[Music]
about eleven and a half thousand years
ago people in what's now central Alaska
buried two babies in a hearth one was
less than six weeks old and the other
was a late-term stillbirth they stayed
there until 2013 when archaeologists
found the remains and this week a group
of researchers published a detailed
analysis of one of the babies genomes
it's full genetic code in the journal
Nature turns out that this one baby's
DNA can tell us a lot about our history
as a species it's the most direct
evidence we have for how people first
came to the Americas and what happened
to them afterward over the years
researchers have proposed lots of
different theories for how the first
Americans got here and these days there
are at least a few things that almost
everyone agrees on at some point
probably more than 14,000 years ago
people crossed over the bering land
bridge between what are now Siberia and
Alaska from there they spread through
north and south america splitting off
into northern native american and
southern native american genetic groups
which are still around today there are
plenty of unresolved questions about
this though like when exactly the
migration happened and why the ancient
Native American and East Asian genomes
are so different enter the babies from
this week's paper the researchers were
only able to isolate enough DNA for a
full genome analysis from the six week
old baby known as US r1 they sequenced
us our once genome and compared it to
both ancient and modern genomes for more
than 2,500 people they found that us r1
wasn't nearly as closely related to the
northern and southern Native American
groups as you might think it's clear
they had a common ancestor but according
to the team the babies genetic code was
so different that it's part of a whole
separate lineage a third group that
they're calling the ancient Beringia
pnes that supports what's known as the
Brin G and standstill model which
suggests that people first came to the
areas near the land bridge aka Beringia
something like thirty thousand years ago
but then the ice age peaked and the ice
sheets and glaciers made travel so
difficult that the people in Beringia
were basically cut off from the rest of
the world for thousands of years hence
the stand still part of the name
according to the model once the climate
warmed up a little people weren't
trapped anymore
and they started to move out into the
rest of North and South America if the
first Americans were stuck in Beringia
for a while breeding amongst themselves
and developing new mutations in their
DNA these changes wouldn't be
shared with the East Asian population
they came from so you'd expect there to
be a lot of diversity in the ancient
Native American genome and the ancient
brynne gene lineage tells us there was
the findings also fit what researchers
found back in 2015 when they looked at
the babies mitochondrial DNA that's the
separate smaller genetic code in a
cell's mitochondria as opposed to the
nucleus they were able to get good
samples from both us are one and the
other infant us are two even though the
mitochondrial genome doesn't have as
much information as the nuclear genome
it's still a useful tool and it was
enough to show that the two babies were
each part of genetic lines you don't
generally find in today's northern
Native American populations in other
words it showed that the babies must
have come from a pretty diverse
population and now that we have us are
ones nuclear genome we know that there's
more to it than that
the ancient Varangians were a whole
separate group and by comparing us our
one's genome to those of other groups
the researchers were also able to flush
out the Bur in G and stand still model
and come up with a much more solid
timeline of when and how the first
Americans moved in to be clear we don't
know for sure that this is exactly how
it went but by combining this new
evidence with what archaeologists have
found in the past here's what the team
thinks happened people first settled in
the area of Northeast Asia near the land
bridge around 36 thousand years ago but
for a while after that there were still
people going back and forth to the rest
of East Asia and genes being shared
between the populations then about
24,000 years ago the cooling climate
isolated them from each other around
21,000 years ago us our ones ancestors
and the ancestors of both the northern
and southern Native American groups
split into two separate genetic lines
it's not clear whether they cross over
the land bridge before or after the
split but either way they still couldn't
get very far because of all the ice then
sometime around fifteen thousand seven
hundred years ago the northern and
southern Native American groups split
off from each other and this was right
about when the climate finally warmed up
a bit and people started to move farther
east eventually spreading throughout the
Americas about four thousand years later
two babies were born and died in Eastern
Beringia and now 11,500 years after that
their remains have brought us the
closest we've ever been to understanding
how the indigenous peoples and cultures
in the western half of the planet came
to be thanks for watching this episode
of scishow news and a special thanks to
our president of space SR Foxley
thanks SR also if you like this video
you might like our sister channel PBS
Aeons which is all about the history of
on earth including some very weird times
like when whales walked or when oxygen
almost killed everything if you want to
check it out just go to youtube.com
slash Aeons
[Music]
you
[Music]