US National Institutes of Health Director Francis Collins popped in for a chat with Stephen Colbert last night. Collins appeared on Comedy Central's The Colbert Report to discuss the new documentary he's involved in — HBO's The Weight of the Nation — on obesity in America. "Why are we under all this pressure from our biology? Because, we are creatures with genes designed to help us survive through much of our history where calories were pretty hard to come by," Collins said. "And if you couldn't find them, and absorb them, and hang on to them, you were done — the next famine was going to put you under. So we've been turned into these wonderful machines for finding calories and using them to put weight on."