When Abigail Marsh was 19, a complete stranger risked his life to save her from a car accident. Today, she studies what motivates us to help others -- and why some of us are "extraordinary" altruists.

At the prison where Cheryl Steed works, certain inmates are chosen to be caregivers for elderly inmates. The program has made her wonder -- can altruism be learned?

Philosopher Peter Singer's work focuses on "effective altruism" -- how to do the most good to make the world a better place. He argues effective giving involves balancing empathy with reason. Peter also speaks about the ethical merits of choosing a career on Wall Street in order to earn more and give more to effective charities.

Larissa MacFarquhar writes about extreme altruists, people who make great sacrifices to help others. She says most of us aren't prepared or willing to do that -- which is why we don't give more.