1.  Number of Ancestors The number of direct ancestors a person has had is given by Great-great-grandparents Great-grandparents Grandparents Parents This formula is valid provided the person has no common ancestors. [A common ancestor is one to whom you are related in more than one way. For example, one of your great-grandmothers on your father's side might also be one of your great-grandmothers on your mother's side (see figure).] How many direct ancestors have you had who have lived since the year 1 A.D.? Assume that the average time between generations was 25 years (resulting in 80 generations) so that the total is given by Considering your total, is it reasonable to assume that you have had no common ancestors in the past 2000 years