Who’s the Cutest Little Dolphin? Is It You?

Across human cultures and languages, adults talk to babies in a very particular way. They raise their pitch and broaden its range, while also shortening and repeating their utterances; the latter features occur even in sign language. Mothers use this exaggerated and musical style of speech (which is sometimes called “motherese”), but so do fathers, older children, and other caregivers. Infants prefer listening to it, which might help them bond with adults and learn language faster.

But to truly understand what baby talk is for, and how it evolved, we need to know which other animals use it, if any. The great apes don’t seem to vocally, but might use a gestural equivalent. Squirrel monkeys and rhesus macaques use special calls when talking to youngsters, but they’re very different from human baby talk, which is a modified version of normal speech. Zebra finches are closer to us: When singing in front of juveniles, adults add longer pauses between musical phrases and repeat introductory notes. Greater sac-winged bat mothers also change their pitch and timbre when signaling to pups, but again, it’s hard to tell if they’re using a distinct call or doing something analogous to baby talk. To make an inarguable case for the latter, you’d need to study a species that talks with both infants and older peers using the same standardized, identifiable call. In other words, you’d need a dolphin.

Every bottlenose dolphin produces its own unique signature whistle, which is the closest thing any animal has to a human name. Dolphins can recognize individuals through these whistles and will sometimes copy one another’s, perhaps as a form of address. They use their whistles frequently, to announce their position when separated from their pod, or as an introduction when meeting up with new groups. Calves develop their own signature whistles based on those they hear around them, and once learned, the whistles can go unchanged for at least 12 years.

Laela Sayigh, a zoologist at the Woods Hole Oceanographic Institution, has been studying the signature whistles of bottlenoses in Sarasota Bay, Florida, since 1986 as part of the world’s longest-running study of wild dolphins. She and her colleagues regularly catch these animals, check their health, and record their calls before releasing them. Sometimes, they catch mothers and calves together, and the animals exchange signature whistles throughout the process. By analysing 19 such moments, recorded over 34 years, Sayigh’s student Nicole El Haddad showed that mothers raised and widened the pitch of their signature whistles when calling to their calves, just as humans do when talking to their babies.

“We were just blown away by how consistent the effect was,” Sayigh told me. Between their intelligence and strong personality, dolphins behave unpredictably enough that scientists who study them are used to gleaning faint patterns amid messy data. But in this study, every mom changed its signature whistle around its calf in the same way. “The data are extraordinary and impressive,” Sabine Stoll, who studies language evolution at the University of Zurich, told me.

Dolphin baby talk isn’t exactly the same as ours—dolphin whistles don’t get more repetitive—but it’s certainly “the most convincing case of child-directed communication found in nonhuman animals to date,” Mirjam Knörnschild from the Museum of Natural History in Berlin, who led the study on sac-winged bats, told me. And its existence in a species separated from us by more than 90 million years of history is likely a “stunning” example of convergent evolution, Stoll said.

If both species evolved baby talk independently, perhaps they did so for similar reasons. Human parents can better grab their infants’ attention through high-pitched baby talk than through normal speech, and dolphin mothers might do the same. Keeping her signature whistle but raising its pitch “would be a pretty foolproof way for the mom to say ‘This whistle is meant for you’ to the calf, and for the calf to know My mom is talking to me right now and no one else,” Sayigh said. That specificity would allow both of them to keep close contact in a raucous ocean where many dolphins might be sounding off at once.

Human baby talk is also thought to strengthen a baby’s bond with its caregivers, and to help it learn language by exaggerating important features of the spoken word. The same could well apply to dolphins, which also stay with their mother for a long time, and learn calls by listening to their peers. But testing these ideas would be incredibly hard without separating mothers and their calves—an experiment that Sayigh said would cross an ethical line. She showed that dolphin baby talk exists; its exact role “is just one of those things that might have to go unanswered,” she said.