The research team analyzed voice tones of two groups of the same species of primates, the Japanese Yakushima macaque also known as Macaca fuscata yakui, between 1990 and 2000.

The result showed that the island group had a tone about 110 hertz higher on average than the one taken to central Japan.

Monkeys on Yakushima Island have an accent with a higher tone because tall trees on the island tend to block their voice, Masataka said.

"On the other hand, monkeys on Mount Ohira do not have to gibber with a high tone as trees there are low," he said. "Each group adopted their own accent depending upon their environment." This suggests differences in voice tones are not caused by genes, Masataka said, adding the results "may lead to a clue to the origin of human language.