The quest to understand what makes us humans began with the search for the ‘missing link’, that enigmatic fossilised hominid that was thought would bridge the gap between ‘them’, the non-human primates, and us. In more recent times the picture growing from this quest looks more like a chain-link fence, than the envisioned simple link idea, with each passing discovery bringing new examples of extinct species sharing a mosaic of traits shared by humans and great apes (e.g. Templeton, 2005; White, 2012). With the pioneering great ape studies in the 1960s and 1970s, the search began to incorporate studies on our closest living relatives, the great apes, species with which we share many obvious behavioural, physiological and anatomical traits. Over the years primatology has methodically removed the perceived barrier between humans and apes, with the discovery of such behaviours as tool use, tool making and hunting with or without tools, communication, conspecific warfare, even the possible use of medicinal plants to treat illness (e.g. Goodall, 1968, 1986; McGrew, 1979, 1981, 1992; Boesch and Boesch, 1981; Nishida et al., 1985; Huffman and Seifu, 1989; Huffman and Kalunde, 1993; Boesch, 1994; Van Schaik and Knott, 2001; Van Schaik et al., 2003; Mitani et al., 2010). For some, this may seem like the beginning and the end point for looking at the origins of characteristics considered unique to humans. But is it really?

As our discipline advances, the boundaries have been pushed even further, with studies promoting macaques and capuchins as suitable models for human evolution of tool use behaviour, through the discovery of their ability to use stone tools as deftly as chimpanzees (e.g. Fragaszy et al., 2004; Moura and Lee, 2004; Ottoni and Izar, 2008; Gumert et al., 2009, 2011; Visalberghi et al., 2009). In this context, behavioural innovation and the long-term maintenance of stone handling, a non-functional cultural behaviour in macaques, and the artefacts of this behaviour left behind provide thought for socioecological forces behind the emergence of tool use in early humans (Huffman and Quiatt, 1986; Quiatt and Huffman, 1993; Huffman et al., 2010). Clearly, the gap between apes and monkeys is not as large as was once thought.