A small-town guy gets a job in New York. He finds an apartment in Queens, figuring he'll take the subway to work every day.
On the first day, he notices that one of his fellow passengers is rather hairy with a heavy brow. He's wearing a loincloth of animal skin and carrying a stone spear. In short, a Neanderthal. Nobody else seems to be paying attention (you know how the subway is), but the guy can't believe his eyes. Eventually, he plucks up courage to ask.
"Excuse me, sir. I hope you don't mind my asking, but... Are you a Neanderthal?"
"Yes. Yes, I am," answers the Neanderthal. "Why do you ask?"
"Oh, no reason, no reason," answers the guy. "It's just... Well, I thought you guys went extinct."
"Well New York is a blue state," answers the Neanderthal. "But there are still a few of us around."
"Right, right," says the guy, and a short silence falls.
"New to the city, are you?" asks the Neanderthal, politely.
"Oh yeah," answers the guy. "I just moved here at the weekend. I'm from Montana originally, a town called Hamilton."
The Neanderthal's face suddenly goes blank and he takes a step back. At that moment, the train pulls into a station and the Neanderthal backs off the train and disappears into the crowd. Everybody left in the subway car is staring at the guy in an unfriendly way. Not really sure what he's done, he thinks he'd better find out. One lady looks less unsympathetic than the others, so he decides to ask her.
"I'm sorry, I'm new here. Can you tell me what I said wrong?"
"You really must be new," answers the lady. "Everyone around here knows: you never evolve if you commute with a Hamiltonian."