Hidden in the jungles of Sri Lanka is a small, but surprisingly charismatic monkey: the toque macaque. Endemic to the island, these feisty group-living monkeys are found nowhere else on earth.  And they are at the heart of a remarkable study - the longest primate research project ever undertaken.  For the last fifty years Dr Wolfgang Dittus has lived and worked among them, tracking their lives in his quest to understand how their complex society works.