Towards a Prehistory of Primates

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The social and technological traits of living non-human primates (henceforth 'primates') have contributed significantly to reconstructions of the activities of their past common ancestors with humans (van Schaik et al. 2003; Haslam et al. 2009; McGrew 2010; Silk 2011; Whiten 2011; Wynn et al. 2011). Customary tool-use by wild primates, a key trait of interest to archaeologists, has been recorded in tropical Africa, South America and Southeast Asia, including by chimpanzees (Figure 1), orangutans and bearded capuchin monkeys (McGrew 1992; van Schaik et al. 1996; Spagnoletti et al. 2011). Less well studied or less prevalent wild tool-use has also been noted among gorillas, bonobos, long-tailed macaques and both yellow-breasted and blonde capuchins (Hohmann & Fruth 2003; Breuer et al. 2005; Malaivijimond et al. 2007; Canale et al. 2009; Souto et al. 2011). Yet there is a great disparity in the observational time span for human and primate behaviour, because the archaeological record of hominins (human ancestors back to our split with the Pan lineage) has unusual chronological depth.

At present, hominin technical activities have been detected back ~3.4 million years (McPherron et al. 2010), with a well-studied and possibly continuous stone tool record since 2.6 million years ago (mya) (Semaw et al. 2003). This record is augmented by non-stone prehistoric technologies for tens, and in some cases hundreds, of thousands of years (e.g. Thieme 1997). In contrast, we have around half a century of systematic chimpanzee behavioural data, and even less for other primates, although anecdotal reports from West Africa extend back around 400 years (Sept & Brooks 1994). When extinct hominin behaviours are compared with those of living primates (e.g. Joulian 1996; Gowlett 2009; Pruetz & Bertolani 2009; Toth & Schick 2009; de la Torte 2010; Ungar & Sponheimer 2011), we need to ask whether extant primate behaviour is representative of the several million years of behavioural evolution that preceded it. In other words, when did apes, monkeys and other primates become 'behaviourally modern', and how would a more complete primate archaeological record change our perspective on human evolution?


Behavioural modernity

Significant behavioural changes have occurred in the hominin lineage during the past few million years, and archaeologists studying Homo sapiens have concentrated on the issue of 'behavioural modernity' (Minugh-Purvis 1995; McBrearty & Brooks 2000; Wadley 2001; d'Errico 2003; Henshilwood & Marean 2003; Renfrew 2007; Conard 2008). At the core of this concept is a search for features that are unique to our species, an attempt to identify the process by which the habits and capacities of past humans came to be recognisably similar to those of humans living today (Klein 2000). While this may be a useful driver of debate (d'Errico & Stringer 2011; Shea 2011), the proposal of a radical behavioural shift, or 'human revolution' (Mellars & Stringer 1989; Bar-Yosef 2002) part way through hominin evolution is unusual when placed in a broader zoological context. There is, for example, no literature on the timing and character of the emergence of 'modern Macaca behaviour', or international conferences discussing a possible 'Papio behavioural revolution'.

From the mid twentieth century onwards, the combination of increasing numbers of hominin fossil discoveries and the establishment of long-term field primatology sites opened up new debates over the similarities between hominins and other African primates (e.g. Leakey 1961; Washburn & DeVore 1961; Holloway 1969; Jolly 1970; Foley 1987). Archaeologists explored the ways that the emerging primate literature could inform topics such as early Pleistocene site creation and social structure (Clark 1960; Isaac 1969), but it was modern, twentieth-century primates that were the point of comparison. …