A colony of adult bushbabies was assessed for hand preference in order to determine what the proportion of preference for the left and right might be for the population and whether hand preference for individuals was reliable. 25 animals were tested in an apparatus demanding a vertical stance. The population bias was expressed in a distribution skewed toward a left-hand bias. With 16 animals available for retesting, the test-retest reliability coefficient was 0.651, significant at the 0.01 level. When 12 of the original subjects were tested in an apparatus demanding a quadrupedal stance, hand preference shifted to a bimodal distribution. Test-retest reliability was 0.864, significant at the 0.01 level. Significant correlations were not found between the two types of test nor between the two retests. Neither sex nor length of laboratory residence served to predict hand preference. These results were discussed with the view that the postural adjustments required by a bipedal stance may have shaped the development of handedness in humans.

A population of 194 lemurs (Lemur spp.), 116 males and 78 females, from 1 to 30 years of age, was assessed for lateralized hand use in simple food reaching with a minimum of 100 reaches per animal. A hand preference was present in 80% of the population with a bias for use of the left hand that was most characteristic of male lemurs and young lemurs. The results confirm the presence of lateralization in prosimians, and we interpret the sex and age differences in relation to current theories of neural lateralization.

Behavioral laterality was studied in a captive group of 11 bonobos (Pan paniscus). In an observational method a significant left lateral bias in carrying and a right lateral bias in leading limb were found. Direction of lateral bias in carrying and leading limb was enhanced when subjects maintained a bipedal posture. Analysis of bimanual feeding behavior revealed a significant right-hand bias for eating when subjects were holding food with their left hand. In an experimental method a significant shift toward greater right-hand use was found when subjects were required to maintain a bipedal, rather than a quadrupedal, posture. There was no evidence of lateral bias for measures of face touching, self-touching, or gestures. The results are discussed in the context of previous reports of primate laterality.

Lateral preferences in food reaching and whole-body turning were assessed in 24 prosimian primates: 16 galagos (Galago moholi) and 8 mouse lemurs (Microcebus murinus). Reach and turn preference in the galago were examined using a single testing procedure; separate procedures were used to evaluate reach and turn preferences in the mouse lemur. The motoric requirements for both species were 1) reach into a Plexiglas container with a single hand for a food item and 2) execution of a whole-body rotation about the long axis of the body. Twenty-three of the subjects tested had a reach preference (15 right, 8 left preferent) and 22 a turn preference (1 right and 21 left preferent). No correlation between the direction of reach and turn preference was found for either species; however an association between right reach preference and female gender was found for the galagos. A species difference in the strength of lateralization was found, with the more bipedal species, the galago, more strongly lateralized in both measures. This result supports the hypothesis that the assumption of upright posture was an important factor in the phylogenetic development of primate lateralization.

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