We're going to talk about royalty! The royal family, are you a fan of the royal family? (Brady: Not particularly, despite the decor in the room.) [Laughs] Don't you love a royal baby? Wills and Kate mug? Megan and Harry commemorative plates?
- (Brady: I'm alright with royalty.) [Laughs] So a big thing was made when Prince Harry married Meghan Markle because he was marrying a non-royal. I said, I was like, "Oh, marrying a non-royal! How good!" And then they looked into Meghan's family tree. It turned out when they looked into it that she is distantly related to King Edward the Third! Which is kind of surprising. And then maybe even more surprising is Kate Middleton, who was also meant to be a non-royal is distantly related to King Edward the Third! Which means Meghan and Kate are distant cousins! Is that surprising? Well, it turns out lots of people are related to King Edward the Third. Ellen DeGeneres is related to Edward the Third. It turns out everyone is related to royalty at some point. Everyone is directly descended from royalty somewhere in their family, and that includes you as well. Well, we can do this quickly in fact. Everyone has two parents. And then they have two parents, so everyone has four grandparents. And everyone has eight great-grandparents. And then sixteen great-great-grandparents, and you keep doubling this up. If you went back 30 generations, I dunno, about a thousand years, you'd end up with over a billion ancestors, direct ancestors. But we all have a billion direct ancestors! So straight away, you can see that the family trees - we're not just, we don't just have separate family trees. If we look at our family trees, we are far more connected than you think. We are this connected web of families. In fact, you only have to go back a few generations. If you looked at your, I dunno, great-great-great-great, grandmother, you can actually find out that she might be your great-great-great-great grandmother in more than one way, which means you don't have sixty-four great-great-great-great grandparents. You have 63, or fewer! But that itself doesn't show that we're all descended from royalty. So we're going to do a little experiment to show you the kind of idea. (Brady: Because you could argue that royalty is like a special case.)
- They could be. (Brady: They're quarantined off.) Yeah, they could be their whole separate strand, couldn't they? Let's have a look at how we are all connected. What I'm going to do is do a little experiment and I'm gonna have a population of, let's do a simple thing, six people. Now we're gonna work out who their parents are going to be. We're going to go back a generation. So we might go back a generation like this. Three, four, five, six. In fact, I know I'm gonna do this a few times. Let me just prepare this. This population down here at the bottom of the page, this is going to be the present day. This is the present generation. Now, we're gonna work out who their parents are, and I'm gonna use dice for this. We're gonna start with individual 1 and their parents was one and five. Parent 1 and parent...5 up here. Let's do this for individual 2, let's work out who their parents are. Strangely, some kind of virgin birth here! But no matter, I'm going to persevere with this. So this has just had one parent, five and five, okay, let's see what individual two was. Okay, five and six. So individual three had parent five and parent six. Over here- (Brady: Number five's been busy.)
- I know! There's some scandalous story there we're not privy to. Okay, person four... three and six. So let's do that. Three and six. And person five, okay. Six and two. Six and two. And individual six. Who are they related to? Six and four Six and one, two, three, four. Okay. So now I should make a note of who's related to who actually. So this person is related to 1 in the present day. This person is related to person five. This person is related to person four in the present day. This person is related to person six. This person, right. Person five, who's been busy is related to one two and three. Person six - three, four, five, and six. Okay, I'm gonna take this back of generation and see who the grandparents are. Let's do it. This is tedious, you'll speed this up won't you? Let's see who the grandparents are related to in the present day. Person - individual one is related to all these people via this child here and also related to personal five. So that's okay so that's still three, four, five, and six. This person is also related to three, four, five, and six via this child. This person is related to individual six. And that's it. This person is related to one, two, and three. This person is related to individual four, and so I'm going to take this back another generation, let's keep going. [fast forwarding noises] Okay, now, hm, something's happened in this generation that didn't happen before. These two people have no kids. They're not related to anyone in the present day. I'm gonna say N for no one. This person had three children, related to all these people, all those people and all those people. Now- (Brady: They got the set!) They've got the set. One two three, four five six. They are related to everyone in the present day. Mmm, that's interesting! What about the other people? This person is related to what - one, two three, four children. Not the full set. This person is related to six, one, two, and three, one again, five. And this person is related to person four. So we've got someone related to everyone in the present day. This generation, or this individual, is called our most recent common ancestor. This person is the first person, if we all trace our family tree back, it would be the first person who's related to everyone in the present day. (Brady: I feel a real warmth towards them!)
