Monkeys depend on social interactions for language development

In the first year of life, humans make a dramatic transition in their ability to communicate. Language development among infants shifts from preverbal cues, such as laughing or crying, to babbling phrases that become increasingly complex. 

A new study from the German Primate Center has revealed that monkeys learn to communicate much in the same way as humans. The research, which was focused on common marmosets, is providing new insights into the evolution of language.

The experts report that the infantile development of vocalizations in common marmosets also includes an extended flexible phase, without which language development in humans would not be possible. 

Several factors that are critical for language development in humans include maturation, learning, and early social interactions with parents. For decades, it has been assumed that in monkeys, language develops exclusively as a result of physical growth and maturation – independently of social interaction.

For example, previous studies demonstrated that deafness or social isolation due to the absence of parents had little or no effect on the vocal development of nonhuman primates, and that vocal development in most monkey species is completed within a few weeks after birth.

“One of the reasons for these findings is probably that previous work on voice development in non-human primates has mainly focused on the first weeks after birth and ignored possible changes associated with later growth in the following months until adulthood,” said study first author Yasemin Gültekin.

The researchers studied the sound and language development of common marmosets from early infancy until sexual maturity at 15 months of age. During this period, nearly 150,000 vocalizations of six marmosets were recorded for analysis. 

“Our results show that, similar to the first months of human life, the vocalization behavior of marmosets changes through different developmental stages from the first weeks after birth to adulthood,” said study co-author Kurt Hammerschmidt, who analyzed the data.

“While changes in acoustic structure could be explained mainly by physical growth or maturation, we found that the way these vocalizations are used flexibly during development points to experiential learning mechanisms, which are one of the key features in human language development,” said study lead author Yasemin Gültekin.

“Our work provides an important building block to better understand the evolutionary foundations of early human language development. It sets the stage for future studies on how social interactions can influence speech development.”

The study is published in the journal Science Advances.

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By Chrissy Sexton, Earth.com Staff Writer