Hand preferences for coordinated bimanual actions in 777 great apes: Implications for the evolution of handedness in Hominins

Abstract

Whether or not nonhuman primates exhibit population-level handedness remains a topic of considerable scientific debate. Here, we examined handedness for coordinated bimanual actions in a sample of 777 great apes including chimpanzees, bonobos, gorillas, and orangutans. We found population-level right-handedness in chimpanzees, bonobos and gorillas, but left-handedness in orangutans. Directional biases in handedness were consistent across independent samples of apes within each genus. We suggest that, contrary to previous claims, population-level handedness is evident in great apes but differs among species as a result of ecological adaptations associated with posture and locomotion. We further suggest that historical views of nonhuman primate handedness have been too anthropocentric, and we advocate for a larger evolutionary framework for the consideration of handedness and other aspects of hemispheric specialization among primates.

On the other hand: including left-handers in cognitive neuroscience and neurogenetics

“…Our closest living non-human relatives, the chimpanzees, also show a populationlevel bias towards right-handedness, although it is not nearly as marked as the roughly 9-to-1 ratio in humans 27 . Moreover, chimpanzees exhibit population-level asymmetries of some brain structures that are homologous to human brain structures that show asymmetry, including the planum temporale (a part of the temporal cerebral cortex that overlaps with Wernicke's classically defined language region) [28][29][30] .…”

The Many Sides of Hemispheric Asymmetry: A Selective Review and Outlook

“…Even population-level handedness seems to be widespread among primates. It is now well established that some 65 to 70% great apes favor the right hand in various tasks (e.g., Hopkins et al, 2011), although the incidence is lower than that in humans, which stands at around 90%. Orangutans seem to be an exception, with some 72% showing a left-hand preference in scratching and fine manipulation of the face, but no consistent asymmetry evident in other manual tasks (Rogers & Kaplan, 1996).…”

From action to language: comparative perspectives on primate tool use, gesture and the evolution of human language

“…This requires both semantic knowledge of individual tools' functions, and a generative set of rules for their effective use. Complex tool use typically also requires asymmetrical coordinated bimanual action (in which each hand plays a complementary role; [34]), which has been found to be the most reliable elicitor of population-level right-handedness in captive African apes [35]. Asymmetrical bimanual coordinated actions provide a context for hierarchical embedding, with the discrete but complementary actions of each hand needing to be described in a nested action syntax; while long sequences of such actions organized towards a larger goal also create long-range dependencies (where a preparatory action at one time step is meaningful only in relation with another action that is executed at a later time step).…”