Everyone on Earth is your cousin (2015) | Hacker News Reader

Everyone on Earth is your cousin (2015)

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159 pointsmorkin80 comments

There are a few particularly interesting points when you go back up your ancestor tree. First, there is a point where some ancestor of yours is an ancestor of everyone else currently living (and so will also be an ancestor of everyone else to come). This is the "most recent common ancestor" point.

Go farther back and you reach the "identical ancestors point" (also known as the "all common ancestors point" or the "genetic isopoint"). The is the most recent point where everyone alive either is an ancestor of everyone currently living or has no living descendants.

Even farther back is the "Mitochondrial Eve" (or "matrilineal most recent common ancestor"). This is like the "most recent common ancestor" except only counts matrilineal descent. I.e., it is the most recent point where there is a woman that all currently living people can trace their ancestry to entirely through women.

There's a similar point for the "Y-chomosomal Adam" via patrilineal descent.

It is believed that the identical ancestor point is less than 15000 years ago. Note that this is after the Neanderthals went extinct. It follows that since there are people alive today with Neanderthal ancestry, there must have been people alive at the identical ancestor point who had Neanderthal ancestry and who have descendants alive today, and so by the definition of the identical ancestor point everyone alive today is a descendent of all such people. Hence, we can conclude that every current human has Neanderthal ancestry.

Same goes for the Denisovans.

Note that this doesn't mean that everyone today has Neanderthal or Denisovan DNA. We only have enough genes to have genes from all our ancestors back for 15 or so generations. Because of this you can have someone who is an ancestor of yours but you have none of their DNA.

Thank you, I learned a lot from your comment.

It also occurred to me that since only about half of a parent's genes are passed on, a person can have had Neanderthal ancestry and for whatever reason the Neanderthal genes were not passed on.

I think it is better to speak of uniquely Neanderthal genes. Our genome must have been almost identical to the Neanderthal genome, given that interbreeding was both possible and that the hybrid offspring remained fertile. So it is likely that many people alive today do indeed have genes from the Neanderthal line, but those genes are either identical to human genes or so close that we cannot distinguish their Neanderthal original from ordinary variations/mutations.

Another thing I find interesting is that your family right now are the most closest humans related to you. When you go back in time or forward in time, the relatedness dilutes.

Even then, you and your sibling could, statistically, share zero genes (you each get 50% from each parent and it is possible you each got a different 50%). Your own parents and children are the closest relatives you have since you are guaranteed to have 50% of your parent’s genes and same with your children.

Identical twins are truly special in that sense.

> share zero genes

That would be impossible, unless one of you is some kind of bacteria. And even in that case I doubt it. According to Wikipedia[1] (yes, I invested some time to refute a random stranger on the internet, well, maybe a cousin) there is something like 0.1-0.4% of genetic variation between humans.

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

The context here is familial relations, while it's true all humans share dna we ignore that when discussing whether someone is related to another.

Humans have approximately 30,000 genes. These genes are sequences that appear in our DNA which is divided up amongst our 23 chromosomes. Offspring receive these genes from their two parents so during meiosis we receive some genetic material from our mother and some from our father. There is about a 50% chance of receiving the mother's gene and a 50% chance of receiving the father's gene for each of the 30,000 genes involves. (The details are more complicated, see [1].)

So yes, statistically one could with probability of something like 1/(2^30000) receive a complete different set of genes than a sibling. In the real world, one will always share around 50% of ones genes with a sibling.

[1] https://www.genome.gov/genetics-glossary/Crossing-Over

The number of crossover events is 55-75 not once per gene, your numbers are off by a few orders of magnitude

> We only have enough genes to have genes from all our ancestors back for 15 or so generations.

Isn't the more relevant number the 46 chromosomes? So we can't even share DNA with everyone six generations back.

Genetics are much more complicated than that. Processes like recombination means there’s much more options to mix and match genes.

> Isn't the more relevant number the 46 chromosomes?

Not so much. Because chromosomes recombine during meiosis (sex cell differentiation), so people never pass on the chromosomes they received from their individual parents fully intact to their offspring.

I’ve read various studies that believe that our most recent common ancestor lives 2000-4000 years ago.

That seems a much shorter span of time for civilizations to spring up. Egypt, Iraq, India and Europe has history which was already divergent at that point of time.

Basically all you need is a single person traveling to a new area and reproducing and people travelled a lot more than our provincial thinking assumes. Just think of Assyria taking entire civilizations and transplanting them in new areas. The mongols, German hordes, Vikings, etc. raping and pillaging around the world. Polynesian sailors having contact with both SE Asia and South America. All the European colonization. Etc.

