The Two People We’re All Related To
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The Two People We’re All Related To

You have the materials inside you, right now,
to unlock the story of your deep, distant ancestry. And also mine. That’s partly because you have mitochondria
in your cells. And you got them only from your mother, not
your father. And if, on your 23rd pair of chromosomes,
you have an X and Y, like I do, rather than an X and an X, then you got that Y chromosome
only from your father. Together, these two facts mean that there’s
an unbroken line of mothers and mothers’ mothers who passed down the DNA in their mitochondria
for hundreds of millennia, creating a biological thread that connects you to a single female
ancestor, regardless of your gender. And it also means that there’s a lineage
of fathers and father’s fathers who passed on their Y chromosome, uninterrupted, leading
back to a single male ancestor. Now, I know what this might sound like. I’m not talking about the first two people. I’m talking about two humans who lived at
different times in the distant past — about 200,000 to 300,000 years ago. I’m talking about two people who never met,
but who, because of this odd quirk of genetics, combined with some unique evolutionary circumstances,
managed to pass on a very small fraction of their genomes to you. And to me. To all of us. And this is an incredibly powerful tool for
studying where we all came from. We’re only beginning to understand the legacy
of these two people to whom we’re all related — a legacy that goes back some ten thousand
generations. Let’s talk about where this legacy begins,
in your own cells. Your mitochondria are the small structures
that produce energy for your cells. And they’re relics from the time, more than
two billion years ago, when our ancestor was single-celled. And at some point, it engulfed another single-celled
organism and started using it as an energy supply. As a result, mitochondria today still have
their own, if very short, genomes. This is your mitochondrial DNA, or mtDNA. And it’s only passed down from the mother,
because egg cells have lots of mitochondria, but sperm cells only have a little, and they’re
destroyed after fertilization. Meanwhile, the Y chromosome is the smaller
of the two sex chromosomes, X and Y. People with an X and a Y, instead of two X’s,
are physiologically male. And there’s a reason we study mitochondrial
genomes and Y chromosomes to understand our ancestry. Actually, two reasons. Because they have two important things in
common: Their genomes are both pretty short, and they
also don’t recombine. Here’s what that means: In the process of
creating sperm and egg cells, our chromosomes line up and exchange information. Matched pairs of chromosomes swap arms or
legs with each other. This molecular do-si-do is known as recombination,
and it means that offspring will have a slightly different combination of genes on each of
its chromosomes than its parents had. This is basically how sex creates new genetic
variations. But Y chromosomes are much smaller than X’s. And unlike the rest of our chromosomes, it
doesn’t match its partner. So it doesn’t recombine with the X. And the mitochondrial genome doesn’t recombine
with anything either. Because it doesn’t have a partner to combine
with. All of this means that these two snippets
of genetic information get passed on, almost unchanged, from parent to offspring. Which makes them traceable through time. So for decades, scientists have been studying
these two bits of information. And they tell two stories about our history
that are slightly different but still complement each other. For example, one of the most important things
we’ve learned about ourselves from mitochondrial DNA is the story of human migration. Even though it’s passed on from mother to
child without recombining, mtDNA does slowly accumulate mutations. And as those mutations get passed on within
a population, they start to form a genetic pattern within that group. This allows scientists to organize us into
genetically similar groups, called haplogroups. Anyone who’s used a DNA test kit has heard
of these. So if you and another person share most of
these mitochondrial mutations, then you belong to the same haplogroup. And, decades of research into mtDNA has shown
that the vast majority of haplogroup diversity exists inside Africa. For example, there are several haplogroups
that are only found in Africa, or among people of African descent. These are groups like L0, L1, L2, and L4,
5, and 6. But! The whole rest of the world is represented
by parts of only one haplogroup! That’s L3. So if you’re of non-African descent, you
belong to L3, which contains lots of subgroups, like K, M, N, and R, which are found among
populations outside Africa. But there are even more subgroups of L3 found
within Africa. So what does all of this tell us? Well, for one thing, it’s taken as genetic
evidence for what’s known as the “out of Africa” hypothesis — the hypothesis
that modern humans originated in Africa, and spread throughout the world. This model was first developed by anthropologists
around the 1980s, based on skeletal evidence — specifically, the earliest anatomically
modern humans that were found in southern and eastern Africa. And today this mitochondrial data is seen
as molecular support for that idea, starting with a famous paper published in the journal Nature in
1987. That paper detected the first signs of these
genetic patterns, based on mtDNA sampled from just 147 people from five different geographic
populations. But among other things, that study showed
us that there’s such a great diversity of haplogroups in Africa, because that’s where
our genetic populations are oldest. So when a small group of people migrated out
of Africa, they only represented some of the genes in the total human gene pool. Those migrants became the founders of their
own genetic lineages, found within the haplogroup L3. But there was still an older, source population
in Africa that they used to be a part of. Now, we can also use changes to our mitochondrial
