Chimpanzees (Pan troglodytes) Are Predominantly Right-Handed: Replication in Three Populations of Apes.

Russell²,

Schaeffer³

2012

Phil. Trans. R. Soc. B

Self Cite

It has been hypothesized that neurological adaptations associated with evolutionary selection for throwing may have served as a precursor for the emergence of language and speech in early hominins. Although there are reports of individual differences in aimed throwing in wild and captive apes, to date there has not been a single study that has examined the potential neuroanatomical correlates of this very unique tool-use behaviour in non-human primates. In this study, we examined whether differences in the ratio of white (WM) to grey matter (GM) were evident in the homologue to Broca's area as well as the motor-hand area of the precentral gyrus (termed the KNOB) in chimpanzees that reliably throw compared with those that do not. We found that the proportion of WM in Broca's homologue and the KNOB was significantly higher in subjects that reliably throw compared with those that do not. We further found that asymmetries in WM within both brain regions were larger in the hemisphere contralateral to the chimpanzee's preferred throwing hand. We also found that chimpanzees that reliably throw show significantly better communication abilities than chimpanzees that do not. These results suggest that chimpanzees that have learned to throw have developed greater cortical connectivity between primary motor cortex and the Broca's area homologue. It is suggested that during hominin evolution, after the split between the lines leading to chimpanzees and humans, there was intense selection on increased motor skills associated with throwing and that this potentially formed the foundation for left hemisphere specialization associated with language and speech found in modern humans.

Section: Discussionmentioning

confidence: 99%

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

Russell²,

Schaeffer³

2012

Phil. Trans. R. Soc. B

Self Cite

“…A minimum of 20 responses were recorded from each subject. Although other measures of hand preference have been collected in these chimpanzees (Hopkins, Wesley, Izard, Hook, & Schapiro, 2004), the TUBE measure was used to classify subjects as left-or right-handed because: (a) it induces individual hand preferences in more than 85% of the chimpanzees; and (b) it is a highly reliable measure with test-retest measures exceeding 0.70 over a 2-year period (Hopkins, 2006).…”

Section: Methodsmentioning

confidence: 99%

Parental and perinatal factors influencing the development of handedness in captive chimpanzees

Developmental Psychobiology

Wesley

Russell

et al. 2006

Self Cite

It has been proposed that human right handedness is determined by genetic factors associated with the emergence of language, whereas non-human primate handedness is determined by random, nongenetic factors. These different mechanisms account for differences in the distribution of handedness between human and non-human primates. Here we report evidence that genetic factors play a role in the determination of handedness in chimpanzees. We further report that differential rearing has no influence on the expression of handedness in related individuals. Contrary to many theories of the origin of handedness, these results indicate that genetic factors have a significant influence on handedness in chimpanzees.

“…Most observations were made while subjects were in the outdoor portions of their home cages. At Yerkes and UTMDACC, the chimpanzees are housed in either pairs, small social groups of 3 to 12 individuals, or larger groups (13 to 22 individuals) living in compounds (for a description of housing conditions, see Hopkins, Wesley, Izard, Hook, & Schapiro, 2004).Although the social context was not recorded for each throwing event observed here, in our extensive experience with captive chimpanzees, we have observed that they throw substrates in three social contexts. First, the chimpanzees are often observed to throw at unfamiliar humans who are in proximity or approaching their home cages.…”

mentioning

confidence: 97%

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

Journal of Comparative Psychology

Russell

Cantalupo

et al. 2005

Self Cite

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...