It helps to visualize this more as a mesh than a tree, or as a flowing river. The river divides around rocks and obstructions (those are points of temporary divergent evolution) but ultimately all flows together (convergent ancestry). We are truly one body of genetic material, and yet each is a unique combination of backwards traces.
It's really very cool IMHO.
So like Adam and Eve? :-)
I guess it's kind of like the difference between a permutation and a combination.
In particular, if you have a male ancestor at the Identical Ancestor Point but the lineage from them to you passes through a woman at any point in the family tree, you would not get that male ancestor's Y-chromosome via that line of descent.
Or put yet another way, if you are male, you have 2^N (possibly overlapping) ancestors N generations back, but only _1_ ancestor N generations back that contributed your Y-chromosome. Comparing to a different male, the chance that you share Y-chromosomes is naively something like 1/P where P is the size of the male population at the time, while the chance that you share your ancestor sets is a much more complicated calculation, and the article claims it's ~1.
In the first the path goes through both fathers and mothers. This is easier to achieve, and so you get to it more recently. The second is harder and so happened longer ago.
There was too much time between them.
We focus too much on these two inputs, and forget the other (20) pairs of our nuclei.
And then what would an analogy look for prokaryotes - bacteria, archaea? If my understanding of biology is correct, it would be like an infinitely tall, densely tiered waterfall. There's some forward generational movement, but there's also plenty of lateral ones - exchanging gene packets "at runtime".
Or: it's a DAG, not a tree.
If you look at one generation ago one have 2 * 2 ^ 0 ancestors, at two generations, one have 2 * 2 ^ 1 ancestors, etc. At 27 generations one apparently has more ancestors than people in the world at that time. This apparent paradox stems from the fact that we are heavily inbred.
Thus the article is correct.
I'm not following your point - maybe it's just a linguistic thing. To me, inbreeding implies relation, at least blood-relation, even when there was no other relation, e.g. conquering armies raping and pillaging.
No argument with your math.
Perhaps you're off by a 0 or two...?
The Americas may have been clearly separated for a while, but they have done so much interbreeding with people from other continents since 1492, that the common ancestor is more recent than that.
"Monte Carlo simulations suggest the MRCA was born surprisingly recently, perhaps even within the last 5,000 years, even for people born on different continents."
The book Who We Are and How We Got Here talks about this. When DNA recombines at conception, it only snips and stitches in a fairly limited number of places. It doesn't 'mix' finely like paint. It's more like taking two short pamphlets of ~25 pages, cutting each numbered page horizontally at a random vertical point, and then assembling a new pamphlet of the original size from each pair of pages (pamphlet A's page from above the cut, pamphlet B's from below).
All this to say that if you go back something like 800 years, you have ancestors from whom you didn't get any genes at all.
This means that these infintesimal mixings have even less impact than you'd think. A modern Japanese person could have a European ancestor who traveled to Asia a thousand years ago, but have zero genes from that ancestor. Which means that while that European is technically an 'ancestor', this is just a bit of historical trivia, it means literally nothing about that Japanese person's biology.
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On to the color commentary:
I suspect that articles like this are heavily influenced by the politically-based drive to try to minimize intergroup genetic differences in humans. The reality is opposite the title - humans are far more distinct, especially on group levels, than is commonly understood. The notion that single common ancestors (among trillions) mean people from hugely divergent groups are 'related' in some meaningful way is just exploiting and expanding the ignorance of the public around how genetics actually work.
It's arguably a pro-social thing to do; I'd say I agree with the philosophy here, but that doesn't make it true and the 'noble lie' seems anything but to me.
The genetic evolutionary difference between distinct groups like Europeans, sub-Saharan Africans, and Australian Aborigines is something like 70,000 years of divergent evolution with very very minimal gene flow between the groups, in completely different environments. The genetic split between timber wolves and Chihuahuas was like 5,000 years ago and I bet they have common ancestors much more recently than that.
Well, for a start, this is completely wrong. Dogs diverged from wolves 20-40,000 years ago (lots of ambiguity over where exactly the divergence should be called), but from a now-extinct wolf species. While dogs and wolves _can_ interbreed, it doesn't happen naturally all that often (and when it does, it's pretty much all unidirectional; dog to wolf). Humans don't have the same issue.
