What role did the jungle play in humanity's distant past and what can it tell us about our future?

What role did the jungle play in humanity's distant past and what can it tell us about our future? The final installment of "Deep Jungle" looks for clues among the primates of the rainforests, as well as traces of ancient civilizations that once thrived there, only to vanish mysteriously. Included are expeditions to the Central African Republic, Guatemala and Cambodia.