When you scale animals you can’t just keep everything in proportion. For example, volume grows as the cube of linear dimension, but surface area only as the square. So as animals get bigger they have trouble radiating heat. That’s why mice and rabbits are furry and elephants and hippos aren’t. You can’t make a mouse by scaling down an elephant.
— Paul Graham (via christmasgorilla, my favorite Tumblr username, because his name is Chris Muscarella — say it out loud — get it?)