Take a person that was born a year ago and call it John Doe.
John is now 1 year old.
Let’s take 25 years as an average number for a generation.
25 years ago John Doe didn’t exist, but his parents did. So, 25 years ago there were 2 of his direct ancestors living on Earth, and those were his parents.
50 years ago they weren’t there, but their own parents were. So, 50 years ago 4 of John Doe’s direct ancestors were alive – which was his grandparents.
75 years ago none of those people was alive, but their 8 parents were. So, 75 years ago, 8 of John Doe’s direct ancestors lived on Earth.
100 years ago their 16 parents were alive.

The multiplication factor is 16 per 100 years. In order to calculate how many direct ancestors of John Doe were living 200 years ago, you’ll have to calculate 16×16, which will give you the number of 256. If John Doe could travel back in time, and if he had the time and the technical means to visit all of them, he would be able to see and maybe talk to 256 of his direct ancestors who were living around the year 1823.

If you want to calculate the number of John Doe’s direct ancestors that were alive 400 years ago, you’ll have to multiply 256×256, and then you’ll get the number of 65,536.

So far, so good.

And now you’re eager to see how many direct ancestors of John Doe’s were alive 1,000 years ago – which is just the half of the period mentioned in my question.

In order to calculate their number, you’ll have to do this calculation:

65,536×65,536×256

The number that you’ll get is almost 1.1 Billion.

So, 1,000 years ago, 1.1 Billion direct ancestors of John Doe’s lived on Earth. Since we’re all interconnected, it means that they were not just John Doe’s, but our own direct ancestors.

But they all had 2 parents each, right? They had to have them, because if even a single one of them didn’t have even one parent, the whole calculation would crumble down and John Doe would have never been born. That’s easy to understand, right?

Now, in order to shorten the calculation and reach the year 1 AD, what do we do?

We simply do this:

1.1×1.1 = 1.21 Quintillion people.

1 Quintillion has 18 Zeros, which makes it equal to 1 Million Million Million.

So, it turns out that 2,000 years ago, the number of John Doe’s direct ancestors was 1.21 Million Million Million people.

If you compare that number to the actual population of 8 Billion, it will make roughly 150 Million Earths.

Question is, if there are as much as 150 Million populated worlds in the whole Universe.

So, back to my initial question, which was:

How many people lived on Earth 2,000 years ago? How can you explain their enormous number?

Topics: history, mathematics, world population