ROBERT CLONINGER: "If someone is repeatedly abused and neglected, they may form abnormal connections with what's rewarding. Some anti-social people actually become sadistic because of these traumatic past experiences. But that's an abnormal state of the brain."

Robert Sussman, the anthropologist, studies apes and other non-human primates as well as humans. He says there is another reason people might not help.

ROBERT SUSSMAN: "Humans have this thing when they think they're going to be sued. Many of the primates who live in social groups will automatically help in those situations, because they don't have all of these things that they've learned that they could be punished for doing that."

So what is the solution if fear of getting sued might stop someone from helping? Some activists call for more good Samaritan laws to protect people from lawsuits. But Sheldon Richman has another suggestion. Mr. Richman edits a journal, The Freeman: Ideas on Liberty, that teaches the principles of the free market. He says the solution is to change the system of civil law to not make it so easy to sue other people.

STEVE EMBER: Kristin Schroeder says she did not think about laws or lawsuits the day a woman collapsed at work.

KRISTIN SCHROEDER: "The ideas of laws just don't even go through my head in a situation like that. What's going through my head is, I want to help this person."

The woman was in her mid-twenties. She had suffered cardiac arrest -- her heart had suddenly stopped beating.