On the Heresy Corner blog, The Heresiarch has been writing about the recent news of twins who were adopted separately at birth and got married without knowing they were siblings. He makes a good cases that it's BS.
He also links to Jon Henley's column in The Guardian:
Assuming your brain is still functioning like the well-oiled piece of precision engineering it is, your response would, I trust, be: "That's a wind-up if ever I heard one. Think about it for a minute – you mean these two meet by accident, discover not only that they were both adopted but were born on exactly the same day in exactly the same town, and still never pause to wonder whether they might be related? Pull the other one. What did it say on their birth certificates?"