Determined: A Science of Life without Free Will

by Robert M. Sapolsky

Then there’s a fun study where subjects were either made uncomfortable (by placing their hand in ice water) or disgusted (by placing their thinly gloved hand in imitation vomit).[*] Subjects then recommended punishment for norm violations that were purity related (e.g., “John rubbed someone’s toothbrush on the floor of a public restroom” or the supremely distinctive “John pushed someone into a dumpster which was swarming with cockroaches”) or violations unrelated to purity (e.g., “John scratched someone’s car with a key”). Being disgusted by fake puke, but not being icily uncomfortable, made subjects more selectively punitive about purity violations.[3] How can a disgusting smell or tactile sensation change unrelated moral assessments? The phenomenon involves a brain region called the insula (aka the insular cortex). In mammals, it is activated by the smell or taste of rancid food, automatically triggering spitting out the food and the species’s version of barfing. Thus, the insula mediates olfactory and gustatory disgust and protects from food poisoning, an evolutionarily useful thing. But the versatile human insula also responds to stimuli we deem morally disgusting. The insula’s “this food’s gone bad” function in mammals is probably a hundred million years old. Then, a few tens of thousands of years ago, humans invented constructs like morality and disgust at moral norm violations. That’s way too little time to have evolved a new brain region to “do” moral disgust.