Look-alikes

What with the hoopla over public transportation in NYC re: bag searches, I thought I'd pose a more timeless public-transportation-related question: Has anyone else ever seen this happen? You're sitting on the bus or the subway, and you see two people nearby, sitting next to each other, who look like parent and child, siblings, or possibly even identical twins. But then you notice that they're saying nothing to each other, you remember that they didn't even get on the bus/train together, and then one gets off the bus/train without saying anything to, or looking at, the other. The two people are not, at least to their knowledge, in any way related to each other. And yet they look so much alike that there's no way they could not have very close biological ties to each other. Am I the only one who's ever witnessed this phenomenon? It's super creepy.