Not true. Australian aborigines split off 40k years ago. Now, if somehow we interbred with all of them, so that no pure aborigines are left, in a 100 years we move the line to a date that resembles what you suggest. We have to do that every remote tribe on earth. Or if for some reason they are killed.

Isolated populations never remain fully isolated. If Aboriginal Australians managed to reach Australia tens of thousands of years ago, it makes no sense to assume that nobody ever followed them. It's far more likely that there was constant low-level contact with Austronesian peoples – even if it didn't occur in every generation or every century. And it's also quite likely that some lost sailors ended up in Australia over millennia, and some of them had children.

If the level of contact is low enough, it won't leave any measurable genetic traces. After all, if you go back sufficiently many generations, most of your biological ancestors are not your genetic ancestors.

Are you saying not true without even reading the studies, speaking from scientific knowledge, or speaking off the cuff?

I was wrong. Just checked Dawkins’ “ancestor tale”.

Maybe I'm stupid but I'm not sure I understand the difference between most recent common ancestor and the identical ancestors point. Can someone explain differently?

From my reading of the above, the “most recent common ancestor” is a single individual who acts as a common ancestor to all alive today

Whereas “identical ancestors” is a time period where everyone alive is an ancestor to those living today. So a group of ancestors are being selected — rather than just the one. So this should generally always be closer to now than the “single recent ancestor”, simply by virtue of allowing the ancestor tree to be more splayed out.

However, my understanding of the latter must be wrong, because yesterday would always be the most recent time period holding true to that definition — or if it only counts if none of the people alive today are alive in the identical ancestor time period, then it’s always going to be today - current oldest human’s age - 1 day.

My reading was that the “identical ancestors point" is the point at which every person is either: 1. an ancestor of all currently living people; or 2. an ancestor of no one currently living (ie their line died out).

Alternatively, it’s the time when all currently living humans have exactly the same set of ancestors.

Whereas “most recent common ancestor” means that the intersection of ancestries of all living people is non-empty. (That intersection being the common ancestor)

During the "most recent common ancestor" period, as you said, there's a single individual who acts as a common ancestor to all those alive today. Let's for sake of argument say that person is Genghis Khan, that Genghis Khan is somewhere in every current living person's family tree. How about Genghis's parents? Mr. and Ms. Khan (actually Yesugei and Hoelun) are surely BOTH common ancestors to everyone alive today. And surely Grandpappy Khan and the other three grandparents, and so on, going back. That ancestral tree keeps growing and eventually, you'll get to the point in the past that everyone alive at that period is an ancestor to Genghis Khan. Which means they are all also in our family tree. Therefore we all have an identical looking family tree from that point backwards.

MRCA: Take every current person's family tree, who is the most recent person who is in all of them? This doesn't mean there was only one ancestor around at the time, though if all life came from the same cell that is of course true if you go back that far.

IAP: For any given time X, every person at time X is either an ancestor of all current people, or none. Take everyone's family tree, and since it can't be size 2^x generations back, the overlaps eventually mean that all those people at time X who have a current descendent actually have everyone alive currently as their descendant, and everyone else at time X is the ancestor of nobody currently alive.

At any given moment in time, let n be the number of people who are an ancestor of everyone alive in 2021 (or 2022!).

Right now, n = 0 because there is nobody on earth that is the anscestor of everybody else.

If you go back far enough, you'll get n = 1. That's a single person that is an anscestor for everyone alive today. That's the most recent common anscestor. Other people then were anscestors to only some people alive today.

If you go back further, you'll get n = total number of people on the planet at the time. Everyone on earth is an anscestor of people alive today.

Except, wait, that's not true! There will always be some people alive who aren't anscestors to anyone alive today. Maybe they simply didn't get lucky at all in their lifetime, or were infertile. Maybe a collection of people only bred within a community (tribe, city, etc) which then got wiped out in a war. Maybe something more complex happened. So n=1 is possible, but n=everyone never happened.

So, totally ignore all the people who aren't anscestors to anyone in 2021, leaving only people that still have at least some anscestors today. Then n = 1 is (still) the most recent common anscestor. And the earlier date, n = everyone (that we care about) is the identical anscestors point.

Ah makes sense, I think the use of present tense in the original explanation was throwing me for a loop.

Another way to think of it is at any given time in the past, you can put any given person into one of three classes:

1. Nobody alive today is descended from them,

2. Some people alive today are descended from them, and some people alive today are not descended from them,

3. Everybody alive today is descended from them.

Go back a short time, and everybody is in groups #1 or #2.

