Orang-utans know how to give and take favours...

Orangutans can help each other get food by trading tokens, scientists have discovered - but only if the help goes in both directions. 

Researchers from the University of St Andrews found orangutans could learn the value of tokens and trade them, helping each other win bananas. 

An article in Biology Letters, claims it is the first evidence of "calculated reciprocity" in non-human primates. More...

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