lateralization (lateralized): divided into a left side and a right side, with control of functions on one side or the other (used in describing the human brain)
About two million years ago, there is evidence that humans had developed preferential right-handedness and had become capable of making stone tools. Tool making, or the outcome of manipulating objects and changing them using both hands, is evidence of a brain at work.
The human brain is not only large relative to human body size, it is also lateralized, that is, it has specialized functions in each of the two hemispheres.
Those functions that control the motor movements involved in complex vocalization (speaking) and object manipulation (making or using tools) are very close to each other in the left hemisphere of the brain.