This thesis analyzes the top two leading approaches in determining our personal identity in philosophy. It breaks down the history of the psychological approach and how that approach has addressed the problems argued against it. It also breaks down animalism which is a facet of the biological approach. The history of brainism is explained and the problems against it are analyzed. Finally, I introduce my theory of brainism that states that what we are over time is fundamentally brains. I believe that our personhood is housed in the cerebrum of the brain, and I argue for this point using evolutionary biology as the foundation. By determining the evolution of our brains in survival it is argued that the cerebrum has been an important portion of the brain that has allowed for safety through its ability to critically think, reason, and bond with others.