New Duranty: She spent her early years playing in the backyard of a small house in Reno, Nev., learning American Sign Language from the scientists who adopted her, and by age 5 she had mastered enough signs to capture the world’s attention and set off a debate over nonhuman primates’ ability to learn human language that continues to this day.

But on Tuesday night, Washoe, a chimpanzee born in West Africa, died after a short illness, said Mary Lee Jensvold, assistant director of the Chimpanzee and Human Communication Institute at Central Washington University in Ellensburg, where Washoe had lived and learned for more than two decades. The chimp died in bed at age 42, surrounded by staff members and other primates who had been close to her, Dr. Jensvold said.

Scientists had tried without success to teach nonhuman primates to imitate vocal sounds when R. Allen Gardner and Beatrix T. Gardner, cognitive researchers, adopted the 10-month-old chimp from military scientists in 1966. The Gardners, skeptical that other primates could adequately speak human words, taught Washoe American Sign Language, encouraging her gestures until she made signs that were reliably understandable...

Language scientists around the world began their own projects, to try to replicate and extend the Gardners’ findings. But the excitement died down in the late 1970s, when Herbert Terrace, a cognitive researcher at Columbia, published a report on a chimpanzee he had been trying to teach language, named Nim Chimpsky. Nim could learn signs, but did so primarily by imitating teachers, Dr. Terrace found by reviewing videos of interactions.

“There was no spontaneity, no real use of grammar,” Dr. Terrace said. He analyzed a video of Washoe, who learned about 130 signs, and said he found evidence that she, too, was reacting to prompts, not engaging in anything like human conversation...