For twins, Lucy and Maria Aylmer from Gloucester, England who have been made to produce their birth certificates to prove they are related, they aren’t alone. In the US, the self-identified “multiracial” community is at 9 million and climbing. So why is it so difficult for so many to believe that the two girls are related even after being told of their biological ties? Well, our notion of “race” and the historical “one-drop-rule” may be a good place to start…