system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] Why do we sometimes have to gag when we only see disgusting things?
gpt
Because you have an evolutionary incentive to do so.

Your ancient ancestors had an omnivorous diet of fruits, nuts and meat where they could find it. Imagine you see that the inside of a carcass you're eating is rotten and full of maggots. Gagging is your brain telling you to eject the contents of your stomach to avoid poisoning yourself.

This is also the reason why you feel the need to vommit when someone else does. You may have ingested the same poison. After all, if that ape is near you then they're probably in your group. And you're probably eating the same thing they are. Therefore better safe than sorry.

Sure...you may lose the contents of your stomach, but it's better than death.