Go back farther and you reach a time where there is someone in group #3.

Keep going back and you reach a point where nobody is left in group #2.

The most recent common ancestor point is when group #3 going back gets its first member.

The identical ancestor point is when group #2 going back loses its last member.

>Note that this is after the Neanderthals went extinct. It follows that since there are people alive today with Neanderthal ancestry, there must have been people alive at the identical ancestor point who had Neanderthal ancestry and who have descendants alive today, and so by the definition of the identical ancestor point everyone alive today is a descendent of all such people.

Not by definition. Adam is older than Eve which suggests we are descendant from multiple mate's of Eve. Some might have had neanderthal ancenstry, some might have not.

"our own personal history — which we really should know quite well..."

I have to admit I don't really get this. I know this is a common sentiment, but I'm just not really interested. Every now and then my mother will drop a tidbit like "when I was horse riding around the pyramids..." and it'll be interesting. But in practical terms there's an infinite amount of things she could tell me and I'm not going to hear it all before she dies. I know there are others who are fascinated by these kinds of things, and I have nothing against that, but it mostly leaves me cold.

It's an interesting juxtaposition to my interest in history - some of her stories about being sent to live with relatives in Ireland during WWII tie in nicely to my interest in that period - but I don't find it particularly enlightening on a personal level. I suppose it was best expressed during a series of programmes on Scotland by Jonathan Meades, where he's talking about the ancestry industry that's so strong there - "why should I be interested if my great, great, great grandparent with rickets hobbled alongside this river with their sheep?"

Pro tip, get the old folks talking, and take out your phone to record. Whatever they're talking about, even if they're talking about nothing at all. They'll all be gone soon, and having video of your boring everyday interactions with them is better than having only your memories of them.

This is probably one of my greatest regrets with my grandmother.

I was planning to do exactly this for quite a while but life had other plans, she is gone now and although I have great memories of her, I do regret not having a video record of her story telling to be able to share with her great-grandkids.

Oh, that really hurts. I'm lucky my grandpa's sister is still around. I should go see her more.

During Thanksgiving I found out my grandpa had a rebellious streak. He quit a steady high-paying job with an American bananero to live in the jungle by himself for a bit. Apparently he had a really tense relationship with authority, which I see in my mom, one of my brothers and definitely in myself.

During his time living out in the wild, he constructed platforms in trees to sleep on. His outpost was near the villages his family lived in, so his main task out there was to keep the area free of leopards. I learned that one of my aunts in Central America might actually have photos of my grandpa as a young man with his leopard trophies!

My God. The things I missed hearing. Era muy chingon mi abuelo.

My father died 12 days before my 13th birthday, cancer. My 7th grade tech teacher (also sadly now dead from leukemia) sent me home with a camcorder to interview dad, to record memories, because his father died young too. What did I do? I sat in a chair and pointed it at the tv and recorded episodes of Battlestar Galactica (1978) reruns on tv...

Sigh. Although, dad was pretty sick then from both the cancer and treatment and I'm not sure I would have wanted to revisit those videos anyway so maybe it's a blessing in disguise. As it stands though, I only have one recording of his voice - an answering machine recording and I do think it would be nice to have more of his voice. I guess I'll have to wait for time machines.

interesting counter intuitive plot

methinks a microphone would often be better suited then, unless voice is also ruined by the disease

Why? You'll be forgotten about too in about 40 years

You are right, so why don't we all just kill ourselves? Nothing lasts anyways, so what's the point of all this really. Except of course, if you learn to appreciate what you have right now...

> […] and having video of your boring everyday interactions with them is better than having only your memories of them.

How comes? To me, the most valuable things from the past are the memories. Not photos, video and stuff.

There will come a time when you realize you can no longer hear how someone's voice sounded when you think about them. It can be comforting to go back and hear them in their own voice again.

My wife and I found out we are 10th cousins. She is not amused when it is sexy time and I call her cousin. LOL

This article made me wonder about an idea I’ve been thinking about for years.

There are people who have prosopagnosia, also known as face blindness, the inability to recognize familiar faces. I’m not exactly a super recogniser, but I have an unusual ability to remember a face.

Beyond these two extremes, would it be possible to recognize a face you’ve never seen before as a possible relative, and has such a thing ever occurred, and what is the mechanism behind it?

I’ve read stories about putative pheromones and such, but that seems to be somewhat on the fringe.

So to further refine my question: can we recognize (visually or otherwise) strangers as potential relatives in some way by sense perception, if they are closer to us on the cone of ancestry?

