Learning to make sounds by listening to others is a skill that helps make us human.
But research now suggests a species of monkey may have evolved similar abilities.
Marmosets have the capacity to learn calls from their parents, according to research published Thursday in the journal Science. The results mean that studying marmosets might provide insights into developmental disorders found in humans. It also suggests that vocal learning may be more widespread than many researchers thought.
Many animals can link sounds with meaning. Dogs respond to simple calls; chimpanzees can even communicate with people using sign language. But the ability to hear a sound and mimic it is possessed by only a small number of species: primarily song birds and humans.
"We didn't think that mammals and primates in particular — besides us — had any type of vocal learning," says Asif Ghazanfar, a neuroscientist at Princeton University who led the new study.
Enter the small, adorable common marmoset. These fuzzy South American primates look more like squirrels than a monkey. "They're cute, and they smell. They wash themselves in their own urine," Ghazanfar says. "I'm not sure why they do that."
But once you get over the stink, these little guys are interesting. Marmoset mommies always give birth to twins and they need help rearing them. So, unlike many mammal species, fathers lend a hand, along with siblings and other community members.
Ghazanfar thinks all that child care is what gives marmosets another special trait: They're super talkative.
"They're chattering nonstop," he says. "That is also very different from our close relatives the chimpanzees."
Ghazanfar wanted to see if all that yammering was being taught from parents to babies. So, his group devised an experiment. The team took marmoset babies and separated them from their parents for short periods of time. Then researchers put the parents behind a barrier to see how the two would communicate.
They found that when parents responded to an infant's call with mature marmoset call, the infants learned the mature calls more quickly. In other words, the marmosets were learning vocalizations through imitation.
The work shows vocal learning is not "black and white," says Erich Jarvis, who studies vocal learning in birds at Duke University. He says that the traditional view has been that only a few animals are capable of vocal learning: "Humans and parrots are the haves, and non-human primates are the have-nots," he says.
Jarvis thinks the learning displayed by marmosets is much more primitive than what song birds and people can do. This new work suggests there's a continuum of learning to mimic sounds, Jarvis says.
Both researchers agree that studying marmosets could help humans. Because they're more closely related to our species than birds, they could provide special insights into developmental disorders involving communication, such as autism.
MELISSA BLOCK, HOST:
Robert, let's try a quick experiment here.
ROBERT SIEGEL, HOST:
BLOCK: See if you can make this mouth sound. (Making squeaky sound).
SIEGEL: That's easy for you to say.
SIEGEL: (Imitating squeaky sound). Not very well.
SIEGEL: E for effort, Robert. Well, it turns out that imitating sounds is something that humans are really good at. It's part of what makes us special. And NPR's Geoff Brumfiel reports that researchers now think a species of monkey might possess similar skills.
GEOFF BRUMFIEL, BYLINE: Learning to make sounds by listening to others is called vocal learning, and there's just a few species that can do it - mostly birds and humans. Now, don't get me wrong, chimpanzees are smart. They can learn some sign language, but they can't learn to talk.
ASIF GHAZANFAR: We didn't think that mammals - and primates in particular - besides us actually had any type of vocal learning.
BRUMFIEL: Asif Ghazanfar is at Princeton University. Now research he's published in the journal Science suggests there's at least one species of monkey that might be able to learn vocally, the common marmoset. Marmosets aren't your typical primate. They're tiny with big, round eyes and long, fluffy tails.
GHAZANFAR: They're cute and they smell. They wash themselves in their own urine. I'm not sure why they do that.
BRUMFIEL: But Ghazanfar says once you get over the smell, these little guys are interesting. Marmoset mommies always give birth to twins and they need help raising them, so everyone gets involved.
GHAZANFAR: The father sticks around and helps take care of the offspring. Moreover, older siblings will help take care of younger siblings and group members that are unrelated to those infants will also help out.
BRUMFIEL: Sound familiar? That's how humans do it. Ghazanfar thinks all the child care is what gives marmosets another special trait - they're super talkative.
(SOUNDBITE OF MARMOSET CHIRPING)
GHAZANFAR: They're chattering nonstop, and that is also very different from our close relatives, the chimpanzees.
BRUMFIEL: To see if all that yammering was passed on from parents to babies, Ghazanfar devised an experiment.
GHAZANFAR: Almost every other day, we simply took one of the infant marmosets, and for a very brief time, we separated it from its parents and then recorded its vocalizations.
(SOUNDBITE OF MARMOSET INFANT CHIRPING)
BRUMFIEL: The very young infants made low, raspy sounds - not your typical marmoset chatter.
GHAZANFAR: It kind of has this rough, noisy characteristic to it.
BRUMFIEL: But over time, that changed.
GHAZANFAR: When they reach about two months of age then they're going to produce these very kind of clear, whistle-like calls.
(SOUNDBITE OF MARMOSET CHIRPING)
GHAZANFAR: They really are annoying, unfortunately.
BRUMFIEL: The amount of time it took to go from the low, rough call to that high squeak depended on how much feedback the baby marmosets were getting from their parents. In other words, the marmosets were learning through listening, vocal learning.
Erich Jarvis studies vocal learning in birds like parrots at Duke University. He says there's been a long-held view in science that when it comes to learning how to imitate sounds...
ERICH JARVIS: You have it and you don't have it. And humans and parrots are the haves and nonhuman primates are the have-nots.
BRUMFIEL: This new work shows that's probably not the case. The marmosets are able to pick stuff up, though Jarvis still isn't convinced that this learning is as complex as what humans and birds can do.
JARVIS: There is something in between, all right? Not necessarily black and white, but a continuum.
BRUMFIEL: Both researchers agree that studying marmosets could be useful for us humans. Because we're both social primates, these little monkeys might be able to provide clues about human disorders that make learning language difficult. Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.