Handedness for manual gestures in great apes
Left hemisphere dominance for language and speech is a prominent feature of the human brain. Some have suggested that left hemisphere lateralization for language in modern humans evolved from an existing lateralized system for gestural communication in the common ancestor of humans and apes. Here, we conducted a meta-analysis of the data on handedness for manual gestures in great apes to test whether species-level asymmetries in hand use were evident and if these asymmetries were consistent across species. Hand preference data for manual gestures were summarized for published and unpublished data in the literature. For observational data, we found that bonobos, chimpanzees, gorillas and orangutans all showed group-level right handedness for manual gestures. For experimental data, group-level right handedness was only found for chimpanzees, though sample sizes were relatively small in the remaining ape species. When hand preference data were combined across ape species, we found that right handedness was much more prevalent for auditory gestures, such as clapping, compared to visual and tactile gestures. The results support the view that asymmetries in hand use for gestural communication was prevalent in the common ancestor of chimpanzees and humans and was possibly evident even earlier in primate evolution. Additional data are needed, particularly from wild apes to test for the presence of these asymmetries in subjects raised in their natural environment.