Somewhat related documentary: Twinsters 2015 https://www.imdb.com/title/tt2980626/ It's good.

On some level, yes: we can generally distinguish human faces from chimpanzee, gorilla, and other primate faces. In general, though, our facial recognition has some quirks that make more fine-grained identification of relatedness hard. For example if I shave my beard it takes people a moment to recognize me, especially if I do not give them any clues. Also note that if we had a reliable way to identify degrees of relationship tribal marks would be far less common since tribal affinity could be detected automatically.

In general ape facial recognition is oriented toward familiarity, not relatedness. This makes sense given the patterns of social behavior in apes -- fission/fusion social groups, individuals leaving their childhood group and joining a new group as adults, etc. It also makes sense given that establishing trust (or degrees of trust) is one of the primary functions of facial recognition, and people often betray the trust of their close relatives. Familiarity is also more general, since we are often familiar with our close relatives but can also be familiar with others, and the complexity of ape social groups requires a more general kind of recognition.

> So to further refine my question: can we recognize (visually or otherwise) strangers as potential relatives in some way by sense perception, if they are closer to us on the cone of ancestry?

Like being able to tell someone's race? It's imperfect and fuzzy at the edges, but socially constructed racial categories more or less correspond to clusters on the human genetic principal component analysis graph:

https://commons.wikimedia.org/wiki/Category:Principal_compon...

Im not sure if I understand you correctly. But that’s not uncommon where Im from. People will sometimes stop to ask you if you’re related to X sincerely you look familiar. The person doesn’t have to be a relative.

Example: I’ve had a 4th grade teacher recognize my uncle in a setting totally unrelated to school. He happened to meet my uncle and noticed a resemblance.

> Now I feel special and important and also I feel irrelevant and meaningless.

There's an infinite number of ways to end up at this feeling+realization.

Personally, I reached this when I got interested in cosmology (PBS Space Time!!).

I invoke Nihilistic (existential nihilism) ideas. Because it's not hard to end up at the conclusion that everything is meaningless - you create your own meaning.

I recognize lots of problems attempting to apply this at scale, but it works for me personally.

This seems more like a perspectivism, egoism, or absurdism than nihilism. Ultimately, nihilism is the position that even any meaning you create is likewise inherently meaningless. To create your own meaning, and maintain that it is meaningful, is a refutation of nihilism, not its embrace.

In the strictest sense, yes you're right. But there are so many "flavors" in popular culture.

For me, Nihilism is the input. i.e. everything is meaningless. But the output, i.e. what do you do, is separate.

There is nothing more freeing than embracing nihilism. We're just sentient space dust, after all.

Totally. The concept of heat death made everything feel pointless to me (that was my moment).

Heat death is well over 10^106 years away[0] but for some reason i was like wtf... nothing matters.

[0] https://en.wikipedia.org/wiki/Heat_death_of_the_universe#Tim...

I find it it incredibly funny to worry about the heat death of the universe. That's so far beyond our scope of comprehension and the limits of the lifetime of the entire human race it does not matter in the slightest. It feels like the most absurd form of existential egotism.

Yeah that's fair enough. I care more about the end of my consciousness and my own dust turning to dust yet again than the heat death of the universe, something that's so far away, and asymptotically won't ever happen. Is it really the end if nothing can "experience" it?

> I care more about the end of my consciousness

Oh yeah, that one is very personal and I continually struggle with it.

Your Highnesses, Dear Cousins, Peers.

Allow us to draw your attention to the state of intellectual exchange between our honorable houses, which we have enjoyed in the past.

https://nautil.us/issue/56/perspective/youre-descended-from-...

https://www.scientificamerican.com/article/humans-are-all-mo...

Discussed here: https://news.ycombinator.com/item?id=24686904

Almost every country was very homogeneous just 50 years ago, so your family tree wont branch out like that normally. USA is a bit different since it is a nation of immigrants, but mostly people barely even left their villages historically.

Also, if you go back a few hundred years there were relatively so few people on the Earth. I bought First Wife a posey ring from 1600s England. I was interested to know just how many people were around then. It was about 5% of the current population. The world was empty.

Well. There were fewer people, yes, but they also moved around a lot more. It's only comparatively recently that we've gotten stuck in our places and social structures.

What? I can't tell if this is a joke but the average person in the 1600s moved around a lot less than the average person today. I wouldn't be surprised if 80% of them never left a ten-mile radius.

