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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. Part 1, "First Steps," examines the factors that caused us to split from the other great apes. The program explores the fossil of "Selam," also known as "Lucy's Child." Paleoanthropologist Zeray Alemseged spent five years carefully excavating the sandstone-embedded fossil. NOVA's cameras are there to capture the unveiling of the face, spine, and shoulder blades of this 3.3 million-year-old fossil child. And NOVA takes viewers "inside the skull" to show how our ancestors' brains had begun to change from those of the apes. Why did leaps in human evolution take place? "First Steps" explores a provocative "big idea" that sharp swings of climate were a key factor.