DNA to estimate when certain lineages split off from each other. This method is known as the molecular clock,
which we’ve mentioned before. It’s based on the idea that mutations occur
in mtDNA at a pretty regular rate. But since that rate of change isn’t the
same across all of humanity, the clock needs to be calibrated, like with the help of well-dated
fossils and even the DNA of ancient fossil humans. Using this method, scientists have traced
the mutations in all of the major lineages of people from haplogroup L3 that appear outside
of Africa. Where those non-African groups converge in
time, we find the earliest humans that left Africa. And the data suggest that this happened around
70,000 years ago. And going back even further, it appears that
all known haplogroups converge at a single female ancestor who lived roughly 200,000
years ago. So our mitochondrial ancestor can tell us
a great deal about where we came from, and when. But we also have to talk about what she can’t
tell us. She isn’t the first woman of our species,
or the first anatomically modern human, or anyone really special, for that matter. For one thing, there’s evidence of modern
humans as far back as 300,000 years ago in northern Africa. So we know our species was around long before
this woman lived, for thousands of generations. But their mtDNA just didn’t make it to the
present day. The fact that the one woman passed on her
mitochondrial genome to all of us is really just a matter of chance. Think of it this way: In any given generation,
a woman might have sons but not daughters. And if she only has sons, that means none
of her mitochondrial DNA will get passed on. So our mitochondrial ancestor is the only
person who managed to have one or more female offspring, who in turn also had female offspring,
in an unbroken line, for the past 200,000 years, by sheer chance. Now, naturally, there are lots of limitations
to what mtdna can tell us. The dates they provide us aren’t very precise. And the genomes themselves are small, representing
a tiny fraction of the information that’s in our whole genome. And, of course, they only tell us about half
the population: females! So while mtDNA was crucial as an early source
of genetic data, as sequencing methods started to improve, scientists began studying the
other non-recombining stretch of DNA: the Y chromosome. Much of this work was done in the early 2000s. And, just as mtDNA can shed light on the growth
and spread of certain maternal bloodlines, the Y chromosome can tell us about the migration
patterns of some groups of men. For example, a pair of studies in 2010 and
2013 sequenced both Y chromosomes and mtDNA from 2,740 people across Indonesia. And the results showed that a surprising amount
of Y chromosome DNA came from far away — like China, India, Arabia, and even Europe — especially
in Indonesia’s western islands. On the island of Borneo, for instance, the
presence of the Y haplogroup known as O-M7 seems to be the fingerprint of immigration
of men from Han Dynasty China, about 2,000 years ago. But! In those same men, their mitochondrial DNA
more closely resembled local haplogroups. So that suggests that, at least over the past
few thousand years, men had been arriving from elsewhere and pairing up with local women. And, when it comes to how far back this Y
chromosome goes, the latest molecular clock calibrations now suggest that our Y chromosomal
ancestor lived from about 200,000 to 300,000 years ago. Much like with our mitochondrial ancestor,
this guy must have had at least one male offspring, who in turn had more males, in an unbroken
line for hundreds of millennia. Now, we don’t really understand why these
two individuals left the indelible mark that they have on our genomes. One idea is that there might’ve been a boom
in the human population around 200,000 years ago in Africa, when our species happened to
be doing very well for itself. If that were the case, then the offspring
of both of those people may just have been more likely to survive, and pass on their
DNA. Or, in the case of our Y ancestor, it could
be that he had a sorta Genghis Khan thing going on, having many many many kids, some
of whom were sons who also went on to have many many many kids. But the story that these two people can tell
us ends when they were born, because we can’t trace their genetic trail any further back
in time. So, to probe the origins of anatomically modern
humans, we need earlier sources of data. Remember: The Y chromosome and the mitochondrial
genome represent just a small fragment of the human genome. To understand the whole range of human diversity,
we need to study…the whole range of human diversity. Luckily, this is the 21st century, and we
no longer have to sequence tiny stretches of individual genomes by hand. We can sequence whole genomes, and quickly. So as our technology and methods improve,
we may soon be able to reach beyond the lives of these two ancestors, into the even deeper
past. But even when we do, each of us will continue
to carry the molecular legacy of one man and one woman, who managed to make their mark
on all of humanity. Thanks for joining me today for this truly amazing story. And BIG thanks to our Eontologists: Jake Hart,
Jon Ivy and mah boi STEVE! Now, Lemme give you my two cents. Actually, “Two Cents” is a new series
from PBS Digital Studios about money and YOU. Financial experts (and husband and wife team)
Philip Olson and Julia-Lorenz Olson guide you through the complex world of personal
finance, from the kitchen table to the Stock Exchange. You’ll get practical knowledge about how
to spend, save and earn, and even insights into how your brain is hardwired to react
to economic problems. Money might make the world go round, but it
doesn’t have to make your head spin. So check the link in the description below
to subscribe to “Two Cents”! Now, what do you want to learn about? Leave me a comment, and don’t forget to
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100 thoughts on “The Two People We’re All Related To

