Why do mice have fur, even in warm climates?

I need an explanation on why mice have fur, even though they might live in a high temperature climate, such as the rainforest.Why do mice have fur, even in warm climates?
Warm climate or not... it can get very cold when the sun goes down.Why do mice have fur, even in warm climates?
Small mammals lose proportionately more body heat than large ones. This makes temperature loss a relevant problem for small critters in even tropical places. Fur also provides other functions such as keeping the moisture out and protection of the skin against abrasions.
They have fur because they feel like it and that's that. Also that's the way God made it and he likes it.

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