Noam Chomsky is considered a leader of modern linguistics and language study. Chomsky claimed that only humans could learn language. Scientists soon sought to test this theory, leading to dozens of experiments teaching various primates sign language, with mixed results. As of 2024, whether primates can learn language is still debated among scientists.

Kenneth Oppel drew on many experiments for Half Brother, but the story of Nim Chimpsky and Project Nim offered the most influence. Project Nim was a study conducted by psychologist Herbert Terrace from Columbia University (Adler, Margot. “The Chimp that Learned Sign Language.” NPR, 28 May 2008). Richard Tomlin, a character in Half Brother, is also a psychologist rather than a linguist.

In 1973, the same year Project Zan started in the novel, Project Nim began in New York. Terrace aimed to see if Nim could learn language like human babies, so he placed Nim with a family who signed with him regularly. Eventually, Nim became too much for the family to handle, and by 1977, Terrace ended the project. Although Nim learned 125 signs, Terrace argued that Nim was only imitating his handlers and did not sign spontaneously.