It used to be thought that apes could only make noises that were tied to their emotions such as barks of alarm or hoots of excitement. But this strange peeping sound recorded from wild bonobos appears to have more in common with the calls of human babies.

At just three or four months of age, we humans let out growls or squeals that sound the same whether we are happy or distressed. It's up to our parents to figure out what we mean from the context.

The researchers say it's the same with these bonobos peeps. An identical sound is made in happy or in neutral contexts. So instead of being unique to humans, these flexible calls apparently date back at least six million years to our common ancestor with bonobos and chimpanzees. Dr Zanna Clay from the University of Birmingham said her key observation was that the bonobos separated the sound they were making from how they were feeling.

It seems that the flexibility of our own squawks and grunts joins the growing list of abilities that we humans can no longer count as uniquely ours.

Glossary 词汇表

barks 吼叫

hoots 叫喊

growls 低声的吼叫

squeals 长而尖的叫声

distressed 烦恼的，痛苦的

figure out 弄明白

context 环境，背景

common ancestor 共同的祖先

squawks (人)大声抱怨、喊叫

grunts (人因为不满或烦恼发出的)嘟哝，哼声
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