Dear Dr. Boli: I have to do a research project on ancient Egypt for Mrs. Hurdle’s tenth-grade social-studies class, and there’s one question I can’t find the answer to. What was the total population of the earth about five thousand years ago, when Egyptian civilization was ramping up? It wasn’t in my history book. —Sincerely, Maximilian F. O. P. Pond IV, Mrs. Hurdle’s Tenth-Grade Social-Studies Class, Point Breeze Preparatory Academy for the Idle Rich.
Dear Sir: Let us see if we can solve this problem mathematically. You have two parents, and your parents each had two parents, and so on back through the generations. Estimating about three generations per century, we have 150 generations back to the time five thousand years ago for which you are looking for a population estimate. Therefore, we simply calculate 2 to the 150th power, and we find that there were about 1,427,247,700,000,000,000,000,000,000,000,000,000,000,000,000 of your ancestors alive five thousand years ago. Now, at the present moment there are roughly seven billion people on earth, and each of them has a similar ancestral tree. Therefore, we need only multiply our result by 7,000,000,000, and we shall have a very good estimate of the population of the earth five thousand years ago.