Most people think of a Family Tree like a triangle. It starts with you and then branches out downward from there, starting with your children and then your grandchildren, and so on. The lesser looked at side is the other direction. Starting from you and moving up. This makes an upside down triangle. There’s you, then your two parents above you, then each of their two parents above them, and so forth. As you keep moving up a generation the number of ancestors, or the number of people it took to create you, doubles. If you know anything about exponential growth, you will realize this number can get very large very quickly.
If you were to go back seven generations (your great-great-great-great-great grandparents) you would have 128 ancestors. This generation would have been in their 20’s in approximately 1800-1825, which means if you traveled to the year 1820 there would be 128 people walking around all making up an equal 1/128th of who you will become in 200 years.
Now let’s go back 12 generations. You would have to say “great” 10 times before saying “grandparents”. These people would be in their 20’s, in about the second half of the 1600’s, and again if you traveled to that time, there would be 4,096 people that make up who you are.
Now if you continue to double your ancestors, eventually you will surpass the world population, which obviously isn’t possible. This is why there is a widest part of your family tree. This part of your family tree happens in about the year 1200, where you are related to almost the entire world population. This means that everyone alive today has many common ancestors from that time.
If you continue to go backwards your family tree begins to get smaller. The reason for this is because hundreds of years ago people didn’t tend to meet as many people in their lives. Transportation wasn’t what it is today and big cities weren’t a thing, so the people in the small village you lived in tended to be your only contact. This would mean that someone could have two ancestors that were very closely related to them. For instance, if two cousins got married (which was far more common back then because of the proximity issue) than their child would only have 6 great-grandparents, instead of 8.
So if you think about it, if you are a descendant from that many people, odds are somewhere up your family tree is a king or queen or someone really cool and important. If anyone tries to brag to you that they are somehow related to King Henry VIII or something, you can just tell them that you probably are too. He just might be your 19th cousin or something ridiculous like that.