People first have to learn to speak – in the first few years of life they acquire this ability through experience and social interactions. But what about our relatives? Until now, the sounds and development of sounds in monkeys were largely innate and instinctive. But observations in common marmosets disprove this: They too develop their full communication skills only with time and depending on experience.
People are known to learn their language through experience and social interactions with others. The human vocalizations change dramatically, especially in the first year of life, and become more and more linguistic: What is initially shouts or a laugh soon becomes a babble and later the first words. In the case of monkeys, on the other hand, it was previously assumed that their development of sounds, gestures and facial expressions is largely predetermined with physical maturation and takes place within the first few weeks of life.
What is predetermined and what is learned?
One of the reasons for this: Earlier studies showed, among other things, that deafness or social isolation due to the absence of parents has little or no influence on the voice development of monkey children. Despite these obstacles, the animals appeared to develop a largely normal sound repertoire. “One of the reasons for these results is that previous work on voice development in nonhuman primates has mainly focused on the first few weeks after birth and ignored possible changes associated with later growth in the subsequent months up to adulthood “, Explains Yasemin Gültekin from the University of Tübingen.
In a study, Gültekin and her colleagues have now examined to what extent the later development of vocalizations in monkeys is more or less automatic. To do this, they observed the sound development of six common marmosets from early infancy to sexual maturity at the age of 15 months. During this period, the scientists recorded the vocalization behavior of the examined animals with microphones every month. In total, around 150,000 utterances were recorded and analyzed.
Flexible use of language through experience
The result: The previous ideas about the language development of monkeys do not seem to apply, at least with the common marmosets. “Our results show that the vocalization behavior of common marmosets, similar to the first few months of human life, changes through various stages of development from the first few weeks after birth to adulthood,” explains Kurt Hammerschmidt from the German Primate Center. All species-specific vocalization types are already present in the first month after birth and many developmental changes in the acoustic structure, such as the duration or frequency of calls, can largely be explained by physical maturation.
Nevertheless, experience in language acquisition was necessary. “While changes in acoustic structure could mainly be explained by physical growth or maturation, we found that the flexible use of these vocalizations over the course of development suggests experiential learning mechanisms, which are one of the key characteristics of human language development, ”says Gültekin.
It was shown, for example, that the young monkeys increasingly used a certain call as soon as they were no longer carried but ran independently. “The observed increase in calls could be due to the fact that the offspring are trying to get their parents’ attention,” the researchers said. “We also show that marmosets increasingly produce different and unique vocalization sequences as they mature, suggesting that different learning mechanisms underlie the development of call transitions.”
Human language evolution model
“These findings are evidence of a prolonged phase of plasticity during the vowel development of common marmosets,” the researchers sum up. In their view, the primate species thus represents a suitable animal model for examining the evolution of language more closely. “Our work provides an important building block for a better understanding of the evolutionary basis of human language development in early childhood,” explains Gültekin. “It creates the basis for future studies on how social interactions can influence language development.”
Source: Deutsches Primate Center GmbH – Leibniz Institute for Primate Research, Article: Science Advances, doi: 10.1126 / sciadv.abf2938