GWEN IFILL:

For many, the debate over what is true and what is believable extends far and wide. According to the Pew Research Center, 86 percent of scientists think childhood vaccines should be required. But just 68 percent of U.S. adults agree.

On another hot-button issue, climate change, the gulf is even wider; 87 percent of scientists believe climate change is caused by human activity. Only half of adults agree. The biggest gap in the Pew survey: the safety of genetically modified foods; 88 percent of scientists say they're OK to eat, but only 37 percent of adults surveyed buy into that.

No matter what the scientists say, the disconnect extends to other issues as well, including evolution and the value of using animals in research.

National Geographic magazine's March cover story tackles those issues.

We're joined by its author, Joel Achenbach, a writer for The Washington Post, and Cary Funk, the associate director of research at the Pew Research Center, who came up with some of those interesting numbers we just saw.

Joel, why is nothing settled?