The extent to which observed behavior in the complete commissurotomy patients is supported by only one hemisphere would depend on individual differences interacting with a variety of factors such as genetics, intelligence, and so on. The lesson imparted here is that there is sufficient functional redundancy in the neocortex so that the capacity to maintain a wide range of abilities is within the control of one hemisphere. And, yet, as seen in what is missing in the patients' behavior, one hemisphere (...) is not quite enough. Nature seems to have intended that the two hemispheres complement each other, that the full range of human behavior be best accomplished through interaction between the left and right hemispheres. (shrink)