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Global consistencies in infant-directed speech included higher pitch and increased pitch range. Other features that appeared many times in the recordings were contrasting vowels (like emphasizing a long “e” and a short “e” in the same word) and pulse clarity (using a musical voice). When the researchers analyzed singing, they noticed consistent changes in tempo and timbre.

The group trained a machine-learning model to use features like pitch and loudness to guess whether a recording was infant-directed or adult-directed. The model was largely accurate in its determination across the 21 societies and strengthened the case for global consistencies, according to Courtney Hilton, a postdoctoral fellow in the Department of Psychology and a co-first author on the paper.

“Our study provides the strongest test yet of whether there are acoustic regularities in infant-directed vocalizations across cultures,” Hilton said. “It is also really the first to convincingly address this question in both speech and song simultaneously. The consistencies in vocal features offer a really tantalizing clue for a link between infant-care practices and distinctive aspects of our human psychology relating to music and sociality.”

This research builds on earlier studies showing that lullabies and altered speech patterns can have a soothing effect on infants, as well as animal findings demonstrating the clear function of vocalizations such as sounding the alarm for an approaching predator or signaling friendliness and approachability.

“When we were selecting the features with which to look at infant-directed song and speech, we specifically appealed to some baseline bioacoustic principles that can be held constant not only in humans, but across different animals,” said Cody J. Moser, a co-first author on the paper, doctoral candidate at the University of California Merced, and a visiting student in Harvard’s Graduate School of Arts and Sciences. “Things about the way that we alter our pitch toward our infants might have their roots in ways that other animals communicate with each other.”

A secondary part of the study involved members of the public trying to identify whether a vocalization was infant-directed or adult-directed. More than 50,000 English speakers with fluency in 199 languages hailing from 187 countries participated in that portion of the study. Most were accurate in their assessments regardless of their native language or culture. This aspect of the research confirmed that people can pick up on the acoustic markers of infant-directed speech and song, even if they don’t understand the words or cultural references.

How people alter their voices when speaking to infants

Read the full study.

Mehr said this “citizen science” approach was invaluable to the researchers.

“The method we used for this paper — that allowed us to get 50,000 people to tell us if they thought a certain song was for a baby or for an adult — is the same method that we could use to understand the trajectory of music perception ability across a person’s lifespan, or whether people hear structure in music the same way depending on the type of language they speak,” he said. “The citizen science method is an innovation that many psychologists are excited about.”

The findings show striking parallels among cultures when it comes to talking and singing to infants, but Moser warned that the similarities shouldn’t be understood as truly universal features.

“We’re not trying to claim that all societies have infant-directed song or infant-directed speech, but we do now know that when people do tend to sing to their infants or speak to their infants, they tend to do it in the same way,” around the world, he said. “That is very interesting and a new finding.”

“There is, of course, a lot of variation and cultural influence in this practice, but we were also finding commonalities hinting at roots in our shared biology,” added Hilton. “In this study, we were trying to uncover these hidden parts of our minds that shape our everyday behavior and experiences.”

Researchers ran these results through mathematical simulations, which showed that this kind of genetic drift in the two groups could not have happened randomly and lead them to the conclusion that the cause was most likely the result of women not moving around to different islands as much as men.

“Females certainly moved to new islands, but when they did so they were part of joint movements of both females and males” said Reich. “This pattern of leaving the community must have been nearly unique to males in order to explain why genetic differentiation is so much higher in mitochondrial DNA than in the rest of the genome.”

The new study from an interdisciplinary team of geneticists and archaeologists quintuples the body of ancient DNA data from the vast Pacific region called Remote Oceania, the last habitable place on earth to be peopled. It also provides surprising insights into the extraordinarily complex peopling of one of Remote Oceania’s major subregions.

Humans arrived and spread through Australia, New Guinea, the Bismarck Archipelago, and the Solomon Islands beginning 50,000 years ago, but it wasn’t until after 3,500 years ago that they began living in Remote Oceania for the first time after developing the technology to cross open water in long-distance canoes.

