Indeed, Hopkins et al. (2002) and Westergaard et al. (1997) tested the hand preference

using a lower number of tasks. Concerning the different results obtained from human subjects and monkeys, several find more explanations appear pertinent. Sociability plays an important role for the handedness (Hopkins 2006). Indeed, pedagogical or cultural pressures can influence the hand preference in humans, which is not considered to be the case in nonhuman primates. The postural origin theory of handedness offers a possible explanation for the monkey data (MacNeilage et al. 1987). Indeed, several studies showed a right-hand preference for more terrestrial species, whereas Inhibitors,research,lifescience,medical a left-hand preference was found for more arboreal animals (Masataka 1989; Singer and Schwibbe 1999; Hopkins et al. 2011; Meguerditchian et al. 2012; Zhao et al. 2012). In our case, our animal model, the M. fascicularis, is considered to be both arboreal and terrestrial (Fooden 2006; South Asian Primate C.A.M.P. Report, 2003; http://www.zooreach.org/downloads/ZOO_CAMP_PHVA_reports/2003%20Primate%20Report.pdf). Our results in M. fascicularis monkeys, Inhibitors,research,lifescience,medical showing a right- or left-hand preference depending on the tasks, is thus Inhibitors,research,lifescience,medical in line with the postural origin theory, in the sense that our animals did not show a clear right- or left-handedness, but an intermediate and

variable position, consistent with the mixed arboreal and terrestrial status of M. fascicularis. These data are consistent with hand preference observations derived from simple food reaching task, also in cynomolgus (M.

fascicularis) monkeys (Lehman 1980b). In a longitudinal Inhibitors,research,lifescience,medical study (from birth to weaning) conducted on a large number of monkeys (M. fascicularis), and based also on a task using a slot board but emphasizing more the attribute of hand dominance than hand preference (Brinkman and Smithson 2007), it was found that the infant monkeys showed a “dominant” hand at individual level (but bimodal distribution at population level). Their hand “dominance” was the same as that of their mother and, moreover, their pattern of grip movement resembled their mothers’, suggesting imitation Inhibitors,research,lifescience,medical (Brinkman and Smithson 2007). In line with Hopkins (2004), the present data in M. fascicularis show that, as far as hand preference is concerned, they considerably diverge from human subjects (highly lateralized), whereas apes can be placed in between the two groups, with intermediate hand preference oxyclozanide characteristics. This wide range of behavioral lateralization is consistent with its multifactorial origin (see e.g., Rogers 2009; Schaafsma et al. 2009; Uomini 2009; Forrester et al. 2013). Acknowledgments The authors wish to thank the technical assistance of Josef Corpataux, Laurent Bossy and Jacques Maillard (animal house keeping), André Gaillard (mechanics), Bernard Aebischer (electronics), Laurent Monney (informatics). This study was supported by Swiss National Science Foundation, grants No. 31-61857.00, 310000-110005, 31003A-132465, and FZFS-0_144990 (E.