Which persons are you referring to? People in the Americas, in Australia, in Africa as well as probably other places I'm forgetting about easily traveled hundreds of miles and both shaped and joined communities other than the ones they were in before.

I'm talking about the overwhelming majority of people who did not have a nomadic lifestyle or typically travel long distances.

By 1600, most of the world's 500 million people lived in what we would recognize as settled communities in modern-day India, China, Europe and the near/middle East [0].

Fewer than a million aboriginals lived in Australia and a few million in the US [1]. Nomadic lifestyles simply can't support anywhere close to the density achievable by even subsistence farming.

[0] https://en.m.wikipedia.org/wiki/List_of_countries_by_populat...

[1] https://en.m.wikipedia.org/wiki/Population_history_of_Indige...

People in 17c England didn't move much.

It won't branch out all the time, but it doesn't matter much: People staying in one place makes them quickly "saturate" a location. The occasional migrant from the local area then quickly makes it spread outwards in a new area. Few places are so totally isolated that this wouldn't happen.

Not just the USA, the whole American continent is one big exception to that homogeneous countries rule. But if you were to single out a single country, it should probably be Brazil instead, being by many accounts the most heterogeneous country in the world. Fun fact: in the fake passport circles, "Brazilian" is a popular go-to nationality because no one will question a Brazilian nationality based on your face/race/color.

https://archive.md/URif7

There's a link to the original article at the top of the page: https://waitbutwhy.com/2014/01/your-family-past-present-and-...

> Writing this has really hammered home the point that humans are mainly a temporary container for their genes. In 150 years, all 7,100,000,000 people alive today will be dead, but all of our genes will be doing just fine, living in other people.

I really like that takeaway.

Assuming life had a single origin—which is the accepted version of events—every organism on earth is your cousin. You have a common ancestor with every bacteria in your gut, and with the the animal, or vegetable, fish or fungus you just ate.

Dawkins' book "Ancestors Tale" is all about this.

First cousins share 1/8 of their DNA, which is sort of meaningful. Second cousins share 1/32 of their DNA or about 3%, which is really marginal in terms of their being any resemblance or affinity due to DNA. By the time you get to third cousins the shared DNA is down to 1/128 or less than 1%.

So I've lost interest in tracking down any relatives beyond second cousins.

I'm very ignorant about these matters but I thought we all shared the vast majority of our DNA? I mean as humans are we not all 99.9% the same ... DNA wise?

What does the 1/8 mean in this context?

he's probably talking about snps, single nucleotide polymorphisms, which are pretty much the places where human dna is different from one another.

A child inherits half of the mother's DNA and half of the father's DNA. This is because in somatic cells chromosomes come in pairs, but when sperm and eggs are produced, the pairs divide and each sperm or egg contains only one chromosome from each of the 23 pairs.

Therefore, given that you have received one of each pair, the probability is 1/2 that your sibling received the same one of the pair. Thus, siblings share 1/2 of their DNA on average.

When you get to first cousins, each line of descent from the common grandparents is diluted by 1/2 from the grandparents that they do not have in common.

Thus Nth cousins share on average 1 / 2 ^(2N+1) of their DNA in the sense that the shared DNA is inherited from their common ancestor. This is the only part of their genome that would cause their phenotypes to be similar. Any other similarities between cousins is by chance or because their relatives may have married into similar ethnic groups with shared deeper ancestry.

When talking about relatives the fraction refers to the amount of variation in the population.

To simplify, say every 100 bases are random and all humans share the 99% that are the same.

A brother and sister have 50% in common out of the 1% that varies, so they are 99.5% identical relative to whole genome or 50% relative to the variation.

It depends on what population you use as a reference too. Relative to white people, two average white people are unrelated. Relative to the 'average human' they are as related as uncle/nephew. Relative to Bushmen/Pygmy/Andaman islanders, closer still. Relative to a banana, much closer than siblings (in the usual measure) though not quite identical twins

I've grown to see not only humans but also animals and plants to be on the same tree of life.

Some natives in South America call the animals our little grandmas and grandpas, and I can relate to that.

It's typical for one to be treated by their children the same way they had treated their own parents and grandparents.

I wonder what this means for us.

What happens if your parents are first cousins? You don’t have as many ancestors as the article assumes. And it’s only now that people are so connected that such a situation can arise, but earlier people used to marry mostly within their local communities, so each spouse would share many of the same ancestors as the other.

This is described in the article, see “pedigree collapse” therein.

Oh thanks

Come on, I didn't hump that many people.

Also, a large proportion of the world's population may be your sibling-in-law (https://xkcd.com/2040/).

"sweet home alabama..."

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