In his travelogue, Following the Equator, Mark Twain has this funny passage about all the benefits nature provides to animals, in comparison to what it provides to humans. For those that fly, he writes, nature gives a home forty miles deep, spanning the globe, without any obstruction. For those that swim, nature provides a home that covers 4/5ths of the earth. But to man, he says, nature has gifted thin skin and miles upon miles of barren snow, …