 In my prior video, I pointed out that everyone alive today has descended from Julius Caesar, Cleopatra, and Confucius. A lot of people thought I meant related, as in a cousin of a cousin of a cousin kind of relation, but I chose my terms carefully, if not my historical figures. Let me say it again. To the best of our knowledge, everyone alive today is not just related, but actually descended from every historical figure who lived before a few thousand years ago. Caesar was a poor choice, not because he left no heirs, but that we don't know exactly who they were. His campaigns in Spain and Germany probably included leaving behind several illegitimate children, some of whom would have left heirs in all likelihood. However, let's choose an easier target for our big trip through our shared genealogy. Confucius was an actual historical figure who lived in China in about 500 BC, and he is your direct ancestor, whomever you may be. It so happens that his genealogy is one of the most extensively documented, at least along the paternal line, and he is the documented direct ancestor of millions, with billions more that can't trace their ancestry, but are nevertheless direct descendants of Master Kong. This population, in fact, most probably includes all living humans, whether they be European or African or South American. Let's review the evidence. Point one, you have millions of ancestors. I went over this briefly in my prior video, but in every generation, you hypothetically have twice as many direct ancestors as in the prior generation. In fact, this breaks down rather quickly as most of your ancestors were related to each other, if we go far enough back, called pedigree collapse. I'll come back to that fact in a minute. I'm going to use a lot of rounding here, because I'm a biologist, not a mathematician. Assume 20 years per generation, and the hypothetical doubling of ancestors in each generation. Everyone has a mommy and daddy. Given 10 generations, or 200 years, you had 1000 ancestors. In 20 generations, or 400 years, about the point where European colonies were established in the New World, you had about a million ancestors. A mere 500 years ago, about the time of European contact with indigenous Americans, you had 33 million ancestors, about 10% of the world population at the time. By the time we get to the period of Confucius, the number of ancestors is a number with 37 zeros behind it. Clearly more than a number of people who have ever lived. All of these numbers are based on the hypothetical doubling. In fact, the further down the line we go, the more we are counting the same person twice in your ancestry. Nevertheless, the evidence is that your ancestors include nearly everyone alive at any point prior to about a thousand years ago. In fact, our best models have 80% of everyone prior to about 500 BC, either being the ancestor of everyone alive, or of no one alive, their line either when extinct or spread to every corner of the globe. Which leads me to point two. There are two metrics, the universal ancestor point and the identical ancestor point. I've come up with a very crude way to illustrate these concepts. We'll start with a simple blue pyramid representing your ancestry. It expands as we go back through time. Let's take an Inuit from Canada, I call him Anook, and give him an ancestry pyramid as well, this time in pink. You'll notice that his ancestry pyramid will eventually overlap yours. In the case of Anook, it may not be until fairly recently, say about 300 years ago, following European expansion into the New World. In a relatively few generations though, even a single couple can end up being the ancestor of virtually everyone in the Americas. An ancestor you most recently share in common with Anook is called, well, your most recent common ancestor or MRCA. Now if we took everyone alive today and overlaid their pyramids, we would converge on a single ancestor that we all have in common. This would be the universal most recent common ancestor. The best estimates of simulations using realistic data put the date for this convergence somewhere between 1400 BC and 50 AD, so somewhere between the height of the Egyptian Empire and the time of Julius Caesar. Another metric we can look at is the identical ancestor's point. If we zoom out a bit from your and Anook's ancestry pyramid, we see that pedigree collapse, the marriage of cousins, is shrinking the slope of our pyramids. Eventually that collapse will require that all of Anook's direct ancestors are all of your direct ancestors. And this point occurs not nearly as far back as you would think. Somewhere between 2000 and 5000 BC, everyone alive at the time was either the direct ancestor of everyone alive today or the ancestor of no one alive today. About 80% of everyone who lived during the time that saw the founding of Athens, the beginnings of Judaism, and the fall of Troy is your direct ancestor, and also Anook's. The other 20% of their contemporaries around the globe had a line that died out completely. An interesting side note, this process works in the other direction as well. In a few hundred generations, you will either be the ancestor of everyone alive, or your line will have perished from the earth. How's that for immortality? This discussion will be continued in Part 2.