What evolutionary advantage affords most of the nerves on the left hemisphere of the body to be attached to the right hemisphere, and vice versa? For example, the right visual field is processed in the left hemisphere, and vice versa. Why should this be so? I can see no reason for this. Originally I considered that this would somehow allow for some redundancy in case of injury, since having to cross the network from one side to the other forces the nervous system to mesh, but I don't really know the reason.