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Comment by jl6 | Hacker News Reader

If the average age of giving birth is 25, Mark Antony would be about 80 generations ago. With each generation back doubling the number of ancestors (2 parents, 4 grandparents, …), this person has a theoretical 2^80 ancestors - somewhat more than the number of people that have ever lived. So clearly that logic is flawed, and the family tree must in fact be a family web - but potentially a very, very wide one.

I wouldn’t be surprised if a large portion of the population of Italy were also descendants of Mark Antony, albeit without the famous lineage to prove it.

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There also wasn't much mixing of isolated populations of humans, leading to a relatively large amount of inbreeding. Sort of like a graph with clusters of heavily linked nodes and only a few links between the clusters.

https://www.newscientist.com/article/mg22029453-500-inbreedi...

> "“In the distant past, human populations were probably only in the thousands or at best tens of thousands, and lived locally, exchanging mates only with their nearest neighbours.”"

International shipping, and now, air travel, has changed this - the 20th century and the population boom have led to more genetic mixing than at any point in human history.

We have pretty good evidence since 2013 of bands of neolithic humans moving over really tremendous distances. There's good evidence in the Americas of people moving from the Great Lakes down to the Gulf and beyond. Once horses were domesticated in Eurasia, all bets are off and we see mass migration from the steppe through to all of Europe, India, Iran, the Horn of Africa, and other places. This didn't happen in a single life time, but people on horseback with carts really got around.

All of which is true, but Mark Anthony gets us well into the historical period.

We have a pretty good sense from that of who did and who didn't get around.

It's surely the case that the vast majority of Japanese on Hokkaido are not descendants of Mark Anthony. On Kyshu, maybe, the Portuguese contributed some genes there.

We can really only be detailed about this with a Y chromosome for a man, or mitochondrial lineage for a woman, and that only covers the case of lineal descent.

Not only can we not determine with confidence who is or isn't a descendent, even given a complete DNA sequence we don't have: most of those descendents won't have any Mark Anthony DNA at all! Chromosomes are more chopped than sifted, if that makes sense, I'm going on memory here, but somewhere around the 12th generation, we start having phantom ancestors: they existed, but left no record in our genes.

Yeah, of course the math makes sense but one can clearly find pockets of people it likely doesn't apply to. And for sure, trying to point to specific ancestors isn't really possible you don't even need to go back 12 generations in some cases if memory serves.

My main point is that its becoming clear that many supposedly very isolated populations have in fact had gene mixture with outside groups in the not distant past and that there were large pre-modern migrations and mixing events.

If I'm recalling the numbers correctly, there's somewhere between a one in a million and one in a billion chance of not inheriting any DNA from one of your grandparents -- unlikely, but not so unlikely that there aren't dozens or hundreds of people walking around for whom that is true.

My mother’s parents were from a small island community in Norway. They were second cousins.

One time I got drunk and made out with my second cousin who still lives on that same island. My friends and family who witnessed the course of events were merely amused and not at all disgusted.

Inbreeding ain’t going nowhere in coastal Norway!

My (not at all previously related) wife thinks I’m insane that I love telling this story.

2nd cousin relationships are common in most parts of the world, and not viewed with the circumspection that 1st cousin relationships tend to be. You are much more genetically distant from a 2nd cousin than you are from a 1st.

I would say that the distance depends too on where someone is from. If they come from an endogamous community then they are related to other people in their tree through more than just a single branch. Islands, villages, etc. Sometimes it is fine, other times it can be a problem.

While in the US Navy (1977 ~ 1981) I can distinctly remember the unique facial structures of the people in Southeast Asia and being able to tell what country they were from because of this. A couple of decades later with the mixing of populations by various means, and their diet changing in that-time frame, I couldn't reliably tell anymore.

All it took was a single person who was a wanderer from each isolated community. I’ve read a number of articles that estimate, based on genetics, that every person living has a common ancestor who lived 2000-4000 years ago. It could have been a peasant in rural Tibet or a South Pacific Islander or someone(s) else entirely.

https://sci-hub.st/10.1038/nature02842

> There also wasn't much mixing of isolated populations of humans, leading to a relatively large amount of inbreeding.

The genetics of Rome's population at the beginning of the Common Era were almost identical to that of Anatolia's, but just after Antony this began to change significantly due to the migrations that followed the Roman Empire's expansion: https://news.stanford.edu/2019/11/07/genetic-history-rome/

This is the correct answer. The entire population of Europe is about as descended from Mark Antony as that Georgian noble house. Only the Y-chromosome is lineally passed across such long time spans

Does it follow that same would apply for all humans of Mark Antony's time?

Kinda!

This is covered in Randall Munroe's (of XKCD fame) latest book - What If 2; chapter 33 "Ancestor Fraction"

Obviously a human who did not have any children cannot be the ancestor of anyone - this includes the circa 50% of humans who died during infancy, and the 25% of adult humans who did not have children.