A chihuahua, of course, is a result of deliberate and extreme forced breeding of a sort that (thankfully) has not really been practiced on humans. The closest parallel might be certain European royal families who had severe genetic diseases and abnormal physiology due to repeated inbreeding, but those were much, much less extreme. Dogs, though, were subject to fairly dramatic artificial selection from the start.
Any citation?
https://en.wikipedia.org/wiki/Early_human_migrations#Homo_sa...
Europeans have pretty low levels of sub-saharan genetic markers, with some remnant markets in southern Europe dating to the late Roman era, diminishing substantially as you move north.
Given how humanity has evolved, "european" markers are a subset of the diversity found in subsaharan populations that are overrepresented from founder effects, with very few exceptions. 40,000 years ago sounds like a long time, but it really isn't.
You need an amazingly small amount of migration (about one person per generation) to keep a population in sync with each other genetically.
>You need an amazingly small amount of migration (about one person per generation) to keep a population in sync with each other genetically.
Well it depends on the size of the population, but even then I don't see how this can be the case. One individual only contributes half their genes to each child, so assuming 2 surviving children that's a 25% lost immediately in the next generation. In just a few generations about half the incomer's genes will be lost in this way. The remainder will likely persist, but equally the number of their descendants that have none or very few of their genes will rise to predominate. In a stable population of 1,000 people, one single individual is unlikely to contribute much more than 1/2,000th of the genes in circulation.
It also means that a modern Japanese person has thousands of "Japanese" ancestors from whom they received zero genes. Of course, this is a bit of misdirection, as the genes that one receives are not unique, but drawn from a pool of possible genotypes common to humanity. The matter of how closely we resemble each other is not one purely of ancestry, but of the size of that pool - our overall genetic similarity. From what I gather, it's not an exceptionally large pool. I may not have gotten whatever gene controls the formation of the human prefrontal cortex from the same nth ancestor as you, but I got it all the same.
Also, where does dominance play into this, I wonder?
This really seems to have some huge assumptions in there. What is commonly understood? I don't think there is much common understanding associated with this. Except maybe that we should treat individuals as individuals, rather than make strong distinctions based on group membership, regardless of any underlying distinctions in the groups. At least that's the noble intent -- I don't think any lies are layered on this.
> When DNA recombines at conception, it only snips and stitches in a fairly limited number of places. It doesn't 'mix' finely like paint.
I had always assumed that clearly recognizable traits that children inherit from parents are simply based on the large influence of certain small pieces of DNA. Do you know a good text that discusses that?
I never understood this position from the logical point of view.
Say that you were put in front of two pictures that are entirely covered except for a small visible part each. The two visible parts of the pictures are different. Would you ever assume the parts that you can't see to be identical, or would you assume they differ from each other as much as the visible parts do?
Some very small genes have very large visible expression. Some large chunks of DNA have very little.
Let me change your italics:
Some very small genes have very large visible expression
So small parts of the DNA code for changes that we can visually appreciate. This doesn't mean that the rest of the DNA contains no variations, but just that we cannot see them. But it would be wrong to assume that the only parts that are actually different are those which encode for visible characteristics.
This seems like a clearly recognizable inherited trait, based on a large influence of certain small pieces of DNA. The abstract mentions eye color as well.
All living people share exactly the same set of ancestors from this point back, all the way to the very first single-celled organism. However, people will vary widely in how much ancestry and genes they inherit from each ancestor, which will cause them to have very different genotypes and phenotypes.
This is illustrated in the 2003 simulation as follows: Considering the ancestral populations alive at 5000 BC, close to the ACA point, a modern day Japanese person will get 88.4% of his ancestry from Japan, and most of the remainder from China or Korea, with only 0.00049% traced to Norway; conversely, a modern-day Norwegian will get over 92% of his ancestry from Norway (or over 96% from Scandinavia) and only 0.00044% from Japan. Thus, even though the Norwegian and Japanese person share the same set of ancestors, these ancestors appear in their family tree in dramatically different proportions.
A Japanese person in 5000 BC with present-day descendants will likely appear trillions of times in a modern day Japanese person's family tree, but might appear only one time in a Norwegian person's family tree. A 5000 BC Norwegian person will similarly appear far more times in a typical Norwegian person's family tree than he will appear in a Japanese person's family tree.
https://en.wikipedia.org/wiki/Identical_ancestors_point