Chimpanzees who learned to say “mama”

Old recordings show captive chimpanzees saying the word, which some scientists believe may provide clues to the origins of human speech.

After analyzing video recordings of chimpanzees made several decades ago, scientists came to the conclusion that the animals can pronounce the human word: “mama.”

It's not quite the kind of raucous dialogue you'd see in this year's “Kingdom of the Planet of the Apes.” But it's a find, published Thursday in the journal Scientific Reports, may provide some important clues about how language evolved. The researchers say that our common ancestors with chimpanzees already had brains equipped with some of the elements needed for conversation.

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

“It's the one trait that explains why we've been able to change the face of the Earth,” says Dr Lameira. “Without it, we'd be unremarkable apes.”

Scientists have long wondered why we can talk and other apes can’t. Beginning in the early 1900s, this curiosity led to a series of bizarre — and cruel — experiments. Several researchers tried raising apes in their homes to see if living with humans would 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 “daddy,” “mummy,” “up,” and “cup.”

By the 1980s, many scientists had dismissed the experience of Vicky and other adopted monkeys. For one thing, separating infants from their mothers was likely to be traumatic. “It’s not something you can fund anymore, and for good reason,” says Axel Ekstrom, a speech scientist at KTH Royal Institute of Technology in Stockholm.

Ethical considerations aside, the adoption experiments failed to produce fluent speech. The animals had difficulty pronouncing even simple sounds. This significant difference in the abilities of humans and apes has sparked a debate: were chimpanzees unable to speak because of the anatomy of their vocal apparatus or because of the peculiarities of their brain?

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

But in 2016, a team of scientists took X-rays of vocalizing monkeys and found that the primates' vocal tracts were indeed “speech-ready.” This led some researchers to wonder if monkeys' brains just didn't have what it takes to make speech.

Some studies suggest that the human brain is exceptional because it can send coordinated commands to the jaws and throat. This evolutionary step may have allowed our 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 learn new sounds from others.

But the authors of the new study suspect that primates are underestimated. In his own studies of orangutans, Dr. Lameira has found that the apes can learn vocal sounds. For example, wild orangutans in neighboring groups make different sounds. In zoos, they have learned to imitate a janitor's whistle.

Mr Ekstrom also wondered whether scientists had been too quick to dismiss the adoption experiments as failures. No one had ever analysed the sounds Vicky and the other chimps made.

He began searching for records. Eventually, Mr. Ekstrom discovered that Vicky had appeared in a 1959 documentary. In the film, the young chimp says “daddy” three times and “cup” once.

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

But as Mr. Ekstrom reported last year, Vicky's “daddy” version was radically different from his own. She pronounced only two “p” consonants, with no vowels. She pronounced “cup.” [cup] exactly the same way, making only the “c” sound followed by a “p”.

“It's not a very compelling argument that chimpanzees learned to talk,” Mr. Ekstrom said.

Mr. Ekstrom and Dr. Lameira teamed up to find more footage. They found a short YouTube video 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 a woman's encouragement.

Nancy Nagel, a sanctuary board member for 30 years, confirmed that the chimp in the video was Johnny. “He was saying 'mama,' in a very raspy voice,” she said in an interview. “That's all he was saying.”

Then Mr. Ekstrom and Dr. Lameira found newsreel footage from 1962 of a chimpanzee in Italy named Renata. She, too, said something that sounded like “mama.”

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

“It's basically like a word,” Mr. Ekstrom says. “It's a very specific, very unique acoustic profile. It's not going to be confused with anything else.”

Mr. Ekstrom then played the tapes to 61 volunteers, who wrote down the sounds they heard. Most agreed that Renata and Johnny were saying “mama.”

The work is a good example of the battle of scientific arguments in the field of “ape language,” said Julia Fischer, a cognitive scientist at the German Primate Center in Göttingen, in an email. She was not convinced by the study's results. “The sounds the monkeys make have nothing in common with human speech,” she said.

Instead, Dr. Fisher suggested, Renata and Johnny might be making a standard chimpanzee sound known as a “raspy grunt.” [pant-grunt]”The simplest explanation is that they simply put two of these raspy grunts together to get a reward,” she said.

But Michelle Belik, a psychologist at Edge Hill University in Britain, says the findings suggest ancient apes may already have had some of the mental abilities needed 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 said.

Mr. Ekstrom does not believe that Johnny and Renata alone can solve the question of the origin of speech. “It clearly shows that some theories are too simple to take into account all the facts,” he says.

To find more clues, he is now studying the fossil record of our ancestors after they split from other primates. “This 'black box' spans about six million years, so it's quite large,” he says.