The species is raccoon and the environment is in the forest. The predator is a tiger and the food is grass.
In a new environment
The 2 versions of the raccoons are different by the fur color and skin color.
One day a big tragic event happened where it just started raining really hard and there was a huge earthquake that happened for 3 days straight and all of the trees started to fall down on the raccoons.
The new environment is more successful for the raccoon that has gray fur because they can camouflage with their new environment.
The successful variation was the raccoons with the gray fur and the unsuccessful variation was the raccoon with the black fur.
The raccoons with the gray fur has evolved in the gray cave they are a new species and they won't reproduce with the outside raccoons.