I know the first thing that would spring up to mind is depression but that seems to be a reduced sensation of pleasure from the people I’ve talked to with many emotions still present but almost “muddied”.
I mean a lack of pleasure in the sense that food, sex, warmth, or recreational drugs wouldn’t trigger any ‘noticeable difference’ or non at all. (oppositely like having a random itch that that goes away as opposed to a concrete throbbing sensation of pain).
Is there a reason why a genetic mutation couldn’t cause that? Is physical and emotional pleasure as necessary from an evolutionary perspective as negative emotions and pain?
There’s at least one gene that has been found to have some association with anhedonia.
Pain motivates behaviors that mitigate immediate risks to life - but pleasure (not just the absence of pain) motivates important behaviors, too. Emotional pleasure motivates socialization, which strengthens social bonds that may increase probability of survival of oneself and one’s offspring. Emotional pleasure associated with victory also motivates healthy males to win in pre-mating dominance contests, which increases probability of sexual access to the female of the species - and physical pleasure motivates mating, which enhances the probability of propagating one’s genes to the next generation.