Chimpanzees Who Learned To Say the Word "mom"

There are old recordings that show captive chimpanzees saying the word "mom," which some scientists believe may provide clues to the origins of human speech.

After analyzing video footage of chimpanzees from decades ago, researchers have concluded that these animals can say some words. It's not exactly maintaining dialog, as depicted in this year's movie "Planet of the Apes: A New Realm." But the finding, published Thursday, July 25, 2024, in the journal Scientific Reports, may provide some important clues about how speech evolved.

Adriano Lameira, an evolutionary psychologist at the University of Warwick in the United Kingdom and one of the study's authors, says the ability to talk is perhaps the most important trait that distinguishes humans from other animals. Talking to each other allowed early humans to cooperate and accumulate knowledge over many generations.

"This is the only trait that explains why we were able to change the face of the Earth," says Dr. Lameira. "Without it, we would be unremarkable apes."

Scientists have long wondered why humans can talk and monkeys can't. Beginning in the early 1900s, this curiosity led to a series of strange - and cruel - experiments. Several researchers tried raising monkeys in their homes to see if living with humans could cause the young animals to start talking.

For example, in 1947, psychologist Keith Hayes and his wife Katherine adopted a baby chimpanzee. They named her Vicky and, when she was five months old, began teaching her words. After two years of training, the couple claimed, Vicky could say the words "daddy," "mommy," "up," and "cup."

By the 1980s, many researchers were questioning and refuting the experiences of Vicky and other foster monkeys. For one thing, separating cubs from their mothers was likely traumatic. "It's not something that can be compensated for, and not without reason," says Axel Ekstrom, a speech scientist at the KTH Royal Institute of Technology in Stockholm.

Ethics aside, the adoption experiments did not result in the development of fluent speech. The animals struggled to pronounce even simple sounds. This gulf in human and ape abilities has sparked debate: were the chimpanzees unable to speak because of the anatomy of the vocal apparatus or because of the brain?

For decades, Philippe Lieberman, an anthropologist at Brown University, has made a compelling case for the vocal tract. In 1969, he noticed that the human larynx and tongue were located lower in the throat than in other primates. Dr. Lieberman, who died in 2022, argued that this anatomical shift allows humans to produce the wide range of sounds needed for complex speech.

But in 2016, a group of scientists took X-rays of vocalizing monkeys and found that the primate vocal tract was indeed "speech-ready." This led some researchers to speculate that the monkeys' brains lacked something essential for speech.

This evolutionary step may have allowed human ancestors to combine consonants and vowels into syllables, which could then be combined into words. And humans, unlike the vast majority of other animals, can also learn new sounds from others.

But the authors of a new study suspect the primates are underestimated. In his own research on orangutans, Dr. Lameiro has seen that the apes are capable of learning vocal sounds. For example, wild orangutans in neighboring groups make different sounds. In zoos, they have learned to imitate a janitor's whistle.

Speech scientist Ekstrom also wondered if scientists had been too quick to dismiss the adoption experiments as failures. No one had ever analyzed the sounds that Vicky and the other chimpanzees made.

He began looking for footage. Eventually, Mr. Ekstrom discovered that Vicky appeared in a 1959 documentary. In the movie, the young chimpanzee appears to say "papa" three times and "cup" once.

Mr. Ekstrom recorded himself saying the words "daddy" and "cup" and then compared his voice to Vicky's. Every time she said "daddy," she made the same sound, indicating that she had indeed learned to say something new.

But as Mr. Eckstrom reported last year, Vicki's version of the word "papa" was radically different from his own. She pronounced only two "px" sounds, no vowels. She pronounced "cup" the same way, making only a "ch" sound followed by a "shk" sound.

"It doesn't look convincing, especially if you're trying to say, 'Look, this chimp has learned to talk,'" says Ekstrom.

Mr. Ekstrom and Dr. Lameira teamed up to find other footage. They found a short video on YouTube of a chimpanzee named Johnny, who lived at the Suncoast Primate Sanctuary in Palm Harbor, Florida. In the video, anonymously uploaded in 2007, Johnny appears to say "mama" in response to encouragement from a female.

Nancy Nagel, a sanctuary board member for 30 years, confirmed that the chimp in the video is Johnny. "He was saying a very hoarse 'mama,'" she said in an interview. "That's all he could say." Then Mr. Ekstrom and Dr. Lameira found a 1962 newsreel of a chimpanzee from Italy named Renata. She, too, uttered something similar to "mama."

In the new study, scientists analyzed how Johnny and Renata pronounced the word. Their sounds most closely resembled Mr. Eckstrom's version of "mama." Unlike Vicky, both Johnny and Renata could add a vowel after a consonant.

"It's basically like a word," Ekstrom says. "It's a very specific, very unique acoustic profile. You can't mistake it for anything else." Eckstrom then played the recordings to 61 volunteers who recorded the sounds they heard. Most of them agreed that Renata and Johnny were saying "mama."

"This work is a good example of the tug-of-war in the field of 'monkey language," said Julia Fischer, a cognitive scientist at the German Primate Center in Gottingen. She was not convinced by the study's findings. "What monkeys do vocally has nothing to do with human speech," she argues.

Instead, Dr. Fisher suggested, Renata and Johnny may be making a standard chimpanzee sound known as the "punt-grunt." "The simplest explanation is that they simply put two of these pant-grunts together and were rewarded for it," she said.

But Michelle Belic, a psychologist at Britain's Edge Hill University, says the findings suggest that ancient apes may have already possessed some of the mental abilities necessary for speech. "Humanity, despite all its peculiarities, did not emerge from under a rock but was molded by evolution from the clay of our primate ancestors," he says.

Mr. Eckstrom doesn't think Johnny and Renata alone can settle the question of the origin of speech. "This clearly shows that some theories are too simple to account for all the facts," he says. To find new clues, he is now studying fossils of human ancestors after they separated from other primates. "This 'black box' covers about six million years, so it's quite capacious," he says.