Lately I’ve been playing around on Ancestry.com and thinking a lot about genealogy.

I find it very interesting to think both about how quickly the amount of ancestors you have increases as you move back in time and similarly how quickly the amount of descendants you are likely to have (assuming of course that you have kids who also have kids and so on.)

The exponential growth of how many direct ancestors you have is a pretty mind blowing thing once you really start trying to wrap your head around it.

For example if you go back 30 generations you will find that you should have over one billion direct ancestors.

Of course you wouldn’t actually have that many because a lot of those billion ancestors would be the same person. What? Yes!

Assuming an average of 30 years for each generation that would take us back about 900 years to the year 1111 AD.

There likely wasn’t even close to one billion people around in the entire world back in 1111. Maybe about 300 million.

Now consider that if you’re a white dude (or lady) like myself your ancestors over the last 900 years likely come almost entirely from Europe (I haven’t found any exceptions to this rule yet on Ancestry.com)

If there were 300 million people in the entire world 900 years ago, then how many were in just Europe? Maybe 100 million at most?

Now think again about that one billion ancestors number.

How many of those approximately 100 million Europeans were among my one billion ancestors? It seems likely that almost every single European alive in the year 1111 who had descendants is one of my direct ancestors.

It’s amazing to me to think about quickly we’re all related to one another, really.

And of course this is also true if we think about the future. If I were to have two children who then themselves were to have two children (and so on and so forth) then I would have over a billion descendants (again, many of them would actually be the same person! huh? yes!) before the year 3000!

It’s amazing to think about how every person who has descendants is effecting the make-up of humanity’s future. All billion of my ancestors (over just the last 30 generations) had to come together exactly as they did in order for me to be here today. That goes for you too. And of course it’s very likely that you share a common ancestor (and probably many of them) with me over the last 30 generations.

And how about that guy with the Reality TV show about having 19 kids? His DNA is going to be dominating like Ghenghis Khan.

If you want to check my math, pick up a calculator and start multiplying by two. You’ve got two parents, four grandparents, eight great-great grandparents, and sixteen great-great-great grandparents. 16 becomes 32. 32 becomes 64. You’ve got 128 great-great-great-great-great-great grandparents.

As you make your way back through your direct ancestors the number continues to double. And by the time you reach 30 generations you’re at 1,073,741,824.