be a real-life hero after he witnessed a terrifying car crash while out running errands. A sedan next to his car collided with an SUV, creating a chain reaction that flipped the SUV onto its hood. Inside lay a young boy with special needs, along with his mother and grandmother.

Trejo and another bystander leapt into action. Despite smelling gas trickling from the wreckage, Trejo crawled into the overturned SUV and worked furiously to extract the boy, then kept him calm while emergency crews freed his family. Afterward, Trejo remarked, “…People have to understand that God put us on this Earth to help each other… We are here to serve, we are here to welcome, we are here to love. That’s what we’re supposed to be doing. I’m just thankful to God because He let me do that today.”

Feats like Trejo’s often leave us both awed and perplexed. The pervasive belief that human beings are fundamentally selfish seems impossible to reconcile with the reality of ordinary people taking extraordinary risks to help strangers. As a result, real-life heroes are often seen as superhuman, saintly, or angelic. Many imagine them to be free of pedestrian emotions like panic and terror that motivate self-preservation. These stereotypes may reflect an underlying assumption that ordinary humans could never overcome fear for their own safety to help a stranger.

But recent advances in social neuroscience research suggest just the opposite. Research in my own and others’ labs is bringing into focus the unusual, but decidedly earthbound, processes that underlie the human motivation to help others, even in the face of significant risk or sacrifice.

Our first clue about what drives real-life heroes is that they often describe themselves as feeling decidedly un-stoic during rescues. Take Trejo, who later recounted his terror that the wrecked car would explode, saying, “The scariest thing in the world is to crawl into a car in that situation and you smell gas.”

Trejo’s recollection suggests a role for a brain structure called the amygdala in heroic rescues. The amygdala is an almond-shaped structure located in the temporal lobes of the brain (about an inch behind the eyeballs). The amygdala is involved in a wide range of social and emotional processes, but it’s probably best known for its role in coordinating responses to threats. Important sensory information about potential threats—the smell of leaking gasoline, for example—is conveyed rapidly to the amygdala. The amygdala then links that sensory input to learned information (for example, that gas leaks can cause explosions), triggering a series of signals to other brain regions – to coordinate a response.

Communication between the amygdala and an even more ancient region called the midbrain in response to a threat results in defensive behaviors such as freezing. In a 2017 study, rats that were repeatedly exposed to the smell of peppermint right before being shocked quickly came to freeze whenever they smelled peppermint.

But the researchers also discovered an important exception to this rule. The rats could overcome the self-protective urge to freeze in response to the smell of peppermint if baby rats were nearby. In this situation, the rats instead worked vigorously to protect the pups—dragging them back to the nest and huddling protectively over them, or furiously working to block the tube piping in the dangerous smell. The rats were not fearless; they still recognized the danger. Rather, they were brave—acting in the face of danger to protect vulnerable others.

The researchers traced the rats’ courage to the activity of a hormone called oxytocin in the amygdala. This hormone, which evolved to support parental care in mammals, seems to act like a switch in a railyard, shifting adult rats away from self-preservation and toward the protection of their vulnerable offspring.

Can what we’ve learned about parental care in rats help us understand human altruism? Perhaps.

There are notable similarities between a rescue like Trejo’s and the behavior of rats in the peppermint study. In both cases, adults smelled an odor they knew signaled danger. But rather than freezing or fleeing, they ran toward the danger to protect a vulnerable child—not because they were ignorant of the danger, but because they were keenly aware of it. And because parental care is strongly linked to altruistic motivation more generally, oxytocin’s effects in the amygdala are thought to motivate care for a wide range of other people, even unfamiliar others.

My research is highly consistent with this possibility. Although we can’t (yet) directly measure oxytocin in the amygdala in humans the way we can in rats, brain imaging studies indicate an important role for the amygdala in human altruism as well.

My research team has, for example, spent several years studying the brains of altruistic living kidney donors—people who have voluntarily given up a healthy organ simply because they know it could save a stranger’s life. This kind of extraordinary helping is painful and time-consuming, and it is not without risks. Using the brain imaging technique known as MRI, we find that these altruists’ amygdalas are larger than usual and more active than average in response to the sight of other people in distress.

Altruists also show stronger white matter connections between the amygdala and the midbrain. (white matter is the wiring between brain structures). This is important because, together, these regions regulate parental care in mammals through the action of oxytocin. Activity in these regions is also strongly linked to altruists’ desire to help others. Finally, we have found that altruists are better able to recognize and empathize with the fear of others—even total strangers.

Our findings show that people who take risks to help strangers are not insensitive to danger or fear. Rather, their desire to help others in distress overrides their natural concern for their own well-being. This desire may be rooted in ancient brain systems that humans share with other mammals that provide intensive care for their offspring.  And these systems can operate outside of conscious awareness. This helps explain why altruists—from heroic rescuers to the kidney donors we study—often describe their urge to help not as the result of careful, deliberate analysis, but more akin to “a bolt of lightning” striking.

So the next time you find yourself awed by an act of real-life altruism, resist resorting to supernatural or superhuman explanations. Instead, remember that far from being universally and irredeemably selfish, human beings may be endowed, thanks in part to their amygdalas, with the capacity for courage to help others in distress.   

Abigail Marsh is a social psychologist and cognitive neuroscientist who studies the social and neural underpinnings of costly forms of helping.