Laterality in Maternal Cradling and Infant Positional Biases: Implications for the Development and Evolution of Hand Preferences in Nonhuman Primates

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

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, non-genetic 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.

Left Nipple Preferences in Infant Pan paniscus and P. troglodytes

We investigated laterality in nipple preference in 16 mother-infant dyads, 8 bonobos, and 8 chimpanzees via an event sampling procedure in infants 5-55 mo of age. Both bonobo and chimpanzee infants preferred the left nipple, and the results were stable over time. Maternal age, experience, and rearing history did not influence laterality in offspring nipple preferences. We discuss the results in the context of the role of early mother-infant interactions on the development of laterality in primates.

Comparative and familial analysis of handedness in great apes

Historically, population-level handedness has been considered a hallmark of human evolution. Whether nonhuman primates exhibit population-level handedness remains a topic of considerable debate. This paper summarizes published data on handedness in great apes. Comparative analysis indicated that chimpanzees and bonobos show population-level right handedness, whereas gorillas and orangutans do not. All ape species showed evidence of population-level handedness when considering specific tasks. Familial analyses in chimpanzees indicated that offspring and maternal (but not paternal) handedness was significantly positively correlated, but this finding was contingent upon the classification criteria used to evaluate hand preference. Overall, the proportion of right handedness is lower in great apes compared with humans, and various methodological and theoretical explanations for this discrepancy are discussed.

Behavioural lateralisation in the Australian magpie (Gymnorhina tibicen)

In many vertebrates, the brain is lateralised such that each hemisphere is specialised to serve specific functions. This may translate into lateralisation in behaviour through preferential use of receptors or appendages associated with a particular hemisphere (e.g., handedness) or in differential responses to stimuli perceived on the animal's left or right side. In this study, we investigated behavioural laterality in the Australian magpie, Gymnorhina tibicen. We found that, while the birds did not have a population bias for one antipredator behaviour (visual inspection of an approaching human), there were biases for another (alarm calling); those birds that used their left eye more relative to their right eye gave alarm calls more frequently. We also observed that juvenile birds begged for food on the right side of parents significantly more frequently than on the left side. These trends are consistent with trends in behavioural laterality that have been recorded in captive and lab-reared species. Ours is one of the few studies to observe patterns of laterality in a wild species.

The distribution and development of handedness for manual gestures in captive chimpanzees (Pan troglodytes)

This article describes the distribution and development of handedness for manual gestures in captive chimpanzees. Data on handedness for unimanual gestures were collected in a sample of 227 captive chimpanzees. Handedness for these gestures was compared with handedness for three other measures of hand use: tool use, reaching, and coordinated bimanual actions. Chimpanzees were significantly more right-handed for gestures than for all other measures of hand use. Hand use for simple reaching at 3 to 4 years of age predicted hand use for gestures 10 years later. Use of the right hand for gestures was significantly higher when gestures were accompanied by a vocalization than when they were not. The collective results suggest that left-hemisphere specialization for language may have evolved initially from asymmetries in manual gestures in the common ancestor of chimpanzees and humans, rather than from hand use associated with other, non-communicative motor actions, including tool use and coordinated bimanual actions, as has been previously suggested in the literature.

Wild chimpanzees show population-level handedness for tool use

Whether nonhuman primates exhibit population-level handedness remains a topic of considerable theoretical and empirical debate. One continued subject of discussion is whether evidence of population-level handedness in primates is confined to studies in captive animals or whether it is in both captive and wild subjects. Here, we report evidence of population-level handedness in wild chimpanzees for a tool-use task known as "termite-fishing." We subsequently compared the handedness for termite-fishing with other published reports on handedness for nut-cracking and wadge-dipping and found task-specific differences in handedness. Last, when combing all of the published data on tool use in wild chimpanzees, we show that hand preferences are heritable. Contrary to previous claims, our results demonstrate that population-level handedness is evident in wild chimpanzees and suggest that the antecedents of lateralization of function associated with hand use were present at least 5 million years ago, before the Pan-Homo split.