If someone was to speak in so called "baby talk" you can be pretty sure it's to, well, a baby. Two studies, one in humans and one in rhesus monkeys, suggest that the tones mothers use to address babies are more universal than previously thought.
A group of researchers recorded English-speaking mothers saying the same sentences to babies and to adults. The recordings were then played to indigenous villagers in remote Ecuador.
Even though the villagers did not understand English, they could correctly identify whether the speaker was addressing a child or an adult 73% of the time.
A different team of scientists studied the role of certain high-pitched, melodic sounds called "girneys" and grunts in wild rhesus monkeys. Even though these calls were rarely produced before the birth season, once the first infants were born, the calls were used in abundance.
When infants wandered away from their mothers, other females kept a close eye on them and called with grunts and girneys as they watched them. In response, the infants looked back at the callers.
The observations suggest that these particular calls are directed at, and attractive to infants, rather than to other mothers. In that way, the grunts and girneys are similar to human "baby talk."