Handedness

The question of whether non-human primates show population-level handedness remains a topic of significant debate.   Studies in captive chimpanzees with relatively large numbers of subjects (N > 200 or 300) have shown that certain tasks can elicit population-level biases such as throwing, manual gestures and tasks that require bimanual coordination (Hopkins et al, 2010, 2011; Llorente et al. 2010).   More recently, studies from wild chimpanzees and to a lesser extent gorillas have reported evidence of group level asymmeteries in hand use for some forms of tool use (wadge dipping, termite fishing, ant dipping, bimanual feeding) Notwithstanding, the ratio of right-to-left handed individuals (or vice versa) in the studies of chimpanzees is much lower (2:1 or at best 3:1) than what has been reported in humans (typically 8:1 or 9:1).   What mechanisms explain these differences is unlcear but both genetic and non-genetic factors have been proposed.  There is a definite need for further studies, particulary in different communities of wild apes in which common measures can be obtained.