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