If you’ve ever cooed at a baby, you have participated in a special experience. It’s a unique one: whereas humans constantly chatter to their infants, other apes hardly ever do so, a new study reveals.
“It’s a new feature that has evolved and massively expanded in our species,” said Johanna Schick, a linguist at the University of Zurich, Switzerland, and an author of the study. And that expansion may have been crucial to the evolution of language.
Other mammals can bark, meow, roar and hoot. But no other species can use a set of sounds to produce words, or build sentences with those words to convey an infinite variety of meaning. To trace the origin of our gift of language, researchers often study apes, our closest living relatives.
These studies hint that some ingredients of language had already evolved in the ancestors we share with apes. Chimpanzees can make dozens of distinct calls, for example, which they can join into pairs to communicate new things. Building meaning from smaller units is what lets us create sentences from words.
Baby talk — known to scientists as infant-directed speech — often features repeated words, an exaggerated stress on syllables and a high, singsong tone. This distinctive pattern is effective at grabbing the attention of young children — even when they’re too young to understand the meaning of the words. It’s possible that children pay attention to infant-directed speech because it helps them learn the basic features of language.
But the point in time when infant-directed speech evolved has long been a mystery, without any in-depth studies of wild apes. To gather that data, Franziska Wegdell of the University of Zurich travelled to Congo to observe bonobos. At the same time, Caroline Fryns, a behavioural biologist at the University of Neuchâtel in Switzerland and an author of the study, went to Uganda to observe chimpanzees. To round out their data on apes, the researchers used observations from earlier expeditions. Fryns had made observations of orangutans in Indonesia, while Lara Nellissen, a primatologist at the National Museum of Natural History in Paris, France, had watched gorillas in the Central African Republic.
The scientists gathered data not only on apes but also on children. Schick went to the Amazon rainforest in Peru to study an indigenous group known as the Shipibo-Conibo. She filmed a child each day, noting each time an adult spoke to him or her. The researchers also analysed similar observations made by other scientists in New Guinea, Nepal and the Swiss Alps.
The researchers discovered a stark difference between humans and apes: young apes hardly ever heard infant-directed communication. Even among chimpanzees, which chatter to one another on a regular basis, the adults might call just once to an infant over the course of an entire day.
Human children have a profoundly different experience with language. In every culture, children were spoken to by adults many times a day — every few minutes in some cases. The rate that children heard infant-directed communication was 69 times as high as what Fryns observed among chimpanzees and 399 times as high as what Wegdell observed among bonobos.
The researchers speculated that young apes learnt how to make calls by listening to adults. That was enough training to instil a relatively simple system of sounds. But when early humans began gaining a complex language, children needed more help. Talking to them a lot before they could speak may have enabled them to master the spoken word.
Marina Kalashnikova, a linguist at the Basque Centre on Cognition, Brain and Language in Spain, praised the study as a comprehensive analysis. But she also noted that the youngest child in the study was 11 months old, while most were between two and four.
“I think that the age of the children may have influenced both how adults speak to them and also how much,” Kalashnikova said.
It’s possible that the patterns the scientists observed in humans are different for babies in the first few months of life.
NYTNS