Thousands of amateur genealogists have contributed to a huge database of family relationships, including genetic analyses. What does this teach us about human populations and evolution?
It may seem like a ridiculous question to ask whether you are a descendant of Charlemagne, who was crowned Emperor on December 25, 800. If you live in Asia or Africa, or your ancestors are from Asia or Africa, then you are probably not a descendant of Charlemagne.
But if any of your ancestors lived in Europe, especially western Europe, then it's almost certain that Charlemagne is one of your ancestors. No matter where your ancestors are from they probably share a common ancestor with everyone else from that region. What's surprising is that many of those common ancestors lived only 1200 years ago.
I'm talking about big regions here, like most of Europe or Asia, or Africa. There's a remarkable amount of inbreeding among human populations at that scale. It's a good example of how evolution works. It's populations that evolve.
Remember that it's populations that evolve, not individuals. With only a few exceptions, species are subdivided into numerous populations with restricted gene flow between them. The sub divisions range from very large group called races, or subspecies, to progressively smaller populations down to local demes or extended families. In small populations, alleles can become rapidly fixed by random genetic drift but the existence of these populations means that it is much more difficult for these alleles to spread to the rest of the species. What we expect to see under those conditions is races or demes that differ substantially in their allele frequencies.
The explosion in amateur genealogy in recent years has highlighted these kinds of population structures in our own species. More and more people are putting their genealogical research on publicly accessible databases such as ancestry.com and many others. The collective result of these, mostly amateur, investigations is remarkable. It means that every one of us can make a family tree.
Well, perhaps not everyone. There's a huge bias towards Caucasians in the genealogy databases. There are many reasons for this bias but we won't go into them in this post. The important result is that we can all learn something about human populations from this data even if it doesn't include your own ancestors.
The other recent development is the increasing number of people who are having their DNA analyzed and posting the results online. This is much more important since people all over the world are participating and we will soon have a good picture of the genetic structure of today's populations. This complements the family tree data in the same way that gene phylogenies complement the fossil record.
What about Charlemagne? Amateur European genealogists have to do a lot of work to document their ancestors back four or five generations. This takes them to the 1800s (30 years per generation).1 At that point in time they have 16 or 32 direct ancestors and chances are they'll be able to hook up with others who share these ancestors. The farther back you go on your own, the greater the chances that someone will have researched your ancestor.
The idea that many of us are related to Charlemagne is not new. Here's what they say on the Genealogy of Presidents website.
Genealogists have mathematically demonstrated how all Americans of European descent must be related to Charlemagne. In this regard, genealogists have established the exact lines of descent from Charlemagne for 14 U.S. Presidents. Two of these are President George W. Bush and his father President George H.W. Bush. Other Presidents whose descent from Charlemagne have been traced include: George Washington, Ulysses Grant, Franklin Roosevelt, Teddy Roosevelt, and Gerald Ford. To demonstrate how we are all related, the New England Historical Society has researched the genealogy of Barack Obama and determined that on his mother's side he is related to six other previous presidents: George W. Bush, George H. W. Bush, Lyndon Johnson, Harry Truman, Gerald Ford, and James Madison. Presumably, if Barack Obama's ancestry on his mother's side could be traced far enough back, he also would be shown to be descended from Charlemagne. Meanwhile, on his father's side, we are all related to President Barack Obama since anthropologists have determined that all modern humans are descended from a common African ancestor.
If you examine the List of United States Presidents by genealogical relationship you'll see that 19 US Presidents are descendants of British royalty and therefore, almost certainly, descendants of Charlemagne. Note that US Presidents are not royalty, they are, to all intents and purposes, ordinary citizens, just like you and me.
It's almost trivial to find connections to the US Presidents if you have ancestors who settled in the British colonies in the 1600s. I'm related to George Bush, for example, through the Shermans of Rhode Island and Connecticut. The good news is that I'm also related to Winston Churchill though the same family.
The amazing thing about genealogy is how closely related everyone is once you start looking. This isn't so amazing to population geneticists.
It's not so hard for North Americans to find European ancestors but many lineages terminate because parish records have not been preserved and because there are no other sources for the ancestors of average citizens. But every now and then you'll stumble upon lineages that have been well researched. Among my own ancestors for example there are half a dozen lineages that reach back to the 1400s and beyond. All I did was find the connections to those lineages.
The history of European nobility is well known. Chances are, you have at least one ancestor who connects to the various Dukes, barons, Counts, and Knights and their spouses in medieval times . A large percentage of the nobility of the European nobility can claim descent from Charlemagne. He had 20 children.
With a little effort, almost everyone of European descent can find the path to Charlemagne. If your ancestors are from England or Scotland your connection often runs through William of Normandy and a bunch of other tourists from France who visited England in 1066. Be careful, though, because there are many incorrect genealogies on the web and you'll need to do some fact checking. I found three different connections to nobility but two of them were figments of someone's overactive imagination. [See My Family and Other Emperors for my relationship to Charelmeange.]
Expert genealogists, as opposed to amateurs, are very frustrated by these errors on the internet. Because of the nature of the databases, it's very hard to remove errors once they start being incorporated into various genealogies.
The fact that all Europeans have several recent common ancestors tells us a lot about the genetic makeup of this population. It is quite homogeneous and there's a lot of inbreeding. It seems to be extremely rare to discover a non-European ancestor once one goes back a few hundred years. (It's much more common in recent times.) I presume this lack of outbreeding also applies to Asians, Africans, and all other groups.
Given that the average generation is 30 years2, if you go back to 800 that's about 40 generations. Potentially you have 240 ancestors. That's more than 1 trillion ancestors alive in 800. I don't know what the population of Europe was in 800 but I strongly suspect it wasn't even close to one trillion people. I suspect it was only about 25 million. It's not surprising that you are related to many of them.
It would be interesting to know how many people who were alive in 800 have direct descendants who are alive today. Maybe there's a way of calculating this?
1. In my case it was my mother who did/does all the work. I just surfed the internet using her data.
2. The actual calculated value for my ancestors is 29 years per generation.