So what's the science we used to study
the ancient migratory paths of your
Ancestors?
It's something called population genetics, and it
helps us to piece together how humans
populated the earth.
Here's how it works.
Historically people close to each other
tended to share more of those genetic
markers – the little DNA typos passed on from
parents to their kids - then they did with
people on the other side of the world.
Makes sense, after all, who were they more
likely to meet fall in love with and have
babies with -
the people living nearby.
Over time, this created regional patterns
of genetic variation, so the people
living in, say, northern Spain
had more markers in common with each
other
than they did with people in Indonesia.
These regional patterns of variation
allow us to track the migratory paths of
your ancestors.
By looking at where in the world your
markers are found, we can figure out
where you came from
and by looking at the order in which
these markers have occurred over time
and where in the world they originated,
we can actually track the journey your
ancestors followed from an African
homeland
to where you came from more recently.
How do we find these markers in the
billions of a's g's c's and t's?
It's not easy.
It's a little like finding needles in a
haystack.
That's because when a mom and a dad
have had a baby, their chromosomes are
copied and passed on to their child, but
not in a straightforward way.
Instead, mom and dad's chromosomes are
shuffled when they are passed on to their
kids.
Imagine a deck of cards containing only
Hearts,
and another
containing only spades.
Now shuffle them up
and look at your hand.
It's going to be a mix of hearts and spades - 
the cards your parents have
but in a different combination.
This makes tracking our markers really
hard for most of our chromosomes,
but we found a shortcut.
There's one of your twenty three pairs
of chromosomes that gets passed on
virtually unchanged it's called the
Y Chromosome.
If we look at your Y chromosome, the
markers that your ancestors left you from
thousands of years ago should still be
in the same order.
But there's a catch to the Y
Chromosome, it exists only in males
passed on directly from father to son.
In fact, it's the Y chromosome that
makes the male a male.
There's another kind of DNA
located in a different part of the cells
it's only passed on from the mothers to
Children, 
it's called mitochondrial DNA or mtDNA
for short.
It's much smaller than the DNA that makes up
our twenty three pairs of chromosomes,
but since
it contains the same kind of markers,
the little genetic typos that pass
unshuffled from generation to generation
on the maternal line.
So by looking at markers on the Y
chromosome and mitochondrial DNA
we can connect people alive today to
ancestors have lived tens of thousands
of years ago.
Over the last several years the
Genographic Project has studied the Y
chromosomes and the mitochondrial DNA
of more than half a million people and
we now know that everyone on earth
belongs to one of hundreds of distinct
groups of related people based on which
markers they have on their Y chromosome
Or mitochondrial DNA.
We call these groups haplogroups.
Each person in these groups traces their
descent from a common ancestor.
Haplogroups - your branch on the human
family tree.
