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.
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.
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.
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.
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.
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.
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.
Isn't the more relevant number the 46 chromosomes? So we can't even share DNA with everyone six generations back.
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 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?"
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?
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.
For me, Nihilism is the input. i.e. everything is meaningless. But the output, i.e. what do you do, is separate.
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...
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
I really like that takeaway.
So I've lost interest in tracking down any relatives beyond second cousins.
What does the 1/8 mean in this context?
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.
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
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.
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.
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.
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.
How comes? To me, the most valuable things from the past are the memories. Not photos, video and stuff.
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.
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...
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.
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)
methinks a microphone would often be better suited then, unless voice is also ruined by the disease
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.
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.
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.
Oh yeah, that one is very personal and I continually struggle with it.
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...