Monkeys Understand Language Musicality Rules: Evolution of Human Speech

Language is a part of what makes us human, but learning different languages can often be a difficult process. There are rules and patterns in a language that make something "sound good" or cause it to become almost intelligible. Now, scientists have found that these structural and melodic patterns in languages are so simple, even monkeys can understand them.

Both language and music are structured systems. They feature particular relationships between syllables, words and musical notes. For example, implicit knowledge of the musical and grammatical patterns of our language makes us notice right away whether a speaker is a native or not. In a similar way, the perceived musicality of some languages results from dependency relations between vowels within a word.

Similar "dependencies" within words can be found in languages around the world. In order to see whether or not the ability to process these dependencies was a uniquely human feature, though, researchers turned to South American squirrel monkeys. Inspired by the monkey's natural calls and hearing predispositions, the scientists designed a type of "musical system" for monkeys. These musical patterns had overall acoustic features similar to monkeys' calls, while their structural features mimicked syntactic or phonological patterns like those found in human languages.

The monkeys were presented with phrases that contained structural dependencies. They were later tested using stimuli either with or without dependencies. Their reactions were then measured. In the end, the scientists found that the monkeys reacted more to "ungrammatical" patterns, which demonstrated the perception of dependencies.

"Our ancestors may have already acquired this simple dependency-detection ability some 30 million years ago, and modern humans would thus share it with many other living primates," said Andrew Ravignani, one of the researchers, in a news release. "Mastering basic phonological patterns and syntactic rules is not an issue for squirrel monkeys: the bar for human uniqueness has to be raised. This is only a tiny step: we will keep working hard to unveil the evolutionary origins and potential connections between language and music."

The findings reveal a little bit more about human evolution. More specifically, they show that our ability to recognize patterns isn't an inherently human ability. This, in turn, shows the evolutionary origins of human speech.

The findings are published in the journal Biology Letters.