Population-level directional bias was not evident for any task for rhesus monkeys and was observed only in the bimanual task for chimpanzees.

The strength of the effects, however, depends on which hand is used in the unimanual task and the type of bimanual task performed.

The majority of rhesus monkeys and chimpanzees showed significant lateral biases when reaching from a freestanding posture and when engaged in a coordinated bimanual task.

We examined hand preference in 22 rhesus monkeys and 79 chimpanzees using unimanual reaching tasks varying in postural stability and in a coordinated bimanual task.