Structure of the Brain
As a large amount of interactions in everyday human life are repetitive (e.g. walking, sitting, etc.), but happen in dynamically changing environments and conditions, they are initially activated by the right hemisphere (as mentioned earlier) and then, based on the reasons mentioned earlier, switch between the hemispheres.
Structural symmetry of the brain is based on the dynamic intra-process hemispheric traversing nature of interaction processing
The optimizing aspect of the evolutionary process has also resulted into brain structured in such a way that locations where different functions are processed are closest in distance to each other based on their frequencies and usage patterns, which helps optimize its operations by increasing processing speed and saving energy.
Based on the switching of new and repetitive interactions between hemispheres mentioned earlier, as relations between function processing areas of such interactions are the same in both hemispheres; structures of most interaction processing areas in both hemispheres are similar.
Such optimization does not only work within function processing areas of interactions in each hemisphere, but between the hemispheres too (i.e. those that are frequent or time critical between the hemispheres are closer), resulting into interaction processing areas of brain being structurally symmetrical.