We are all Russian nesting dolls: Our intestines house many bacteria, which house many viruses. These so-called bacteriophages are likely as important for our health as the bacteria they live in. Lisa Brown for NPR hide caption

itoggle caption Lisa Brown for NPR

Helping employees take the time to go for a walk instead of reaching for junk food when energy flags boosts productivity, some firms find. Jamie Grill Photography/Tetra Images/Corbis hide caption

itoggle caption Jamie Grill Photography/Tetra Images/Corbis