A small display at the fish hatchery where I work describes a now-extinct fish called the Michigan Grayling. Last summer, I had the following conversation with a tourist...  

"Is the Grayling still extinct?"  

"Yes, sir," I replied, "it no longer exists."  

"Any thought of bringing it back?"  

I don't think that's possible."  

"Why not?"  

"Because it's extinct."