Biome Shifting Animals?

Considering how Zombies and Skeletons can change their variant form under specific climates - either hot or cold - and given that pigs, cows, wolves, and chickens all gained biome variants recently, I've had a few thoughts.

• The animals should change form when prompted to do so by their environment.
• Wither skeletons likely followed a similar evolutionary path before dying.
• Mooshrooms, Cluckshrooms, and Hoglins all likely resulted from this form change.
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