How to account for all of your ancestors?

Question

The human population in 0BC is estimated to be around 188,239,090.

 

You have 2 parents, who each had 2 parents (2²) , who each had 2 parents (2³), etc. Assuming 5 generations per century (5x20) back to 0BC is 100 generations or 2¹⁰⁰ parents.

 

2¹⁰⁰parents is 1,267,650,600,228,229,401,496,703,205,376 ... how is that possible?!

Answer 1

5 generations per century is a bit much.

It might be about 30 to 35 now and maybe was 20 once upon a time.

From my parents to me was 22, from me to my kids was 33, from a cousin to his kids it was 45.

 

Also, because of the variations in ages when people had children and when they died you cannot really assume each generation back was alive at the same time.  For instance one of my parents has a whole set of cousins that are about my age due to someone a generation ago having children late and another having them early.

 

Another thing you have assumed (and shouldn't have) is that none of your great-grandparents had a common great-great grandparent. 

- The proscription against marrying 1st cousins is one of our culture and times.  It was not always true, and still today is not always true, some 1st cousins do marry, and is not necessarily even true at all in some  cultures.  It certainly was not always true in past times.

- In addition that proscription only goes as far as 1st cousins.  A good deal of 2nd cousins marry, many more 3rd cousins, etc. - especially over generations.  Also in the past communities were much smaller in general.  The intermarriage rate would have been greater in the past.  Especially in small villages.

 

The equation is much more complicated than you make it out to be.

Answer 2

     That's a crazy number isn't it! And good for you to question this number!!! Here's the catch. If all your ancestors were immortal, the earth would be a very crowded place. You may want to look up the average life span of those times. 35 was old. Some years the death rate was larger than the birth rate......war, disease, natural disasters...

     That is, however, how many ancestors you've had.....kind of amazing!!!