Half Brother (2010) is a young adult novel by Kenneth Oppel. In the novel, Oppel combines and fictionalizes several experiments in which chimpanzees learned sign language to communicate. The story follows the Tomlin family as they adopt a baby chimpanzee to see if it can learn and use language. Through this experiment and its effect on the characters, the text explores the themes of family, belonging, animal rights, communication, individuality, and growing up. The novel won the CLA Book of the Year for Children, the CLA Young Adult Book Award, and the Ruth and Sylvia Schwartz Award. Half Brother is listed as an American Library Association Best Book for Young Adults.

This guide refers to the 2010 Kindle e-book edition published by Scholastic Inc. 

Content Warning: Both the source material and this guide contain descriptions of animal abuse, violence, and injury.

Plot Summary

Sarah Tomlin, a scientist and doctoral student, takes an eight-day-old chimpanzee from his mother for research experiments. While Sarah wants to research cross-species fostering, her husband, Richard, wants the young chimp to explore whether chimpanzees can learn and use language like humans.

While Sarah picks up the chimpanzee, Richard and his 13-year-old son, Ben, drive from Toronto to Victoria, Canada. The University of Victoria agreed to sponsor Richard's research, but Ben is frustrated over leaving his friends and home.

On Ben's 13th birthday, the movers arrive with the Tomlins' things. Shortly after, Sarah arrives with the chimpanzee, who they name "Zan" after Tarzan. The Tomlins settle into their new home and life with Zan. As part of the experiment, Richard and Sarah insist that Ben treat Zan like a little brother, which Ben initially resists.

Richard introduces Sarah and Ben to Dr. Godwin, the head of Richard's department. The Godwins pressure the Tomlins to send Ben to Windermere University School, a private school. Ben makes friends with David Godwin, who is a year older, and develops a crush on Jennifer Godwin, who is his age.

Ben also befriends Tim Borden, a neighbor who attends the public school. However, when Tim's friends encourage Ben to vandalize a construction site, Richard insists on sending Ben to Windermere.

The Tomlins start teaching Zan sign language, and the research project begins in earnest. Richard and Sarah hire several research assistants, including Peter McIvor, who bonds quickly with both Zan and Ben.

Ben adjusts to his new school and tries to establish himself as an "alpha male." Zan's first sign is to ask Ben for a hug. Ben tries to start a romantic relationship with Jennifer and seems to make progress.

Though Zan quickly learns signs, Richard wants more evidence. He installs hidden cameras in Zan's room and asks the assistants to teach Zan at a desk. Zan responds poorly to the change, signing less and throwing more tantrums.

The project fails to win a crucial grant, and Richard tries to control the project and Zan's behavior. He installs a "learning chair" with straps to confine Zan.

When Ben stays home sick, he hears Zan screaming. Ben interrupts the research assistants and frees Zan from the chair. When one assistant grabs for Zan, Zan bites his finger down to the bone. Richard removes the learning chair.

Zan turns 1, and a TV news program films him. However, when the episode airs, it shows pictures of the learning chair and accompanying harsh criticism from animal rights activists. Ben's relationship with Jennifer ends when he discovers she used him to make her crush jealous.

Richard ends the project, stating that Zan is learning words, not language. The University of Victoria sells Zan to Siegal University of Nevada, placing him in their primate program under Jack Helson. The Tomlins go with Zan to ease the transition but worry about Helson's methods. Peter transfers to Siegal University to help Zan.

At the start of summer, Sarah and Ben return to see Zan. Peter expresses concern that Helson is in contact with a biomedical research firm. After opening a stolen letter, they learn that Helson intends to sell Zan and two other young chimps for medical research. Sarah and Ben steal Zan and bring him back to Victoria.

Upon arrival, Richard argues that Helson is within his rights to sell Zan, but he eventually relents. The Tomlins try to buy Zan from Helson, but he asks for an astronomical price. The Tomlins talk to several media outlets to raise money. They raise $12,000 of the required $20,000, but Helson refuses to sell, claiming defamation.

Ben runs away with Zan to a nearby forest. A few kids find them and become aggressive. Ben tries to escape by climbing a tree but almost falls. Zan saves Ben by grabbing his hand but breaks all of Ben's fingers.

Ben undergoes surgery but may never regain full use of his hand. News outlets intercept Helson's agreements with the biomedical lab, and media pressure convinces Helson to sell Zan.

The Tomlins take Zan to a chimpanzee sanctuary in Florida. Ben dreams of signing with Zan. Zan says he is happy in the sanctuary and understands why he could not stay with the Tomlins. Ben and Zan sign that they love each other for the first time.