Orangutans can use their voices like humans with their ability "greatly underestimated", according to new research.

Scientists say that studying the animals could hold the key to how human speech has evolved.

Researchers at the University of St Andrews and Indianapolis Zoo discovered the language similarities while studying great apes.

Rocky, 11, and Knobi, 36, two orangutans took part in the study by playing a basic musical instrument, like a kazoo, with complete freedom.

The scientists did the study at Indianapolis Zoo, working alongside animal care staff, where there is the largest group of orangutans in the United States.

Dr Adriano Lameira, of the School of Psychology and Neuroscience at St Andrews, led the research.

He said: "Language defines human communication but its evolution defies scientific explanation.

"Great apes, our closest relatives, may hold the key to how language evolved in our lineage.