That's just... false. Disgust is a response we evolved to keep us from eating things that could kill us.

It's probably a mixture, but who knows. Chomsky and Skinner could probably debate it for several lifetimes.

It's actually both! Freakonomics did a great segment on the difference and the different types of disgust. https://freakonomics.com/podcast/disgust/

Fair enough. The point about aging that I had in mind doesn't change if we redefine 'natural disgust' as 'culturally taught disgust' In general, the older you get, the further you get from mum and dad dictating your behavior, and so the less enjoyable it is to, for example, be rude/crude for its own sake.