  1. Amazing informations but this one is a little confusing. I love these little shows. I'm trying to watch all of them! Thank you to everyone who makes these possible!!

  2. Mutation Question: Although mutation rate is constant, the ability to pass on the mutation, dependent on internal and external pressures, cannot be constant.

    An internal pressure can make the new mutant offspring be in capable of surviving the gestation or have the ability to mate, like mechanically. An external pressure can make a new mutant offspring, like an albino, not be able to hid from predators.

    And even if an offspring was able to mate, the number of offsprings may be too little to be capable of a continual passing down of the new mutant gene. And thus like an albino offspring, this mutant gene is not able to establish a foothold to snowball forth in our biological and geological time.

    So a new mutation may have had to occur numerous times before it is capable of making it stick. For nothing in life happens the first time and then every other time have the success rate of 100%, not even new mutation.

    And a new mutation may not be generalizable to behave the same as all mutations, the fruit fly’s eye color or Mendell’s plant.

    Eventually all genes must be able to be passed on consistently for all of us to have similar genes to all things; however, my focus in to not water down the grave difficulties a new mutation must have faced, and perhaps numerous times, before it is able to establish a foothold of the runaway train.

    Perhaps make a video on this Eon. Thank you.

  3. Wait, didn't super dad have a dad, who must have had the same y chromosome, and super mom had a mom. How does this line ever get concluded?
    😐 I might actually be an idiot. I just can't visualise this information. Any other confused cousins? 😕

  4. Hold on
    Does this mean all females are related to each other and all men to each other but not women related to men? I'd think it would work like that. I don't see how any woman would be related to that man or men in general I guess if the y chromosome only gets passed to males and mitochondrial DNA to females.

  5. thats kind of beautiful – all of our's mom lived in africa ten thousand generations ago and managed through her daughters to spread mtdna through all of the world…talk about that – the time when all man was one

  6. If My understand ing is correct about mitochondria and evolution, is it posible that the DNA in question is not necessary Human? Correct me if im wrong, is there a posibility that the owner of the genome in question might be a Pre Homo sapien Species?

  7. Due to interspecies fertility, those two "people" do not have to belong to our own species, nor to our subfamily (homininae) and might be much much older than the few hundred thousand years quoted in this video.

  8. Hey cousins who want him to speak slower, click on the three vertical dots at the right hand corner and change the playback speed to .75

  9. Actually, a few genes on the Y do have peer alleles on the X, and they do re-combine with them. Most of the Y does not, and that’s probably good enough for this method.

