Against the Existence of Immortal Souls

From Sam Kean's very good 'The Disappearing Spoon',

• English philosopher Bertrand Russel...once used...medicinal facts about iodine to build a case against the existence of immortal souls.  "The energy used in thinking seems to have a chemical origin...", he wrote.  "For instance, a deficiency in iodine will turn a clever man into an idiot.  Mental phenomena seem to be bound up with material structure."  In other words, iodine made Russell realise that reason and emotions and memories depend on material conditions in the brain.  He saw no way to separate the "soul" from the body, and concluded that the rich mental life of human beings, the source of all their glory and much of their woe, is chemistry through and through.