How You're related to everybody else!

For a moment, consider every person you have ever met, every person you have ever heard of, and lastly, consider every living person on the planet right now, regardless of how close or how far away any of these people may seem to you. Since we are all related to each other and you are all related to me, how is it possible that we can look at your family tree using some very basic math?

Going back just five generations ago, or 125 years before the date of your birth, you would have theoretically had 32 ancestors living on Earth at that time; however, going back a thousand years before you were born, or forty generations ago, you would find with this math that you would have over a trillion ancestors living in the Middle Ages. This is more people than have ever existed in all of time combined. You obviously had two parents, and your parents each had two parents of their own, meaning you have four grandparents and eight great-grandparents, and this number doubles with each generation.

The only people someone may ever really meet are those in their local village, town, or tribe. This obviously limited the dating pool to just a handful of options, and those options frequently included people like cousins. Not all of your ancestors are unique to you or your family. If you compare your family tree with your friends tree and go back far enough, you'll see the shape of the tree slowly vanish and see something that resembles more of a web as you draw your two webs out. Clearly, there's a variable we haven't taken into account in these calculations yet, and that variable is incest.

The further back in time we go, the more common ancestors we end up having. Approximately 0.5% of the modern human population can claim direct ancestry from Genghis Khan, largely in the region of Asia between China and Uzbekistan. Going even further, nearly anybody with European ancestry can trace their origins to the same group of ancestors approximately 1,000 years ago. You will eventually find a common ancestor between yourselves at some point, making you both distantly related.

Since Charlemagne had eighteen children, he is probably somewhere in your family tree. However, the most recent person to whom all of us living on Earth and watching this video can mutually trace all of our ancestors back is known as the most recent common ancestor, or MRCA, and it is thought that they may have existed as recently as 300 BCE. This means that statistically, if you have European ancestry, anyone living in Europe around the ninth century who had children and grandchildren is one of your direct ancestors.

This person had amazing reproductive success and was probably a merchant who traveled extensively with their offspring, venturing off and creating their own offspring over time in far-flung parts of the world like the Americas and Australia. This one human who lived there at this time is the direct ancestor of every single person alive today, which links all of us together in the enormous family web that we call humanity. This person lived somewhere in East Asia, probably in either Chaka Japan, Taiwan, or Indonesia, shortly after Alexander the Great's conquests.

MRCA is merely the first person in world history who can count universal descendants today, but many of our ancestors lived much further in the past than they do. This does not mean that MRCA was the first person to have children or that no one else alive then has direct descendants today. A 9,000-year-old skeleton known as "Cheddar Man" was found in a cave close to the English city of Cheddar in 1903. A recent DNA analysis of the remains revealed something astounding: 300 generations and 9,000 years ago, there was a direct descendant of Cheddar Man who lives today and teaches history. He lives only 0.5 miles from the cave's edge.

If you go even further back in time, it's possible that 70,000 years ago, there may have been as few as 10,000 people on the planet. That's less than 9% of the seats in Wembley Stadium. And when you consider that those few people were dispersed throughout Africa and Eurasia, you recall that most people only ever dated people who lived nearby because they had no other options. If you think about it in words like this, we all have many common ancestors from whom we can all claim to be related; the most recent one is the guy who lived in 300 BC. You are the first individual in an uninterrupted line dating back hundreds of thousands of years to fail at having offspring.

In fact, it gets even worse than that when you think about the last Universal Common Ancestor, or Luca for short. This organism is thought to have existed between 3.5 and 3.8 billion years ago, and everything that is alive today—from you and me to bananas that annoy mosquito Greg and the bacteria on your face—is a direct descendent of it. If you think about it that way, you're the first organism in an unbroken chain that dates back more than three billion years to fail, and that could make your ancient ancestor, Luca, very sad.

The intriguing thing about all of this, though, is that if you go back far enough, not only is humanity itself one enormous interconnected family, but all life on Earth is just one enormous, incomprehensible, interconnected family. So, the next time you step on a bug or SWAT a mosquito, keep in mind that you are both technically a part of the same large family. The origins of both humanity and life itself are as intriguing and mysterious as they are mysterious, but there is still a surprising amount of information that we can determine using math, such as where your ancestors most likely originated.

Because we are all directly descended from these scientists, who work like detectives investigating centuries-old crime scenes that have an actual impact on us today, the computational biology course at Brilliant will explain to you how all of this works and why it matters to you personally. In fact, the course includes a whole section on human ancestry.