Abstract
A number of factors have been proposed to influence within and between species variation in handedness in non-human primates. In the initial study, we assessed the influence of grip morphology on hand use for simple reaching in a sample of 564 great apes including 49 orangutans Pongo pygmaeus, 66 gorillas Gorilla gorilla, 354 chimpanzees Pan troglodytes and 95 bonobos Pan paniscus. Overall, we found a significant right hand bias for reaching. We also found a significant effect of the grip morphology of hand use. Grasping with the thumb and index finger was more prevalent in the right compared to left hand in all four species. There was no significant sex effect on the patterns of handedness. In a subsample of apes, we also compared consistency in hand use for simple reaching with previously published data on a task that measures handedness for bimanual actions. We found that the ratio of subjects with consistent right compared to left hand use was more prevalent in bonobos, chimpanzees and gorillas but not orangutans. However, for all species, the proportion of subjects with inconsistent hand preferences between the tasks was relatively high suggesting some measures may be more sensitive in assessing handedness than others.
Highlights
All human populations have been shown to exhibit a predominance of right-handedness (Perelle and Ehrman, 1994; Abell et al, 1999; Annett, 2002; Raymond and Pontier, 2004), for complex motor actions (Marchant et al, 1995; Fagard and Marks, 2000)
In the non-human primate literature, the collective studies on handedness reveal divergent patterns of hand preference within and between the species and show large variability concerning the method of data collection, sample size, environment of the subjects, ecology of the species, and the manual tasks used for assessing hand preferences
This study revealed that lateralized hand use for grasping was associated to contralateral brain asymmetries in the white matter of the motor hand area of the precentral gyrus (Hopkins et al, 2010), an anatomical correlate which overlaped with PET brain activation in this region
Summary
All human populations have been shown to exhibit a predominance of right-handedness (Perelle and Ehrman, 1994; Abell et al, 1999; Annett, 2002; Raymond and Pontier, 2004), for complex motor actions (Marchant et al, 1995; Fagard and Marks, 2000). There is a large body of evidence of the effect of the task complexity on the direction, magnitude and consistency of the individual hand preferences in humans (Perelle and Ehrman, 1994; Marchant et al, 1995; Fagard, 2001), great apes (Boesch, 1991; O’Malley and McGrew, 2006; Humle and Matsuzawa, 2009; Bogart et al, 2012), and monkeys (Fagot and Vauclair, 1988, 1991; Fagot et al, 1991; Spinozzi et al, 1998; Blois-Heulin et al, 2006; Lilak and Phillips, 2007; Meunier and Vauclair, 2007; Schweitzer et al, 2007) In most of these studies, the distinction between unimanual reaching actions and bimanual coordinated behaviors has been critical for the task complexity’s effects on individual hand preferences and for revealing population-level handedness. These results indicate that complex bimanual actions appear to be more sensitive for detecting hand preferences than unimanual tasks, such as unimanual reaching
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