  10. Now that we’re all related let’s stop getting married and having sex or doing any type of that love thing because that’s ices

  11. Imbeciles, you are assuming that life began with 2 pairs and not a myriad of cells in a cesspool of ?. If everything that you said is true, scientists would be able to produce life in labs without sex. Go back to middle school PBS.

  12. We don't actually know for sure they never met. They don't HAVE to have met, they PROBABLY never met, but it's just about POSSIBLE they met.

  13. Please tell me I’m not the only one who immediately went ‘is the power house of the cell’ after he said mitochondria?

  14. One thing not emphasized in this: Taking about the woman (the man is similar), she lived in a village just like everyone else in her time – she had ancestors herself. There is no special difference between her and the others living there, and those others are also our ancestors – just not through an exclusively female line. The only thing we know about her for sure is that she had at least two daughters who went on to have families and descendents down to the present time. And yes, her mother's line were also mothers of all alive today, but she is distinct because she was the latest one.

  15. What about negative blood people. So look into this as negative blood women can not breed with positive blood males. Found initially in Europeans

  16. Hear that all of you racist, sexist, elitist out there!! We are all related so you are no better than me and vice versa.

  17. We are all brothers and sisters. Not literally, but. We should treat one another in such a compassionate way. This episode has me pause and exclaim, "What????" when I heard about how far back these two people go. Truly amazing and awesome.

  18. @PBS Eon: Heyyyy. Shouldn’t we update this video now since we recently found out mtDNA can also now be inherited by fathers?

  19. i hope he understands that you can get an x chromosome from your father too. he only mentions getting y chromosomes from the father.

  20. My maternal line came to Finland trough Western Europe from Central Asia. My paternal line came to Finland from South East Asia trough Siberia. I am a typical Finn.

  21. wait wait wait…. Males are male because of the Y chromosone, and yet there were males… without the y…. im so confused…… And I thought mitochondrea was like vital for our bodies to make energy??? how did humans live without them?? IM SO CONFUSED

  22. the pseudosomatic part of chromosome Y does recombine… Its funny how quick things change! this video is from oct 2018. In nature (Jan 2019) this is somewhat contradicted, saying that fathers also occasionally contribute, not just mothers.

  23. I'm impressed that no one brought up the whole racism mental disorder. Were all related? More than once…probably 2 or 3 times throughout human history. Q the banjo

  24. This makes me think about those Conspiracy Theories that say all U.S Presidents are related. It goes to show you most of us are related to those fools too.

  25. These are great videos (discovered this channel yesterday) but this one has been the biggest WOW for me😮

  26. We are not of this world. In fact we are out of this world. Every other living thing on this planet moves in such synchronization with each other. From weather, to mating, to hibernation, to hunting and eating, everything is in tune with this planet. The only thing that is not is us humans. Even if your a vegan who recycles, who is a member of green peace and is living as green as one can be, if you are walking on paved roads and sidewalks then you are still part of this planets problem. We are the only thing that disrupts the balance of this planet and maybe it's cause we are not of this planet. Maybe our origins are more in tuned with another planets solar cycle. Cause on this planet no matter how aware we are and how careful we are trying to live we are still disrupting the eco system that is not our own.

  27. Can you explain why North American indigenous people have teeth only found in Mongols?
    Is it possible there was a reverse migration from NA to Asia?

  28. By the time they figure out the DNA 🧬 & other human identifiers of our first male & female ancestors the human species will succumb to the effects of climate change.
    Humans need the earth, the Earth doesn’t need humans.

  29. The "we don't understand why" part is like saying you don't understand how a coin ever lands on heads. This "last common ancestor" via either method will always have a result unless you evolved separately (in which case it's almost impossible you could interbreed). Furthermore, as long as populations aren't genetically separated, it will happen again and again. As genetic lineages continue to die out, the last common ancestor will leap forward each time an ancient separate population dead ends. The newer last common ancestor will of course be a descendant of the previous last common ancestor, the only thing changing is who is most recent and fits the criteria.

  30. The Garden of Eden was by the Euphrates and the Tigris rivers. That puts it in Iraq. People from there migrated to Africa and other places. So we all didn’t come out of Africa.

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