Also, for some people who had children the line will die-out; if you have four children all of whom die in infancy, your line dies out. If none of your grand-children have children, your line dies out. Randall quotes a study which estimated that this applies to 40% of all people who ever had children.

So, taken together roughly 25% of all humans who were ever born went on to have children and form a part of the modern human 'ancestor web'.

In Summary: If you picked a random human of any age from the time of Mark Antony there is a roughly 25% they are an ancestor to all humans. If they are an adult that rises to 50%, and if they already have kids it rises to about 62.5%.

Does this take into account geographical limitations? I don't know about today, but if you applied the same analysis to the global population of 1600, it seems impossible on geographical grounds for either Mark Anthony or one of his contemporaries in South America to be an ancestor of everyone alive in 1600.

You’re assuming much more “cross-polination” than actually happened.

Humans didn’t use to mix geographically (hence different races).

And there’s isolated subgroups that didn’t mix or mixed much less (e.g. Jews in Europe)

Is that "are" or "will be" an ancestor to all humans?

No. I don’t know the names of any great first century subsaharan African or Native American leaders, but even 80 generations back there are almost certainly none in my family tree. On the other hand I wouldn’t rule out some Asian steppe leader being in there somewhere.

>Only the Y-chromosome is lineally passed across such long time spans

There's also the mitochondrial DNA passed along female descandants.

Good luck inheriting Mark Anthony's mitochondrial DNA.

The real give away is in the bio: Prince Theodore D. Kopaliani is a member of the Bagrationi Royal House.

All real family trees are not tree-shaped but diamond-shaped due to inbreeding (often very distant), a phenomenon geneaologists call "pedigree collapse":

https://en.wikipedia.org/wiki/Pedigree_collapse

If it's "very distant" is it really inbreeding?

It's inbreeding by the technical definition/understanding but obviously it's not inbreeding from a practical/biologically concerning standpoint.

In that case we're all inbred, so what does the word mean?

> we're all inbred, so what does the word mean

Genealogically, it means a family tree which is not a binary tree [1]. The measure is meaningful over a certain number of generations. Everyone is inbred over infinite generations, assuming a universal common ancestor. That doesn't sap the term of meaning.

Medically, we look at the coefficient of coancestry [2].

Practically, I think we trace back 3 to 4 generations, my source being grandparents (2) is a common word, great grandparents (3) less so but widely understood, and great great grandparents (4) being something few people keep track of.

[1] https://en.wikipedia.org/wiki/Binary_tree

[2]https://link.springer.com/referenceworkentry/10.1007/978-1-4...

The same thing it always meant. Like many things, just because it's a continuum and not binary doesn't mean it's a useless concept.

absolutely not.

What next, we can defend "tall" being anywhere from 1mm to 9 feet because height is a continuum?

Words have meaning so they can be used for communication. If I use the word inbred to mean two siblings having a child and two partners sharing an ancestor 20 generations back, I'm not communicating anything when I use the word inbred.

And pointing out that closeness of ancestry is a continuum is not a defense of using that word in that manner.

I wouldn't be surprised if every person in Europe and every person in the Americas with European ancestry was descended from Mark Antony.

https://www.theguardian.com/science/commentisfree/2015/may/2...

Nice breakdown. Maybe it works the other way too.. that a large percentage of the population alive today can count rulership/prominence in their ancestry.

I speculate that when times were hard for humans in the course of history, those who were better off were more likely to successfully raise kids to adulthood, who in turn had better chances of establishing their own families

Yes, every single person alive that has any ancestry from Western Europe is a direct descendant of William the conqueror and Charlemagne and others. But they are also all direct descendants of the servant who cleaned out their potty every morning (presuming that servant had descendants). Claiming royal descent is not a big deal since we are all descended from everyone that lived back then and has descendants to this day.

https://waitbutwhy.com/2014/01/your-family-past-present-and-...

https://nautil.us/youre-descended-from-royalty-and-so-is-eve...

Furthermore for an ancestor that far back, many of their descendants may not even have inherited any of their actual genes.

Given that we share somewhere well north of 99% of our genes with every other human being that sounds unlikely.

Oh sure, we'll have many of the same genes, but got them from other ancestors.

Given that the lineage has not died out, the average number of ancestors per generation is not zero. If you assume it is 1.2, that would mean about 2M descendants, which seems much more reasonable.

You should read up on family trees. This is an extremely well known thing and you can find a lot of articles that answer this question.

This comment is begging for a link—or at least a description of this "extremely well known thing"

https://waitbutwhy.com/2014/01/your-family-past-present-and-...

https://nautil.us/youre-descended-from-royalty-and-so-is-eve...

https://sci-hub.st/10.1038/nature02842

This is called pedigree collapse.

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