Factors Influencing the Prevalence and Handedness for Throwing in Captive Chimpanzees (Pan troglodytes).

Abstract

Humans throw right-handed, and it has been suggested that the neurophysiological demands of aimed throwing may have served as a precursor to the evolution of left hemisphere specialization for linguistic functions. Although there are descriptions of throwing by wild and captive chimpanzees (Pan troglodytes), systematic observations of aimed throwing and handedness have not been reported. In this article, evidence of population-level right-handedness for throwing is reported in 2 samples of captive chimpanzees. It is further reported that right-handed throwing is more pronounced than other measures of handedness in captive chimpanzees. The implications of these findings are discussed in the context of theories relating throwing to the evolution of lateralization for language functions.Hemispheric specialization refers to perceptual, motor, and cognitive processes that are differentially represented in the left and right cerebral hemispheres. Right-handedness and left hemisphere dominance for language functions are two of the most pronounced manifestations of hemispheric specialization in humans, and many researchers have suggested that these two traits are unique to hominid evolution (Corballis, 1992). Recent studies in a host of vertebrates have documented population-level behavioral and neuroanatomical asymmetries, indicating that language is not a necessary condition for the expression of hemispheric specialization, but rather that hemispheric specialization may be widespread in the animal kingdom (Rogers & Andrew, 2002).Less clear from the existing literature on hemispheric specialization in animals is how it relates to the evolution of right-handedness and left hemisphere dominance for language in humans. Some have suggested that right-handedness evolved in the context of increasing motor and cognitive demands associated with tool use (for review, see Bradshaw & Rogers, 1993) (Biro et al., 2003;Boesch, 1991;McGrew & Marchant, 1992 but see Hopkins, in press;Lonsdorf & Hopkins, 2005). Others have suggested that right-handedness evolved from extant left hemisphere lateralization for motor functions associated not with tool use but instead with vocalizations and possibly manual communicative functions (Corballis, 2002). In primates, there is little to no evidence of left hemisphere specialization in the production of vocalizations (Fernandez-Carriba, Loeches, Moricello, & Hopkins, 2002;Hauser, 1993; Hook-Costigan & Rogers, 1998), although there is evidence of population-level right-handedness for manual gestures (Hopkins, Russell, Freeman, et al., 2005). Thus, not all the assumptions of this theory are met from the extant literature.Calvin (1983) proposed that right-handedness and left hemisphere dominance for language evolved in the context of increasing neurophysiological, motor, and cognitive demands associated with throwing. Calvin argued from a neurophysiological standpoint that throwing requires that subjects acquire very precise timing windows with respect to the distance, movements, and traject...

The evolution and genetics of cerebral asymmetry

“…Palmer (2002) has suggested that the findings of Hopkins and colleagues may be due to statistical artefacts, and has shown the results to be marginal when assessed using funnel plots, which show scatter plots of righthand use against sample size, although the more recent studies do reveal significant species-level right-handedness using this technique (e.g. Hopkins et al 2005).…”

“…These estimates may not be truly indicative, however, since, within each species, hand preference does vary with task, and the tasks themselves are somewhat species-specific. One activity common to tests on both species is throwing, and the proportion of chimpanzees throwing with the right hand is higher than that for other measures (Hopkins et al 2005). In a sample of over a million humans in the USA, the incidence of right-handed throwing was 89.9 per cent for men and 92.4 per cent for women (Gilbert & Wysocki 1992), considerably higher than the values observed in a chimpanzee sample, where 53 animals were reported as right-handed, 16 as ambiguous and 23 as left-handed (Hopkins et al 2005).…”

“…Nevertheless, there is now some evidence for consistent handedness in other species. The work of Hopkins and colleagues has revealed a population-level preference for the right hand in captive chimpanzees, at least for certain activities such as extracting peanut butter from a glass tube (Hopkins 1996), using an anvil (Hopkins et al 2007), gestural communication (Hopkins & Leavens 1998) and throwing (Hopkins et al 2005).…”

The neural and cognitive correlates of aimed throwing in chimpanzees: a magnetic resonance image and behavioural study on a unique form of social tool use

“…Hopkins et al [4] have also found that posture influences handedness for throwing. Within the subsample of 89 chimpanzees that were observed to reliably throw by Hopkins et al [4], 90 per cent of right-handed individuals preferred to throw overhand compared with underhand. A majority of the overhand throws were made when the chimpanzees were standing bipedally.…”

“…Two previous studies have reported that captive chimpanzees show populationlevel right-handedness for throwing, which suggests left hemisphere dominance [4]. Hopkins et al [4] have also found that posture influences handedness for throwing. Within the subsample of 89 chimpanzees that were observed to reliably throw by Hopkins et al [4], 90 per cent of right-handed individuals preferred to throw overhand compared with underhand.…”