But we do really...Personality is often lost when parts of the brain is damaged. Take pre frontal cortex lobotomy for example, the body lives on because the parts of the brain that support life sustaining functions are undamaged. The personality or "soul" is gone. How does the personality survive this to go on?
The brain has evolved many components over time that work in unison to give the illusion of self, damage to a critical component means loss of self, there is no soul.