Nova

They may have stolen many hearts-and the internet-but cats can be perplexing pets. As much cuddly and playful as they are aloof and uncaring, they've often raised the question: Did humans ever really domesticate felines? And what more can science tell us about a relationship that predates history?

From fruit flies to whales, virtually every animal sleeps. But why? Why do we need to spend nearly a third of our lives in such a vulnerable, defenseless state? Scientists are peering more deeply into the sleeping brain than ever before, discovering just how powerful sleep can be, playing a role in everything from memory retention and emotional regulation to removing waste from our brains. So why are we getting so little of it?

Discover the ingenious engineering of Beijing's Forbidden City, the power center of imperial China for nearly 500 years. Discover how the design of this vast complex of palaces and temples enabled it to survive centuries of earthquake shocks.

For over 1000 years, chariots thundered across China's battlefields-dominating warfare longer than anywhere else on earth. Now, a series of amazing archaeological findings enable a team of experts to reconstruct and test China's first super-weapon.