- I know, I know, this is a grandparent to all of us, isn't that nice? That is nice. Let's go a few more generations back. So we've got five and six. Now this is the person over here who had no kids. Okay, five and six. Let's do it! Five and six. (Brady: Don't really care who these people are related to, do we?) Almost inconsequential. [Music] I have one, I think I may be one generation away. [Music continues] And this is the generation I wanted to get to. This has a name. This is called the Identical Ancestors generation. So what happens at this point is either you're related to everyone in the present day or you're related to no one in the present day. And that's always what's going to happen. So if we keep going back we get to a point with the first common ancestor, and then that kind of increases as we go back and we get to a generation where they're related to everyone, or at some point the line died out and they're related to no one. (Brady: James, it feels like there's one flaw in this argument though. Your dice are very...) (arbitrary and very fair.)
- Yes. (Brady: Whereas, you know, people like you and me are never going to marry a princess.)
- [laughing] Yeah, absolutely. (Brady: So there are a certain kind of - there are certain people above who there's no chance they'll be my parents.) (Whereas your dice, everyone's got a chance of being my parent.) - You are absolutely - you know, you've noticed that problem. So this is just to illustrate a point for now, and what I'm trying to illustrate here is to show you that there will be a point where we have identical ancestors. And also, I think it's kind of surprisingly recent. I mean we only had to go back one, two, three generations to get our most recent common ancestor, and then I went back another four generations, and everyone was related to me. So the point I'm trying to make here is it doesn't take a very long time for us to be all related to the same ancestors. Now you were saying this is not true to life and I agree. This is not true to life because in this example I'm just as likely to have two parents who are from Paris as to have one parent from Iceland and one parent from Australia. Which is not real life at all, and there are other problems with this model. We've got a constant population as well. We can talk about that. So it's not a growing population. And also we had this strange problem. We had the virgin birth, that came up a few times. Well, we've got, we've got small numbers here. If we were talking about a population of millions, then that would mean that's not going to happen. So maybe that would be more accurate. (Brady: Once every two thousand years maybe.)
- Yeah, yeah. If we just play with the model first. There was a mathematician from Yale, Joseph Chang, who looked at this model and he came up with a way to estimate when the most common recent ancestor would turn up. And then the identical ancestors. So our most recent common ancestor, so the estimate for working out that. He called this Tn, so it's the number of generations you need to go back based on the population, which is the n part of this. And he wrote it out to be when it's the solution to this formula: 2 to the power Tn equal to n and if you're familiar with logarithms that's not too hard then. If you're happy with that kind of thing, it would be this: The logarithm to base 2 of n is the most recent common ancestor generation. In my example n was 6, it was to the population of 6 people. So if I did that it would be log base 2 of 6 which is 2.58. So I'm expecting this to happen three generations back. And I think that's exactly what we got in our experiment. Three generations back was the most recent common ancestor. For the identical ancestor generation, Joseph Chang called this Un and to work that out, it's gonna be equal to 1.77 times Tn. My example then, I know what Tn is so it's just 1.77 multiplied by that figure I've already got which is 4.58. So I think I was a bit unlucky with the example I did, I think it happened seven generations back, but you can see it was roundabout right. Now... (Brady: You know what I'm going to ask you to do?)
- What? (Brady: Plug in the population of the world!)
