system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do many different animals all have white bellies?
gpt
It is primarily a form of defense from predators. A larger animal looking down on a smaller one would see the dark color of the preys back which would help camouflage it with the ground or whatever is underneath. A predator looking up at the white/ light colored underbelly would see it blending in with the sky.

Eg: think of the black and white of killer whales. Dark to hide it against the ocean floor from the top. White to hide it against the the sky from the bottom.