Posture and reaching in chimpanzees (Pan troglodytes) and orangutans (Pongo pygmaeus).

Hand preference in reaching was assessed under 2 postural adjustment conditions in 40 chimpanzees (Pan troglodytes) and 9 orangutans (Pongo pygmaeus). The postural conditions were quadrupedal and upright, during which reaching for food was scored on a minimum of 50 trials. Results indicated no population preference during quadrupedal reaching but a right-hand population preference was found during upright reaching. There were no significant effects of age or sex on either the direction or strength of hand preference. Early rearing history affected the strength of hand preference but not direction. The results suggest that posture is an important factor in the assessment of hand preference in great apes and may have important evolutionary consequences.