Not all tales have happy endings, however. Corwin said that since he completed filming, timber companies have purchased the jungle sanctuary to which he’d helped transfer a group of Sumatran orangutans. “Unfortunately,” he said, “these types of stories are not going away.”

The film and the book repeatedly stress that humans are responsible for the extinction crisis, and only they have the power to stop it. Clearly, the last thing Corwin wants is for his next documentary to be called 50 Heartbeats.

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Curtis Brainard writes on science and environment reporting. Follow him on Twitter @cbrainard.