Monkeys did sing like humans once

Ancient monkeys used auditory cues similar to humans to distinguish between low and high sound notes, say researchers, adding that pitch perception may have evolved more than 40 million years ago to enable vocal communication and song-like vocalisations.

Pitch perception is essential to our ability to communicate and make music.

"But until now, we didn't think any animal species, including monkeys, perceived it the way we do. Now we know that marmosets, and likely other primate ancestors, do," said Xiaoqin Wang, professor of biomedical engineering at Johns Hopkins University's school of medicine.

Marmosets are small monkeys native to South America that are highly vocal and social.

Other animal species have been reported to show pitch perception but none have shown the three specialised features of human pitch perception.

First, people are better at distinguishing pitch differences at low frequencies than high.

Second, humans are able to pick up on subtle changes in the spread between pitches at low frequencies or hertz.

And third, at high frequencies, peoples' ability to perceive pitch differences among tones played simultaneously is related to how sensitive they are to the rhythm.

Through a series of hearing tests, Wang's team determined that marmosets share all three features with humans, suggesting that human components of pitch perception evolved much earlier than previously thought.

The American continent, with its marmosets in place, broke away from the African land mass approximately 40 million years ago, before humans appeared in Africa.

So it's possible that this human-like pitch perception evolved before that break and was maintained throughout primate evolution in Africa until it was inherited by modern humans.

"Another possibility is that only certain aspects of pitch perception were in place before the split, with the rest of the mechanisms evolving in parallel in Old and New World monkeys," the authors noted.

"Now we can explore questions about what goes wrong in people who are tone deaf and whether perfect pitch is an inherited or learned trait," Wang concluded in a paper forthcoming in the journal Proceedings of the National Academy of Sciences.