system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we feel jealousy?
gpt
It's all wired in us. We feel jealous to encourage us to be better than that person.

Let's go back in time about half a million years ago...

Oog and Gork are neighbours. They are hunting buddies and they have known each other for years. The two go on a hunting trip. Oog is bigger and stronger and can throw the spear further and faster than Gork. Gork took down a 300lb deer while Oog took down a 600lb deer. 

Gork will obviously be jealous.

Suddenly, a group of females nearby notice Oog carrying the freshly killed deer on his back and start flocking towards him. They then go back to Oogs's cave and start mating.

Now Gork will be very jealous.

Simple enough?