ABSTRACT

In any consideration of comparative neural mechanisms of behaviour the general characteristics of the brain reveal a common pattern throughout the vertebrate series. It is important when considering the evolutionary changes involved in encephalization, that one does not create the impression that they are solely restricted to the brain. Major changes also occur in the organization of the spinal cord. Higher vertibrates show less normal autonomy of the cord and have a greater dependency on the brain in the control of spinal reflexes in locomotion. Considering the brain weights of outstanding individuals in isolation is a highly arbitrary and not a meaningful practice. Change in the size of the brain with evolution is only one aspect of the situation. There are also other factors such as changes in cerebral organization with increasing size, changes in the types of cell with encephalization, and changes in the complexity of neural networks.