Here’s an interesting example of how the press constantly give out half-truths and misleading information. This from a comment in the Indy.
It is interesting that Benedict Cumberbatch and Sir Arthur Conan Doyle share John O’Gaunt as a common ancestor, but perhaps not such a coincidence when the statistics are considered. Each of us has two parents, four grandparents, eight great grandparents and so on, doubling the number of our ancestors for each generation we go back. By the time we go back 20 generations (say about 600 years) we each have more than a million ancestors (1,048,576 to be precise). As the population of England is estimated to have been only about 2 million in the year 1400, any two people whose families have lived predominantly in England during that period have quite a high probability of sharing a common ancestor.
Dr John Coppendale Cambridge
So it rather seems that an awful lot of people are related to the two named above.