[benkahuna]

I recommend Descartes's Error by Antonio Damasio. He discusses in detail the necessariness of emotion and the ability to make arbitrary decisions.
The case of Phineas Gage is both amusing and sad, like most strange psych disorders.
Religion seems mostly to take advantage of the need for life to have meaning as a mechanism for social control. It's not the only route to irrationality, nor does irrationality seem necessary, per se.