Strangers do it, friends do it, politicians do it and so do chimpanzees: in fact, the handshake is so deeply embedded in our history and culture that it might even be older than humanity itself. So let's shake on it, and join palaeoanthropologist Ella Al-Shamahi as she embarks on a fascinating voyage of discovery through everything from evolutionary biology to the etiquette of modern life. Whether in ancient cave paintings or WHO guidelines, the handshake has helped us seal the deal, welcome a stranger and end conflict - as well as testifying to the enduring power of human contact.