Dexterity of the human hand, an important characteristic of humanity, is often attributed to advanced neural circuits in the cerebral cortex. However, recent studies led by a research team from Tamagawa University and the National Center of Neurology and Psychiatry have unveiled that both ancient spinal cord circuits and newly evolved brain circuits work together to provide flexible and stable hand movements. This collaboration allows humans to perform intricate tasks like writing, using chopsticks, and playing musical instruments.

Through experiments with Japanese macaques, the researchers compared the dexterity of various primate species and discovered that while other mammals like rats have independent fingers, they lack the ability to grasp effectively. In contrast, primates such as the squirrel monkey can grasp, but their thumbs do not face the other fingers, limiting dexterity. The evolutionary adaptations seen in macaques and humans enhance this functionality, as humans exhibit opposable thumbs that enhance fine motor skills.

The findings suggest that two main neural pathways— one from the cerebral cortex and another from the spinal cord—significantly contribute to hand movements. The research, published in the journal Science Advances, emphasizes the importance of both ancient and modern neural networks in allowing for the sophisticated dexterity known in humans, setting them apart from other animals in terms of manipulative ability.