The archaeological record has millions of human-made stone (lithic) remains dating from two and a half million years ago (Semaw 1997; Roche et al. 1999) to the present (Pétrequin and Pétrequin 2000). These include tools that were shaped intentionally to certain forms, such as Acheulean bifaces (Gowlett 1995, 1996, 2006), tools that were used for certain functions, such as Mousterian Levallois points (Moncel and Chacon-Navarro 2007), and the waste flakes left over from making (knapping) stone tools. Information about hand preference can be obtained from all of these categories. Lithic tool production, or stone knapping, can sometimes leave evidence in the form of flake scatters showing where and how the knapper sat (Wenban-Smith 1997). Tool-use can leave excellent traces of use-wear, which can reveal how the tool was held and the direction it moved during use (Longo and Skakun 2008). New work is underway on waste flakes, to extract hand preference information from specific fracture features related to the knapping posture and hand (Rugg and Mullane 2001; Uomini 2012; Bargalló and Mosquera 2013). Overall, the lithic data show that hominins were predominantly right-handed since before the common ancestor of modern humans and Neanderthals.

In addition to stone tools, bone tools and cave art leave clues about hand preference. Certain bones called retouchers were used to sharpen stone tools, and their diagonal marks can indicate the hand holding position (Rigaud 2007). In Palaeolithic cave art, thousands of handprints and hand stencils from around the world give us a direct image of prehistoric people’s hands from 36,000 years ago to the present. Hand prints were created by pressing a pigment-covered hand against a rock wall; the result is a “positive” hand. Hand stencils, or “negatives”, were created by placing the hand on the wall and spraying pigment around it (Fig. 6.3). These show a predominance of right-handers throughout the prehistory of our own species, Homo sapiens (Faurie and Raymond 2004).

The behaviour of extinct hominins can be encoded in their skeletons. As muscles grow and are used, they cause the bones to which they are attached to remodel themselves (Taaffe et al. 1994). Using one arm more than the other can thus cause one arm bone to become thicker and/or denser, as can be seen in professional tennis players (Ireland et al. 2013). Although prehistoric hominins probably did not play tennis, some did engage in activities which caused their upper limbs to become extremely asymmetrical (Stock et al. 2013). This is especially marked among Neanderthals, who show levels of asymmetry up to ten times those of even the most strenuous professional sports players of today (Trinkaus et al. 1994; Shaw et al. 2012; Shaw and Stock 2012). The activities that caused this asymmetry are not yet known, but some specialists have suggested the Neanderthals hunted large game (such as mammoths) by thrusting wooden spears (Churchill et al. 1996). The fossil arm bone evidence shows that most hominins with asymmetries had a right-sided bias, and only a few were left-sided (Tables 6.1, 6.2).

Another body of fossil evidence for hand preference is on the teeth. Certain hominin individuals have shallow cut-marks on their front teeth that were caused by a stone tool, were made throughout the individual’s lifetime, are distinct from dietary striations, are often clustered together, and are oriented diagonally. The orientation of these striations is currently used to infer the individual’s hand preference (Lozano et al. 2009; Frayer et al. 2012; Estalrrich and Rosas 2013). This is based on the hypothesis that the striations were caused by hominins doing a specific meat-eating activity, namely by holding large chunks or strips of meat in between the front teeth and cutting off bite-sized morsels with a sharp knife close to the lips (Semenov 1964). The striations are hypothesized to result from unintentional contact with the teeth, and to indicate the direction of cutting. While this hypothesis has been supported experimentally (Bermudez de Castro et al. 1988; Lozano et al. 2009), there are anecdotal reports of this activity among modern hunter-gatherers in the ethnographic literature (Uomini 2008). The fossil dental striations (Fig. 6.4) show that an asymmetrical action, favouring the right-handed pattern, was being carried out by many hominin individuals of H. erectus, H. heidelbergensis, and Neanderthals, including young children (Lozano et al. 2009).

Fossil asymmetries in the endocast add another piece of evidence to our lateralized ancestors. The combination of strong right frontal and left occipital petalias in the brain might be associated with right-handedness (Kertesz et al. 1990). These can be seen in endocasts of the genus Homo and Australopithecines. From the current sample of hominins with preserved endocasts, the majority show the right-handed pattern (Holloway and De La Coste-Lareymondie 1982; Balzeau et al. 2012a, b; Bruner and Pearson 2013). Other brain asymmetries can be seen in the endocast (Bruner et al. 2006; Poza-Rey and Arsuaga 2009, 2012). The functional significance of the asymmetries is not yet known, but Priddle and Crow (2013) have identified a gene pair called protocadherin 11X/Y which is unique to the human lineage in the last 6 million years and is the best candidate responsible for cerebral asymmetry and language (Williams et al. 2006). It is clear that only humans reach such an extreme level of brain asymmetry, even though great apes share some common features (Balzeau and Gilissen 2010; Smaers et al. 2011, 2013). For example, humans and chimpanzees both have high fluctuating asymmetry indicative of greater developmental plasticity, which suggests that hominin brains are more “evolvable” to follow selection pressures (Gómez-Robles et al. 2013). Structural asymmetries might or might not be related to functional asymmetries (Bradshaw 1988; Bruner and Manzi 2008; Bruner and Holloway 2010). What are some features of our brain’s functional lateralization that relate to prehistoric life?