You have two parents four grandparents eight great grandparents and so forth a If all your ancestors were distinct what would be the total number of your ancestors for the past 39 generations counting your parents generation as number one Hint Use the formula for the sum of a geometric sequence b Assuming that each generation represents 25 years how long in years is 39 generations yT e The total number of people who have ever lived is approximately 100 billion which equals 1011 people Compare this fact with the answer to part a What can you deduce Select all that apply some of my ancestors must not have had children There could not have been 39 generations in my line of ancestry People have been living on earth for less than 1 100 years Some ancestors on different branches of the family tree must be the same