Most scientists believe individual nonhuman primates can exhibit hand preference in certain manual tasks, but that there is no population-based hand dominance in prosimians, monkeys or apes like there is in the human. This paper critiques the studies attempting to find hand dominance in nonhuman primates. It also critiques a recent study seeking evidence for brain asymmetry related to hand preference in squirrel monkeys. The investigators felt their data showed that the motor cortex hemisphere contralateral to the preferred hand of squirrel monkeys had a greater number of microstimulation sites that caused forelimb muscle contractions than did the ipsilateral hemisphere. Their conclusion may have been based on faulty reasoning. Any evidence that nonhuman primates have a system homologous to that of human hand dominance (or any correlated brain asymmetry) is very weak indeed. In fact, evidence from these studies of nonhuman primates would support separate ancestries of the different types of nonhuman primates and of humans; although the evidence has not been interpreted in that manner by those who have undertaken the studies.
