Sometimes a person's corpus callosum is split, which separates the two hemispheres completely. this is done to a. study the effects of a split brain. b. change a person's personality. c. determine the precise area of cognitive functioning. d. control epilepsy.

The corpus callosom is a bundle/band of nerve fibers found deep inside the brain. This connects the right and left hemisphere. Corpus Callosotomy or otherwise known as "Split-Brain" surgery is a procedure where the corpus callosum is cut. This is done to control epilepsy but only as a last resort.

The surgeon can partially or completely cut the corpus callosom. If  a partial dissection is enough to control seizures, they would stop there. However, if the seizures goes uncontrolled, it is completely dissected.  

It might. it might because if you think about if they discovered if we came from (lets say something funny like aliens) and thy found cells that matched and they would have t do more research about it but would most probably change their theory.