This expansion included the region called Micronesia — about 2,000 small islands north of the equator, including Guam, the Marshall Islands, the Caroline Islands, Palau, and the Northern Mariana Islands.

It’s long been a mystery what routes people took to arrive in the region. The discovery that there were five streams of migration into Micronesia helps bring clarity to this mystery and the origins of the people there today.

“These migrations we document with ancient DNA are the key events shaping this region’s unique history,” said Liu, a postdoctoral fellow in Reich’s lab and the study’s lead author. “Some of the findings were very surprising.”

Of the five migrations, three were from East Asia, one from Polynesia, and one involved Papuans from the northern fringes of mainland New Guinea. This represented a new wrinkle for researchers because a prior stream of migration to the southwest Pacific and Central Micronesia came not from the mainland but New Britain, an island chain to the east of it.

The researchers also found that present-day Indigenous people of the Mariana Islands in Micronesia, including Guam and Saipan, derive nearly all their pre-European-contact ancestry from two of the East Asian-associated migrations the researchers detected. It makes them the “only people of the open Pacific who lack ancestry from the New Guinea region,” Liu said.

The researchers consulted with several Indigenous communities in Micronesia for the study. This is the Reich group’s fourth publication of original ancient DNA data from remote Pacific islands.

“It’s important that when we do ancient DNA work, we don’t just write a paper about the population history of a region and then move on,” Reich said. “Each paper raises as many new questions as it answers, and this requires long-term commitment to follow up the initial findings. In the Pacific islands there are so many open questions, so many surprises still to be discovered.”

Supporters for this study included the National Institutes of Health, the John Templeton Foundation, the Allen Discovery Center, and the Howard Hughes Medical Institute.

The Fitzpatrick Scale has been in the open domain for decades and was adopted by the tech industry primarily for use in machine learning and artificial intelligence. Humans must annotate images or videos to train machine-learning algorithms for things like face detections.

“Instead of using this Fitzpatrick Scale, which wasn’t designed to classify diverse skin tones among different groups of people, you would use the Monk Skin Tone Scale, which gives you a more granular understanding,” Monk said. He chose 10 color points to better represent the range of skin tones, opting out of wider range as a larger numbers would begin to create problems with annotation. Extensive fieldwork on skin tone and colorism in the U.S. and Brazil informed the final color selection.

Monk’s collaboration with Google began a few years ago when he was contacted by its Research Responsible AI team, and over time, the work turned to finding an alternative to the Fitzpatrick Scale, the sociologist said. That is when the team learned that Monk had developed a scale of his own.

Google is already using the Monk Skin Tone Scale in its image search. When users search makeup looks, for example, they can refine those searches by skin tone to find more relevant matches. The tech giant also used the scale to update its own Real Tone filters (an initiative it had already launched to deal with the skin-tone problem) on its Pixel cameras so that they can capture a wider, more realistic palette of shades.

“There’ve also been some refinements to search where people have complained that in the past, if you search for certain images, you only get back certain types of people,” Monk said. “One example is if you search for ‘cute babies,’ you might get a completely homogenous set of babies that basically all look white. That’s not a very inclusive experience for people at all.”

Google says the scale will be useful in checking the diversity of results for problems with algorithms. “This has been a longstanding issue, not just at Google, but across the tech industry,” Monk said.

Monk plans to publish research, testing the scale on a diverse group of people. He and the Google team conducted research together to validate the scale in the U.S., which was an extension of his own work.

Developers who do not intentionally design their products to work well across the continuum of skin tones will have products that do not work as well, Monk added. The new scale is open-source so that all companies around the world can make their products more inclusive.

“My hope is that other companies, not just Google, take on the work of auditing and making sure that their products are designed to work equally well across the entire range of skin tones, whether that’s using the Monk Skin Tone Scale or not,” Monk said. “I hope they do that work.”