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.

Evaluated a free-ranging matriline of 13 ring-tailed lemurs (Lemur catta) from videotaped records for lateralized hand use with 2 tasks and 4 measures: food reaching, feeding posture, duration of food holding, and manipulation of food between mouth and hand while eating. Binomial z scores determined 7 lemurs to be left preferent in reaching, 3 right, and 3 ambipreferent. Ideographic analyses suggested possible sex-linked and early experience twin effects. When compared to right and ambipreferent lemurs, left reach preferent lemurs used the left hand more but bimanuals grasped less in food holding and also engaged in less hand-mouth food manipulation. The tendency to manipulate food was not correlated with bimanual holding but was inversely related to left hand holding and directly related to right hand holding. These patterns are discussed as possible precursors of human bimanual manipulation.

The hand preferences of 5 semi-free-ranging black-and-white ruffed lemurs were assessed by using three distinct testing procedures. Testing conditions varied in the extent to which they required animals to make a whole body postural adjustment prior to making a reach. Minimal bodily adjustment was necessary for free foraging, whereas discrete food presentations on land (DFP-land) and in a moat (DFP-moat) promoted a gross reorientation of the animal's entire body. In the DFP-moat condition 4 animals exhibited exclusive use of the left hand, and only 1 of 515 reaches was made with the right hand. Similarly, all 5 animals showed a pronounced left hand preference in the DFP-land condition. The free-foraging condition revealed a hand preference for only 1 of the 5 subjects, and that preference was weak in comparison with those measured in the other two test conditions. These findings indicate that whole body postural adjustments critically influenced the expression of hand preference and should be taken into consideration in future studies of primate hand preferences.

ABSTRACT. The present study assessed the hand preferences exhibited by 33 black lemurs during routine feeding. Individual animals displayed hand preferences that were consistent across observations separated by as much as seven months. Within this population, 20 were left hand preferent, 12 right preferent, and 1 was ambidextrous. Correlational analysis of age and percentage left hand use indicated an inverse relationship in which younger animals tended towards the preferential use of the left hand and older animals the preferential use of the right hand. Similar analysis found no relationship between either sex and hand preference or familial relationship and hand preference. The skewed distribution of age in this sample renders tentative conclusions regarding age-related variations in hand preference. It is suggested that if the hand preferences of the black lemur are not age-related, then this species may be characterized as having a bias towards the preferential use of the left hand for food reaching.

Laterality was assessed in 100 human (Homo sapiens) subjects through the use of five measures of motoric behavior in three categories: locomotor, manual, postural. Locomotor measures included leading limb for initiation of walking and whole-body turning. Performance and questionnaire measures were used to assess lateral hand bias. Postural bias was assessed as the weight distribution in quiet standing. Population-level biases on the manual and leading limb measures were to the right; on posture and turning, to the left. Locomotor measures were found to be altered by marching experience. Only the manual measures were correlated. We compare the results with those of nonhuman primate studies that have used similar measures and discuss some patterns of laterality common to human and nonhuman primates.