When did diplomacy start? Are there any examples of 'diplomacy' from pre-literary (prehistoric) age?

It is said that the diplomacy began when our predecessors first realized that it was better to hear the message than to eat the messenger. We are preparing a series of discussions on the topic of interplay between diplomacy and technology throughout history, so I wanted to ask if you know any interesting examples from prehistory that we can share with our audience - whether it is direct evidence (cave paintings, etc), or some indirect, anthropological evidence from the modern tribal practice.