Why did the Incas abandon their city in the clouds?

Find out what scientists know about dreams: what they are and why we have them. 8/22/2012

Where did we come from? What makes us human? An explosion of recent discoveries sheds light on these questions, and NOVA's comprehensive, three-part special, "Becoming Human," examines what the latest scientific research reveals about our hominid relatives.

NOVA examines the fate of the Neanderthals, our European cousins who died out as modern humans spread from Africa into Europe during the Ice Age. Did modern humans interbreed with Neanderthals or exterminate them? The program explores crucial evidence from the recent decoding of the Neanderthal genome.

NOVA investigates the first skeleton that really looks like us–"Turkana Boy"–an astonishingly complete specimen of Homo erectus found by the famous Leakey team in Kenya. These early humans are thought to have developed key innovations that helped them thrive, including hunting large prey, the use of fire, and extensive social bonds.

First Steps: 6 million years ago, what set our ancestors on the path from ape to human? The first part of NOVA's comprehensive, three-part special "Becoming Human" examines the factors that caused us to split from the other great apes. The television program premiers on PBS on Tuesday, November 3rd.

Bill Nye, TV's "Science Guy," conducts a pasta-making experiment that can save energy.

Is the weather on Mars anything like the weather on Earth? Find out in this video.

On February 1, 2003, the space shuttle Columbia disintegrated just 16 minutes before it was due to land. All seven astronauts aboard perished, and the implications for the future of the space shuttle program were enormous. Through interviews with astronauts and their families, and with members of the Columbia Accident Investigation Board, take a look at the Columbia tragedy — and at NASA itself.

Tom and Ray test out the waters of Iceland's Blue Lagoon while filming "Car of the Future."

A researcher tests the cognitive skills of a chimpanzee with a seemingly simple task.

Primatologist Brian Hare sees whether a bonobo can solve a puzzle to get a slice of apple.

Black chemist Percy Julian met with every possible barrier in a deeply segregated America. Here's how he rose to the highest levels of scientific and personal achievement.

Watch visualizations of ideas that helped Einstein devise his theories of relativity and of the equivalence principle.