Saturday, April 21
Stress may save your life if you're being chased by a tiger. But if you're stuck in traffic, it may be more likely to make you sick. This hour, a long hard look at the body's system for getting out of trouble.

Saturday, April 28
To what extent is color a physical thing in the physical world, and to what extent is it created in our minds? We start with Sir Isaac Newton. Then, we meet a sea creature that sees a rainbow way beyond anything humans can experience, and we track down a woman who we're pretty sure can see thousands more colors than the rest of us. And we end with an age-old question: why is the sky blue?