B1 Intermediate US 8993 Folder Collection
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This is you.
And these are your ancestors, a huge pyramid stretching into the past and balancing right
on your head.
How many ancestors do you have?
Well, you have two parents.
Four grandparents.
And eight great-grandparents.
Four generations back, your direct ancestors total 30.
If we continue down this line, doubling every step, just 40 generations ago we’d find
a trillion ancestors, all living *at the same time*.
Which is… ridiculous.
That's not only more people than have ever been alive, it's more stars than are in
the Milky Way.
Since our species came on the scene 200,000 years ago, there have been maybe 7 or 8 *thousand*
generations of humans leading up to… you.
So where are all your missing ancestors?
Clearly, there’s been some inbreeding.
[OPEN]
We’re not talking banjo-playing, King-of-Spain, Cersei-Jaime inbreeding, but every family
tree inevitably grows forks.
Before Tinder, choices for mates were often limited to as far as you could walk.
Even people like Charles Darwin and Albert Einstein married their first cousins.
Because so many people with shared ancestors have reproduced, our number of actual ancestors
is much smaller than what simple math tells us.
If we replace that with fancy math, factoring in how people moved and lived and paired up…
life expectancy, trade, geography, Genghis Khan… we find something interesting: every
human alive today shares a common ancestor in their family tree, and this person lived
only around 3,000 years ago.
That’s right, next time you get in a fight with a stranger on the internet, just remember
that you share the same great great great great great (fast foward) great grandfather
or grandmother.
But we don’t know who that person was.
The math tells us they must have existed, but they didn’t leave fossils or artifacts.
Or like, a note or something.
Though, writing birthday cards for each of their 7.4 Billion great great great great
great (fast forward) great grandchildren would have been nice gesture.
But we all carry a record of our ancestors in our genes.
Because DNA is copied over and over, every so often a mistake is written in.
You know how when you make a copy of a copy, it’s doesn't come out as sharp?
Like that, but since most of our DNA can be changed without affecting how things work,
many of these mutations slip through to the next generation.
These genetic changes accumulate at a steady rate through time, so scientists can read
them like a molecular clock, and estimate how much time has passed.
And which changes individuals share tell us how closely or distantly related they are.
Humans *seem* really different, but on a DNA level we’re remarkably similar.
Groups of chimps in Central Africa, living right next to each other, show more genetic
variation than we find in the entire human population.
This genetic similarity tells us that our species is new, in the big scheme of things,
and that at one point our population was small, maybe as few as 10,000 of us.
To put that in perspective, that’s only a third of your average Bruce Springsteen
crowd.
Sorry Boss.
Today, any two humans only differ by about 1 out of 1000 DNA base pairs.
But our genome is so big, that’s still millions of single letter differences, or SNPs, for
“single nucleotide polymorphism”.
We tend to see combinations of these changes, chunks of SNPs, associated with different
geographic locations.
Companies that test your DNA ancestry read thousands of these single letter changes in
your genome, to make a sort of signature of your unique genetic variation.
Then they compare your signature to thousands of reference individuals from various parts
of the world, and do a bunch of fancy math to see which parts of your genome most likely
came from certain geographic areas.
My genetic results: Pretty much look like this.
My ancNewsprestors, on both sides of my family, are from Northern Europe and Scandinavia,
which explains my last name, why I’m tall, why I don’t tan, and also why I carry more
Neanderthal DNA than 2/3rds of people.
Confused why I have Neanderthal DNA?
You should watch our last video. I didn’t find any surprises, but many people learn
about ancestry they didn’t know they had.
Where we come from isn’t always obvious on the outside, but DNA doesn’t lie.
Before, using math, we identified an ancestor, not too long ago, that’s related to all
of us.
But that person’s genetic influence has been shuffled so much it’s invisible in
our DNA today.
Is there someone whose genes have been passed on, unbroken, to today?
Some leftover fingerprint from the mother of everyone alive?
There is.
You have a 47th chromosome.
It lives in mitochondria, the POWERHOUSE OF THE CELL! – so we’re doing that again?
Ok–mitochondria used to be free-swimming.
They have their own genetic material.
Unlike your other 46 chromosomes, there’s no shuffling when it’s passed between generations.
What’s more, all your mitochondria came from your mother’s egg, not your father’s
sperm.
They trace an unbroken line of ancestors stretching back through every female in your family tree.
By comparing the changes that have accumulated over the millennia, we find the most ancient
human mitochondrial DNA comes from Africa, where our species originated.
We can even trace it back to one woman, about 150,000 years ago.
Other Homo sapiens females lived alongside her, but only her lineage lives on today,
all other Homo sapiens lineages are extinct.
This is mitochondrial Eve.
And every single one of us, descend from her.
In the truest sense, we really are family.
Even if we’re just hundredth cousins or something.
But our ancestry isn’t just branches stretching into the past, it’s also a tree that extends
into the future.
Today we have more power to mold that future, down to the genetic level, than we’ve ever
had before.
So what might our species’ future look like?
Next time.
Stay curious.
This video is part of a special series we’re doing about the story of our species: Where
we came from, how we’re all connected, and where we’re going.
If you haven’t already, check out part 1 and 2 to trace the fossils in our family tree
and learn why we’re the only humans left.
And be sure to subscribe so you don’t miss any of our videos.
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Are We All Related?

8993 Folder Collection
韓澐 published on September 27, 2017    Ellen Hsiao translated    林恩立 reviewed
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