It may seem like a form of positive reinforcement, but that’s what it is: When a network like National Geographic presents something that used to be at the very core of what it once presented, I’ll most likely support it.  Tonight, for example, is a three-hour special about Charles Darwin and his voyage to and extrapolations from the remote island of Galapagos. Even given the recreations with a Darwin “actor,” this special is precisely what National Geographic Channel is all about. Or should be. Unfortunately, in some respects, the network has… devolved.