Proof of what?
Everybody alive descends, in the female line, from one woman who lived in Africa about two hundred thousand years ago. Every man alive descends, in the male line, from one man of about the same period. She is called mitochondrial Eve and he is called Y-chromosomal Adam.
Both findings are real. Both are quoted as proof that our species began in Africa.
Neither shows that. What produces a single ancestor in those two lines is arithmetic that operates in any population anywhere, and it says nothing about where that population started.
What was actually measured
The two dates do not sit together. Hers is usually given as a hundred and fifty to two hundred thousand years ago. His has moved between sixty thousand and three hundred thousand across different studies, and the current figure is around two hundred thousand.
So they lived tens of thousands of years apart, which already rules out a founding couple.
And there were many thousands of other people alive alongside each of them. Those people are your ancestors too, through lines that are not the female-only line and not the male-only line.
What was found is not a first man and a first woman. It is the point at which two particular chains converge.
Your tree folds
Count your ancestors backward and the number doubles every generation. Two parents, four grandparents, eight great-grandparents.
Thirty generations back, which is around seven hundred and fifty years, the arithmetic gives you a billion ancestors. The world at that time held about four hundred million people.
So the tree cannot be what the arithmetic says. It folds back on itself, and the same people appear in it many times over, in different places, because your ancestors were marrying each other's relatives the whole way down.
Geneticists call this pedigree collapse.
Which is all Eve and Adam are
Take that folded tree and follow one edge of it.
Go mother to mother to mother, never once through a father. That is a single chain and it reaches one woman at any depth you choose.
Go father to father to father, never once through a mother. Another single chain, another single man.
Every other ancestor is reached by some mixed path, and the mixed paths are almost all of them. Only the two outer edges are single.
Everyone alive is on one folded tree, because the population that produced us was small and intermarrying for hundreds of thousands of years. So everyone's female edge runs back into the same pool, and everyone's male edge does too, and far enough back each arrives at one person.
That is mitochondrial Eve and Y-chromosomal Adam. Two edges of a tree that everybody shares.
And it proves nothing about origins. It does not mean humanity began with two people. At every point in the past there were hundreds or thousands of common ancestors, and Eve and Adam were two of them. The others are in your tree as well, through every path except the two outer ones.
What the finding shows is that if you look far enough back, we are related to everybody who was there. If the founding group three hundred thousand years ago numbered a few thousand, then every one of them who left children at all is an ancestor of every person now living.
How small the population was
The numbers can be read out of living DNA. Variation accumulates at a known rate, so the amount of it in a population tells you how many people were breeding, and when.
The figure that comes out for most of our existence is small. An effective breeding population of around ten thousand, holding roughly flat for hundreds of thousands of years.
Effective population means the number actually contributing to the next generation, which is always smaller than the headcount. Ten thousand effective might be thirty or forty thousand people alive.
And the line does not hold flat the whole way. It narrows.
A very deep one is placed around nine hundred thousand years ago, on one analysis, taking the breeding population down to something like a thousand for over a hundred thousand years. That finding is disputed.
Another sits around seventy thousand years ago, at the time of the Toba eruption, which some work puts at a few thousand breeding individuals.
And the male line collapses on its own between seven and five thousand years ago, roughly twentyfold, with the female line untouched.
So the shape is a long thin thread with knots in it. Never large, occasionally very small, and small enough for long enough that everyone in it ends up in everyone's tree.
What narrowed it
All of the above is mainstream genetics, and mainstream genetics attributes the knots to climate, disease and volcanoes.
On the esoteric account something else was operating alongside those.
The interventions did not stop at the making of us. Different alien races worked with different populations, and what they produced were peoples built to expand: better organised, better at war, and better at holding what they took.
And the work was not only genetic. A people was given a culture as well, usually a religion, and the culture did what the genetics could not. It bound strangers into one body, supplied a reason to fight, and made an empire possible where there had been tribes.
The result is a population that spreads over its neighbours and replaces them.
That process is visible in the record and it is visible through the male line, because the men move and the women are taken. Genghis Khan is the case everyone knows: something like one man in two hundred across a wide belt of Asia carries his Y chromosome. Alexander did the same thing at a smaller scale, and so did the Arab expansion, and so did the Bantu, and so did the Indo-Europeans before any of them.
Each wave narrows the thread. A great many lineages end and one spreads across the ground they held.
And each wave simplifies. What was many peoples with many languages and many gods becomes one people with one language and one god, which is easier to organise and easier to command.
So the bottlenecks in the mainstream account are climate and catastrophe. On this account a good many of them are us, expanding under direction, and the direction came from outside the planet.
