His demands, which are posted here, include the demand that Discovery Channel start airing shows that offer solutions to the planet's problems, and that "All programs promoting War and the technology behind those must cease."
The document also demands that Discovery stop promoting childbirth in its shows, and that it must "Develop shows that mention the Malthusian sciences about how food production leads to the overpopulation of the Human race. Talk about Evolution. Talk about Malthus and Darwin until it sinks into the stupid people's brains until they get it!!" The gunman also demands shows that offer solutions to problems with immigration, pollution, and the US economy.
So far, it appears that nobody has been hurt.
UPDATE: Police say the gunman is James Jay Lee, who has protested before at the Discovery Channel building. It appears that he has one hostage, still unhurt.
UPDATE: Police have shot the gunman, and his three hostages are now safe.
Image most likely of a first responder heading toward the Discovery building, but has not been verified by police. A source who works inside the building says it is unlikely this is a picture of the gunman.