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Every Person Is Our Cousin: We Are All Related

That all humanity is related is a well-established scientific fact. The DNA of all human beings living today is 99.9% alike, with our roots extending back to the earliest human species in Africa. But the oneness of humankind is also a mathematical reality. Let's take a look at how that works.

Every Baby Is A Royal Baby - In this video, mathematician James Grime explains why all of us are relatives of queens, kings, and everyone else on the planet! Note: I was put-off a bit by the opening enthusiasm for royalty, but the explanation of how ancestry relates all of us is worth it.
Humans Are All More Closely Related Than We Commonly Think - This Scientific American article explains in everyday language why it is that everyone on earth today is descended from a person likely alive somewhere in the world as recently as 1330 BC.
The explanations above are more detailed and complex than children may easily understand. Yet, the topic is so important and fascinating, I wanted to make it accessible to everyone, including children (at least eight-year-olds and up). So, I wrote the short story below for that purpose. You can also find the story in eReader formats with additional background information here.

We Are All Related

By Rick Johnson


Do you know that your family is very, very large?

That you have cousins, and cousins, and cousins all over the world in…




North America,

South America,

and Oceania?

Every person you ever meet…

Every chief or queen or king or president…

Every scientist and artist…

Every heroine or hero…

Every villager and farmer…

Every shopkeeper and immigrant…

Every person in trouble or need…

is a cousin of yours.

The only question is how far you must go in your family tree to meet them!

Does this sound like a crazy idea?

It’s not!

In fact, you can see why it is true with a simple experiment you can do yourself!

All you will need is:

  1. Some grains of rice or wheat or lentils (we’ll use rice, but any are fine)

  2. A chessboard or checkerboard. If you don’t have one, you can draw one on paper. Chessboards have 64 squares and most have squares that are two inches by two inches.

Then, put one grain of rice on one of the corner squares of a chessboard…

Then two grains on the next square…

and four grains on the next square…

and eight grains on the next square…

and so on.

What happened?

Did you manage to get all the grains of rice in all the squares?

Are you surprised how quickly you ran out of room?

The number of grains of rice you’d need for the last square on the chessboard would be more than 18 quintillion grains!

The actual number is 18,446,744,073,709,551,615!

That is more rice than humanity has ever produced. That amount of rice equals more than many thousands of years of the current annual global rice production!

What does this experiment have to do with your cousins?

It goes this way…

you have two parents…

four grandparents…

eight great-grandparents…

and so on, just like the grains of rice on the chessboard!

Let each square on the chessboard represent one generation of a person’s family tree, and it’s simple math to see that everyone on Earth is your cousin.

Go back only about 500 years and you’ve already got a million ancestors in your family tree.

Go another 200 years and you’ve got a billion.

Go on like this for about 40 generations, you already have more than a trillion cousins!

Whoa! Wait! If everybody has a trillion ancestors after 40 generations, wouldn’t that mean there were trillions upon trillions of people back then? How is that possible?

You’re right. It’s impossible for everyone to have a different trillion ancestors 40 generations ago.

40 generations ago—about 1,200 years—there were only about 200 million people living on Earth!

That means that your ancestors who lived 1,200 years ago show up not just in your own family tree, but thousands of times in other people’s family trees also! 

Do any of the following situations make us more, or less, likely to be related?

  • People who never have children?

  • Groups who have larger-than-average numbers of children?

  • Peoples who have stayed in the same place for generations, or even centuries?

None of these factors changes the basic reality that we are all related, as described above. The only effect these factors have is to determine how far back in history your family tree has to go before it meets a common ancestor with everyone else, and where on the planet that meeting happens.

It is certain that there will be ancestors who appear at least once in every person’s family tree.

As you go further and further back through the generations, we reach an inescapable conclusion: there was a time when the people alive on Earth were ancestors to all of us living today!

Except, of course, those who did not have children.

Every person you ever meet…

Every chief or queen or king or president…

Every scientist and artist…

Every heroine or hero…

Every villager and farmer…

Every shopkeeper and immigrant…

Every person in need…

is a cousin of yours.

We are all related.

Sissa/Sessa And the Origins of Chess - Did you know that the origin of the game of chess is related to the topic in today's post? Read about the legend of Sissa (some call him Sessa) and the legend of his creation of the game, which illustrates the 'wheat and chessboard' concept mentioned in the story above.

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