Why one line wins, with nobody choosing it
This is the part that sounds wrong and is arithmetic.
Mitochondria pass from mother to child, and only daughters pass them on. A woman with only sons passes hers to nobody. Her line ends there.
Now the key point. A mitochondrial line can never split into two different lines. All of a woman's daughters carry what she carried. So the number of distinct lines in a population can go down, when a line runs out of daughters, and it can never go up.
Anything that only decreases, and never increases, arrives at one. There is nowhere else for it to end.
No selection. No advantage. No shrinking population. Lines end, none are created, and eventually one is left standing.
How long it takes
Start with a thousand women, each with a different line.
Each generation, some have no daughters. Those lines end. On average the number of distinct lines halves every few hundred generations.
A thousand becomes five hundred. Five hundred becomes two hundred and fifty. Ten steps of halving and a thousand is one.
For a population of ten thousand women it takes something on the order of twenty thousand generations. At twenty years a generation that is around four hundred thousand years.
Which is the right order for the dates we have.
A case from ordinary life
Family names do the same thing, in the countries where a wife takes her husband's name.
A family with only daughters loses its surname in one generation. Nobody decided anything. There was no son to carry it.
Run a closed village for a thousand years and most of the original surnames are gone. Run it long enough and one is left. Everyone in the village shares it.
And they are still descended from all the original families, through their daughters. Only the label disappeared.
Iceland and rural Japan both show this on a small scale, and so does any long-isolated village.
The one difference, and it is the reason surnames never quite get there. New surnames are invented. People change them, immigrants arrive with different ones, new families appear. That constant injection keeps the count up.
Mitochondria have no injection. Nobody arrives in a species carrying a mitochondrial line from outside it. Mutation changes a line slightly without making it a separate lineage.
That is the whole difference, and it is what forces the count to one.
Why the rest of your DNA does not do this
Your ordinary chromosomes are cut up and mixed with your partner's every generation.
So a chromosome does not descend from one person. A single chromosome in you is a patchwork from thousands of ancestors, and there is no line to follow and no line to run out.
Trace different pieces of your genome back and they converge on different ancestors at different dates. Some over a million years ago. The nuclear genome has no single point of origin at all.
Mitochondria and the Y are the two pieces that never shuffle. They pass whole, unmixed, from one parent only.
That is the only reason they have single-point ancestors, and it is why those two dates get quoted while the rest of the genome is left out of the story.
And mutation does not blur it
Mitochondria mutate constantly. Every line accumulates changes, generation after generation, which is why no two people carry exactly the same sequence.
That looks as though it should destroy the picture. It does the opposite.
A mutation adds a mark and it does not erase the marks already there. So a line carries everything that ever happened to it, in order. The oldest changes are shared by everybody descended from the woman they occurred in. The newest are shared by a handful of cousins.
Which means the accumulated mutations are a record rather than noise. Sort people by which changes they share and the tree assembles itself, with the deepest shared marks at the root.
And the rate is what supplies the date. Mutations arrive at a roughly steady pace, so counting the changes between two lines gives the time since they parted.
So mutation is not hiding the single ancestor. Mutation is how she was found.
A test. ACTION ITEM
A mitochondrial line can only be lost. Nothing inside a species can create a new one, which is why the count falls to one and stays there.
Unless a line arrives from outside the species.
If our ancestors were hybridized with an extraterrestrial mother, her mitochondria entered the population that way. Not as a variant of ours, but as a separate lineage with its own history behind it. An extraterrestrial father does the same for the Y chromosome.
That leaves a mark, and the mark is measurable.
The measure is divergence: the number of letters at which two lines differ. Mutations arrive at a roughly steady rate, so that number gives the time since the two parted, and the whole tree was built out of it.
Any two people alive today differ in a few dozen letters out of sixteen thousand. Trace it back and every line meets every other around two hundred thousand years ago.
A line that came from another world would not do that. It would differ in far more letters than any human pair, and the count would give a time of separation that nothing on this planet can account for.
Finding one would show that material entered our species from a source outside it, at a datable moment, from a donor whose own line can be measured.
Nobody is looking, and the reason is that a sequence which does not fit the tree already has three places to go. It gets filed as contamination, as sequencing error, or as a numt, which is a fragment of mitochondrial DNA that copied itself into the nuclear genome long ago and therefore looks ancient. Each of those is a bin for data that does not fit, and each is used constantly.
The action item. Search the public mitochondrial and Y databases for lineages with impossible divergence depths, and then go back through everything that was discarded into those three bins and look at it again.
The sequencing is done and the data is public. What is needed is the search, and the reason nobody has run it is that nobody has thought to.