In various human cultures and languages, adults have a distinct way of communicating with babies. They alter the pitch and range of their voices, shorten and repeat their speech, and this even occurs in sign language. This style of speech, known as “motherese” or “baby talk,” is used not only by mothers but also by fathers, older children, and other caregivers. Infants show a preference for listening to this exaggerated and melodic form of speech, which may aid in bonding with adults and accelerating language development.
To truly comprehend the purpose and evolution of baby talk, it is crucial to investigate whether other animals employ similar communication techniques. While great apes do not seem to use baby talk vocally, they may use equivalent gestures. Squirrel monkeys and rhesus macaques use special calls when communicating with their young, although these calls differ significantly from human baby talk. Zebra finches display similarities to humans when singing to juveniles, inserting longer pauses between musical phrases and repeating introductory notes. Greater sac-winged bat mothers also modify their pitch and timbre when communicating with their offspring, but it is uncertain whether they use a distinct call or something analogous to baby talk. To definitively establish the latter, a species that uses a standardized, identifiable call for both infants and older peers would need to be studied, such as dolphins.
Bottlenose dolphins possess their own unique signature whistle, which is akin to a human name and is the closest approximation found in any animal. Dolphins can identify individuals through these whistles and sometimes imitate each other’s whistles, potentially as a form of address. They frequently utilize these whistles to announce their location when separated from their pod or as an introduction when encountering new groups. Calves develop their own signature whistles based on those they hear in their surroundings, and these whistles can remain unchanged for at least 12 years.
Laela Sayigh, a zoologist at the Woods Hole Oceanographic Institution, has been studying the signature whistles of bottlenose dolphins in Sarasota Bay, Florida since 1986, as part of the world’s longest-running study of wild dolphins. Sayigh and her colleagues regularly capture these animals to assess their health and record their calls before releasing them. During these captures, mothers and calves sometimes interact and exchange signature whistles. By analyzing 19 such incidents recorded over 34 years, Nicole El Haddad, a student of Sayigh, demonstrated that mothers raise and broaden the pitch of their signature whistles when calling to their calves, similar to how humans modify their voices when speaking to babies.
The consistency of this effect astounded Sayigh, who noted that dolphins’ intelligence and strong personalities often lead to unpredictable behaviors, making it challenging to identify clear patterns in their data. Sabine Stoll, a language evolution researcher at the University of Zurich, described the data as extraordinary and impressive. While dolphin baby talk differs from human baby talk – dolphin whistles do not become more repetitive – it represents the most compelling example of child-directed communication observed in nonhuman animals thus far, according to Mirjam Knörnschild from the Museum of Natural History in Berlin, who led a study on sac-winged bats. Its existence in a species separated from humans by over 90 million years of evolution is likely a remarkable demonstration of convergent evolution, as stated by Stoll.
If both species independently evolved baby talk, it is plausible that they did so for similar reasons. Human parents can capture their infants’ attention more effectively through high-pitched baby talk than through regular speech, and dolphin mothers may employ a similar strategy. Keeping their signature whistle intact while raising its pitch allows a mother dolphin to unequivocally communicate, “This whistle is meant for you,” to her calf. The specificity of this communication enables them to maintain close contact in a noisy ocean where numerous dolphins may be vocalizing simultaneously.
Human baby talk is also believed to strengthen the bond between babies and their caregivers and facilitate language learning by emphasizing important aspects of spoken words. This may also apply to dolphins, which spend a significant amount of time with their mothers and acquire vocalizations by listening to their peers. However, testing these hypotheses would be extremely challenging without separating mothers from their calves, a practice that would cross ethical boundaries. Sayigh has demonstrated the existence of dolphin baby talk, but the exact function of this communication remains unanswered.
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