A red sweater does not a human make.

For his last documentary, director James Marsh found a once-in-a-lifetime character in Philippe Petit, the French high wire artist who pranced, twirled, and reclined between the rooftops of the Twin Towers in 1974. Man on Wire was perfectly executed — a suspenseful and subtle homage to 9/11 — but without Petit's exuberant retelling of his famous stunt, the film wouldn't have become one of the best documentaries of the past decade. For his latest effort, Project Nim, in competition here at Sundance, Marsh has found a central character nearly as compelling: a chimpanzee named Nim who, in the 1970s, was raised by humans and taught sign language. Columbia University's Herb Terrace, who led the experiment, hoped to prove that an ape could learn to communicate linguistically with humans.

When he was just two weeks old, Nim was taken from his mother and raised by Stephanie LaFarge, Terrace's grad student and former lover, in her Upper West Side home. No one in the house was fluent in sign language, nor were they particularly rigorous in their care of Nim. "It was the '70s," explains Jenny Lee, LaFarge's daughter, in the movie. In other words, they were hippies, and Nim was allowed to do whatever he wanted — including drink beer and smoke pot. So Terrace brought in another student, Laura-Ann Petitto, to discipline and teach Nim, who was becoming increasingly sexual as he grew up, humping everything in sight. But he wasn't the only horny one: A sexual relationship soon developed between Terrace and Petitto.

Terrace's libido is one of the running jokes in the film, but it's also used, however subtly, to draw one of many comparisons between humans and Nim — comparisons that, more often than not, are more favorable to the chimp. Nim's stay in Manhattan is just the beginning of his story, as he's relocated several times during his life, and almost always to a home more depressing than the last. This is partly due to his increasing size and ability to harm his caretakers, but also because he became increasingly useless to Terrace, whose eventual scientific conclusions were not what he had hoped for. Suffice it to say that Nim is not treated very well, though he's never entirely ignored, either.

Like any great documentary, Project Nim isn't just about the subject at hand; rather, it investigates mankind as a whole, questioning our motivations and assumptions, and frequently defies our preconceptions — in short, there are a lot of -ions herein. If Man on Wire was about the relentlessness and creativity of the human spirit, then Project Nim is about its limitations and naïveté. For all the change forced on Nim, he ends up impacting the humans' lives to a much greater degree.