- Perfect! Exactly, now we've talked about the limits of this model, right? So you need a freedom of movement, or freedom to move between social status. So I'm just going to work on something a bit smaller to start with, we'll go up to the world, I'm coming to that. I'm gonna work on the population of Europe, and maybe this is going too big itself but let's say population of Europe. Let's imagine there was free movement in Europe. So- (Brady: [laughing] Yeah. Nice timing.) [Laughing] So what is the population of Europe? I know this, it's seven hundred and forty million. That's the current population. Okay. Let's go back to our most recent common ancestor. Well, we just put in that figure. It's going to be 29.5 generations. I used the current population of Europe to work that out. (Brady: That's quite - that's 20, 30 generations.) Yeah, thirty generations back. Yeah, I reckon that's about nine hundred, thousand years ago? I think we can have a more accurate answer for this because, do you remember my model had a stable population? It wasn't a growing population. If we want to study a growing population we should use a figure for the population at the time of the most recent common ancestor. That would do it. Now, I know it's going to be about a thousand years ago, so now I can sort of use that figure and get a slightly more accurate answer for this. So I'm going to do that. Go a thousand years back and the population of Europe was about 65 million So it's log base 2 of 65 million. This is the sort of answer I'm expecting and that would be about 25.9 generations back. So twenty six generations back. Yeah, nine hundred years ago, something eight hundred years ago, something like that. And then, our identical ancestors. How far do we have to go back? This means everyone in Europe, and you know, there are things you can argue about this. We're doing this for fun. Everyone in Europe would be descended from this generation; from everyone who was alive at this generation, if they survived at all if their - if their family tree did not die out. (Brady: So presumably that would include your Royals?) Including the Royals, exactly! So the royal families survive because we can trace their tree. We can trace their family tree back. So therefore any royal family should be related to all of us, and what generation is that? So it was Un in this system, which was 1.77 times - I'm gonna use that figure, twenty-six, isn't it, really? 25.9. And that generation: 45.9. So about forty six generations ago, so I'm thinking that's about 1300 years ago, something like that? So who was king 1300 years ago? It was Charles the Great, or Charlemagne, he's also known as. He ruled over what remained of the Roman Empire, and then his kids kind of broke up Europe to become the current royal families of Europe. And we can trace that - trace that family tree down to the current royal family. That means that everyone who has European ancestry alive in the present day is a direct descendant of Charlemagne. (Brady: Nice.)
- Nice! (Brady: But not Edward the Third, or whoever you said?) Not necessarily Edward the Third. So if we went back to our most recent common ancestor, well, that's nine hundred years ago, something like that. And we don't know who that is, you know, that could be a peasant or royalty or someone in between. We don't know who that person is. But we do know that there is a point where we're related to everyone, about 1,300 years ago.
(Brady: Wouldn't it be great to go back in time and tell that person of their special role?) So, well, think of it this way. Play this forwards. Everyone alive today, if their family tree survives, will be related to that generation in 1,000 years time. And a direct descendant, or a direct ancestor to that generation. And now I was talking about Europe there, because just to keep it kind of contained. So you could do this for Asia and Africa and you'd have the equivalent problem. You would have the equivalent of a royal family. You asked me about the world, and that becomes more complicated because there's not free movement. And so this is what they did. They broke up the world into continents, into countries, into towns. They looked at historical data, so they could look at the populations based on historical records. They looked at migration rates from country to country, from continent to continent. And then to see what is the generation that contains our most recent common ancestor, what is the identical ancestor generation. Now the problem with this model is the migration rates. The populations are historical record, we've got things for that. The migration rates we don't have figures for that so you kind of have to guess and see what happened. Our most recent common ancestor could be anywhere from five hundred years ago, this is for the world, to three thousand years ago. So somewhere between that. It turns out in their model that person always came from East Asia. Just because of the way East Asia is connected to the rest of the world. And then the identical ancestor population was somewhere between four thousand years ago and seven thousand years ago. Which is relatively recent. If we consider this idea of tracing our family trees back through our mothers or through our fathers, which was this idea of mitochondrial Eve or Y chromosome Adam, right? Our most recent ancestor tracing back through our mothers or fathers was about two hundred thousand years ago. But if you take that restriction away, we're just tracing our family trees back normally, then yes, about five hundred or three thousand years ago, somewhere there, is our most recent common ancestor of the whole world. (Brady: So if I went back to seven thousand years in a time machine,) (every single person on the planet either) (leads to a dead end and has no living ancestors or, is related to me?) Exactly right. In fact, the paper that they published in Nature, you know, it's, you know, it's a maths paper, but then they ended it in this lovely way! There's a lovely sentiment at the end of the paper, which I'm just going to read, if you don't mind "No matter the languages we speak or the colours of our skin, we share ancestors who planted rice on the banks of the Yangtze, who first domesticated horses on the steps of the Ukraine, who hunted giant sloths in the forests of North and South America, and who labored to build the Great Pyramid of Khufu." And that's such a beautiful sentiment to end with. [Preview] So the average number of kids well, I just add up the values here and divide by six. Nine out of six would be the average. It's greater than one.
https://xkcd.com/1545/
I linked to the video to the point when he practically quotes the Strength in the comic.
this feels very wrong to me. I mean didn't original Australians and Americans break off the rest of humans around 7000+ years ago? so there is no way 500-3000 years is what links me (a middle Eastern person) to a native tribe in Brazil.