system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is jealousy, biologically?

Lately I've been suspicious of my boyfriend cheating on me.
I have no appetite, weak legs, can't focus, and a general "not good" feel.

What happens to your body when you're jealous? I'm intrigued!
gpt
Jealousy is a mate-guarding behaviour.
Our ancestors who got jealous more often took action to eliminate the threat/distraction.
The action might involve a huge piece of rock to the head.
Our inheritance of this trait speaks for its success.