Abigail (Abby) Marsh

And I thought maybe how humble they were about their choice to donate was sort of just a quirky little bug.

But I now believe it's an intrinsic feature of the decision to help other people.

Many donors I've worked with, I would say most donors, including Harold,

have told me that they're happy to take part in my research.

They're glad I'm doing it, but they're pretty sure I'm not going to find any differences between them and other adults because there's nothing special about them or anybody else who wants to donate a kidney.

It's just a function of having the right information, being in the right place at the right time.

It's something anybody could do.

And I've had many altruists reassure me that there's nothing special about them.

And that to me makes perfect sense because if you really do believe that you're the most special person, why would you want to share with somebody less special?

That doesn't make any sense.

The most special person should have all the kidneys.

But if you're such a humble person that you don't think you're any more special than anybody else, it does make complete sense that you would say, well, why should me, who's not in any way special, have all the kidney resources?

It really makes much more sense to allocate them among anybody who happens to need one.

I'm familiar with Danny Trejo from his role in Spy Kids, where he plays a villain, as he often does in the movies, because he has this very gravelly sounding voice and a craggy face and looks very forbidding.

And so he usually plays villains in the movies.

And so how did he come to your attention as an altruist?

Well, he was in the news for something very altruistic and heroic that he did.

He was running errands, I think, near his home one day when he witnessed a terrifying car crash when a sedan next to his car collided with an SUV and it resulted in this chain reaction that flipped this SUV upside down and inside was trapped a little boy who I believe had special needs along with his mother and his grandma.

And Trejo, as is often the case in these situations, reacted immediately.

He could smell gas trickling out of the wreckage of the cars.