Some people like to dangle off cliffs. Others kayak down killer rapids. In this hour of To the Best of Our Knowledge, why people are driven to push the limits. Also the story of Jerri Nielson, the doctor stranded at the South Pole who discovered she had breast cancer, and then treated herself.

Environmental writer Bill McKibben tells Jim Fleming about his decision to push himself to become a world class cross country skier. He explains that his training took a year, during which he also had to cope with his father's death. McKibben's book about the project is "Long Distance." Also, Niles Goldstein is the founding rabbi of the New Shul in New York and the author of "God at the Edge: Searching for the Divine in Uncomfortable and Unexpected Places." He tells Anne Strainchamps about two stops on his own spiritual path.

Mountain climber Rick Ridgeway tells Steve Paulson what it felt like to be caught in high mountain avalanche, and why he keeps climbing. His book is "Below Another Sky," which chronicles the trip he made to Tibet with the daughter of the friend killed in the avalanche he talks about. Also, Oxford University physiologist Frances Ashcroft explains to Jim Fleming exactly what goes on in the human bloodstream at high altitude or great underwater depth. Ashcroft's book of scientific curiosities is "Life at the Extremes."

Dr. Jerri Nielsen went to the South Pole for one year, during which she discovered that she loved the environment and the community of scientists there, and that she had breast cancer. She tells Steve Paulson what was so great about being stranded in the middle of nowhere, and how her colleagues helped her diagnose and treat her illness. Nielsen's best-selling memoir is "Ice Bound."

Distribution dates:

• week of 04/01/2001 - hour 1