Neural and genetic basis of dexterous hand movements.

An ability to control dexterous hand movements is considered to parallel the evolutionary development of the corticospinal tract and the appearance of direct connections between corticospinal neurons and motoneurons (the corticomotoneuronal (CM) pathway), which developed uniquely in higher primates. However, recent studies have revealed that some non-primate animal species have higher levels of dexterity than previously supposed, and in higher primates, various indirect non-CM descending pathways have been shown to participate in the control of dexterous movements. More recently, the CM pathway was shown to exist in rodents during early development, suggesting that rodents and primates diverged in their reliance on the CM pathway at some point in evolution, thus challenging the traditional view of the sequential development of hand control from rodents to primates.