We've been to the moon, we've mapped the continents, we've even been to the deepest point in the ocean -- twice. What's left for the next generation to explore? Biologist and explorer Nathan Wolfe suggests this answer: Almost everything. And we can start, he says, with the world of the unseeably small.

Virus hunter Nathan Wolfe is outwitting the next pandemic by staying two steps ahead: discovering deadly new viruses where they first emerge -- passing from animals to humans among poor subsistence hunters in Africa -- before they claim millions of lives.