Optimus Primate: Nim was a very impressive chimp.

Has an ape ever made you cry? You just might shed a tear for Nim Chimpsky, the chimpanzee whose fate is detailed in James Marsh’s documentary Project Nim. He was plucked out of his tranquilized mother’s arms in 1973, sent to live with a family in New York’s Upper West Side, and taught sign language in what was a nature/nurture experiment designed by Columbia University animal cognition scholar Herbert Terrace. Nim’s new mother, an upscale hippie named Stephanie, breastfed him and “wasn’t concerned with discipline.” Nim didn’t get along with Stephanie’s husband and antagonized him; he was generally allowed to run around and destroy things as he pleased. Stephanie gave him alcohol and pot. Laura, a research assistant sent to aid Stephanie early in the project, described the atmosphere as “utter chaos.”

But the lot of them (the couple had several other children) managed to teach Nim how to communicate and, always dressed in kid’s clothes, he became one of the family. Which made it that much more devastating when Terrace decided to remove Nim to an estate in Riverdale, N.Y., where the professor along with Laura and a few new teachers raised Nim and continued his education. As well as theirs: As Nim became older, they realized the importance of asserting dominance over the chimp, though there were of course mishaps—like when Nim lunged at Laura and pounded her head into pavement. “You don’t give human nurturing to an animal that could kill you,” she now says.

Home videos and old photos comprise the bulk of Project Nim, along with recent interviews with Terrace and several of his assistants. They detail an almost idyllic time caring for an ape who, for the most part, became a charming companion and addition to their lives. Look at him put on his own shorts! Look at him hugging a cat! Aww. The cute factor—and seeming success of the language experiment—outweighs eye-rolling canned commentary like “As much as we were molding him, he was starting to mold us.” Also unnecessary: Weird flourishes like Nim’s vocabulary scrawled across the screen. The director can also get melodramatic, as with one scene involving a medical experiment, in which a chimp receives a shot on a hospital bed before the camera pans to a piece of paper on the wall illustrating the sign for “play.”

Yes, the medical experiments: Things aren’t always brownstones and bananas for Nim. When Terrace abruptly ends the project, Nim is treated like just another chimp, and his experiences over the next decade or so will break your heart. The documentary as a whole is fascinating, an illuminating look at how close we really are to our animal brethren, how a nugget of nature may be unchangeable, but how chimps—and, by extension, us—are moldable by our surroundings. Nim as a project may have been limited to one ape, but the ramifications are universal.