This paper explores how three central figures in the field of British prehistory – Sir Arthur Keith, Sir Grafton Elliot Smith and Louis Leakey – deployed different disciplinary practices and narrative devices in the popular accounts of human bio-cultural evolution that they produced during the early decades of the twentieth century. It shows how they used a variety of strategies, ranging from virtual witness through personal testimony to tactile demonstration, to ground their authority to interpret the increasingly wide range of fossil material available and to answer the bewildering variety of questions that could be asked about them. It investigates the way in which they positioned their own professional expertise in relation to fossil interpretation, particularly with regard to the – sometimes controversial – use they made of concepts, evidence and practices drawn from other disciplines. In doing so, they made claims that went beyond their original disciplinary boundaries. The paper argues that while none of these writers were able, ultimately, to support the wider claims they made regarding human prehistory, the nature of these claims deserves much closer attention, particularly with respect to the public role that historians of science can and should play in relation to present-day calls for greater interdisciplinarity.