As for being descended from the same person, the evidence for this is because every blue eyed person alive today has this same mutation.
Scientists reckon only 8 to 10 per cent of the population have blue eyes and eyes don't fully develop in childhood meaning the brown pigment can kick in later, causing blue eyed children to end up with brown eyes in adulthood.
So if you have blue eyes, now you know - your family is a lot bigger than you might have thought previously.
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