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think for a moment about every single
person you've ever met in your life then
think about everybody you've ever heard
of and finally think about everybody
alive on the planet right now no matter
how far away or close all of these
people may seem including me talking to
you right now through this video all of
us are related to you and all of you are
related to me so how can this be using
some very simple math we can take a
glance at your family tree you obviously
had two parents and your parents each
had two parents of their own which means
you have four grandparents you have
eight great-grandparents and this number
doubles each generation you go back just
five generations ago or 125 years before
the date you were born you theoretically
would have had 32 ancestors living on
earth at that time however going back a
thousand years before you were born or
forty generations ago you would find
with this math that you would have over
a trillion ancestors living in the
Middle Ages which is more people than
have ever existed in all of time
combined obviously there's a variable we
haven't accounted for in these
calculations yet and that variable is
incest a lot of it for most of human
history the only people somebody may
ever really meet were the people in
their local village town or tribe this
obviously limited the dating pool to
just a handful of options and those
options often included people like
cousins not all of your ancestors are
unique to only you or your family if you
compare your family tree with your
friends tree and you go back far enough
you'll see the shape of the tree slowly
vanish and see something that resembles
more of a web as you draw your two webs
out you'll eventually find a common
ancestor between yourselves at some
point which would make you both
distantly related the further back in
time we go the more common ancestors all
of us end up having about 0.5% of the
modern human population can claim direct
ancestry from Genghis Khan
largely in the region of Asia between
China and Uzbekistan going even further
nearly anybody with European ancestry
can trace their origins to the same
group of ancestors roughly 1,000 years
ago
this means that statistically if you
have European ancestry anybody living in
Europe around the ninth century who had
children and grandchildren is one of
your direct ancestors meaning that since
Charlemagne had 18 kids he's most likely
somewhere in your family web but who is
the most recent person that all of us
alive on earth watching this video can
mutually trace all of our ancestors back
to this person is known as the most
recent common ancestor or MRCA
and he or she is believed to have
existed not terribly long ago they may
have existed as recently as just 300 BCE
just after the conquests of Alexander
the Great and they almost certainly
lived somewhere in East Asia in either
come Chaka Japan Taiwan or Indonesia
this person had amazing reproductive
success and was likely a merchant that
traveled extensively with their
offspring venturing off and creating
their own offspring over time in the
far-flung parts of the world like the
Americas and Australia this single human
who lived there in this time is the
direct ancestor of every single person
alive today which links all of us
together in the giant family web that we
call humanity but it doesn't mean that
MRCA was the first person to have
children nor does it mean that nobody
else alive then has direct descendants
today there are many MRCA
is simply the first person in world
history who can count universal
descendants today but many of our
ancestors live significantly further in
the past than they a nine thousand year
old skeleton dubbed cheddar man was
discovered in a cave near the English
city of cheddar back in 1903 recent DNA
analysis of the remains revealed
something astonishing 9,000 years and
300 generations later cheddar man has a
direct descendant living today and he
only lives half a mile away from the
side of the cave and teaches history if
you rewind the clock even further back
it's possible that 70,000 years ago the
entire global population of humans may
have shrunk to as little as 10,000
people that's only a ninth of the
seating capacity at Wembley Stadium and
then when you consider those few people
were spread out across Africa and
Eurasia you remember what I said earlier
most people only ever dated people who
lived nearby because they literally had
no other options we all share multiple
common ancestors that all of us can
claim to be descended from it's just
that that person in 300 BC II is the
most recent one that all of us can claim
if you think about it in terms like this
if you fail to have children you're the
first person in an unbroken chain going
back hundreds of thousands of years to
fail to do so in fact it's even more
serious than that when you consider the
most recent common ancestor of all
living things
today this organism is known as the last
Universal common ancestor or Luca for
short Luca is believed to have existed
3.5 to 3.8 billion years ago and
everything that's alive on earth right
now from you and me to bananas that
annoying mosquito Greg and the bacteria
on your face are all direct descendants
of it when you think like that if you
fail to reproduce during your life
you're the first organism in an unbroken
chain going back over three billion
years to fail and that may make your
ancient ancestor Luca rather sad but
what's interesting about all of this is
that if you go back far enough not only
is all of humanity one giant
interconnected family but all of life
itself on earth is just one
incomprehensible huge interconnected
family so the next time you stomp on
that bug or SWAT that mosquito remember
that you both are technically part of
the same big family the origins of
humanity and life itself are as
mysterious as they are interesting but
they're still
prising amount that we actually know
using math we can calculate certain
things like where your ancestors
probably originated from and we can come
up with theories like who all of us are
directly descended from the scientists
that work to figure all of these things
out are like detectives investigating
thousand year old crime scenes that
literally impact all of us today and the
computational biology course at
brilliant will explain to you how all of
it works and why it affects you
personally the course has an entire
section dedicated to human ancestry that
this video was heavily influenced by
brilliant as I'm sure you know by now is
the best place to learn about complex
topics because they teach you the
intuitive ideas behind them so you
understand how it all works together
rather than just memorizing phrases if
you want to become the kind of person
who can explain where your ancestors
came from going back thousands of years
based on your own genetic evidence then
brilliant is the right place for you as
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