What role did the jungle play in humanity's distant past, and what can it tell us about our future? The final episode looks for clues among the primates of the rain forests as well as the traces of ancient civilizations that thrived there, only to vanish. For example, using 3-D infrared satellite imagery, the scientists piece together what might have happened to the lost civilization of Angkor Wat, Cambodia, tracing how the city's relentless expansion led to changes in climate and ecology and eventually to drought, starvation, warfare, and abandonment.